研究者詳細 - 小山　佳一

Mitsui Y., Watanabe Y., Kobayashi R., Takahashi K., Koyama K. . Effects of Magnetic Field Intensity on the Reaction in Mn/Ga Diffusion Couple . Journal of Electronic Materials54 ( 7 ) 5130 - 5136 2025年7月

記述言語：日本語出版者・発行元：Journal of Electronic Materials

The applied magnetic field intensity and the magnetic state of the reacted phase are important factors for in-magnetic-field phase growth. In this study, the in-magnetic-field reaction in Mn/Ga diffusion couples was analyzed under applied magnetic fields of up to 15 T at 573 K and 773 K. It was found that the growth rates of the Ga-rich phases (λMnGa and Mn<inf>2</inf>Ga<inf>5</inf> phases) showed different behavior with respect to the magnetic field intensity when the Mn-rich phases (Mn<inf>3</inf>Ga and γMnGa phases) were ferromagnetic at 573 K and paramagnetic at 773 K. At 573 K, the thicknesses of the Ga-rich phases at 5 T became thinner than the same phases at 0 T, and further decreased asymptotically under a higher magnetic field of 15 T. The thicknesses of the Mn-rich phases were independent of the magnetic field intensity. At 773 K, the thicknesses of the Ga-rich phases in a 10 T-annealed sample were reduced to 45–55% of the corresponding thicknesses in a 5 T-annealed sample. These behaviors were explained based on the contribution of the Zeeman energy to the formation enthalpy of the Mn-Ga phases in the ferromagnetic and paramagnetic regions.

DOI： 10.1007/s11664-025-11898-4

Mitsui Y., Fumoto S., Kobayashi R., Takahashi K., Koyama K. . High Magnetic Field Effects on Phase Transformation Kinetics of ε-Mn-Al Probed Using Differential Thermal Analysis . MATERIALS TRANSACTIONS66 ( 2 ) 230 - 235 2025年2月査読

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

Differential thermal analysis (DTA) on quenched Mn55Al45 with hcp structure (ε-phase) was performed under magnetic fields up to 15 T in order to investigate the magnetic field effects on the transformation kinetics of ε-phase. So far, the annealing of ε-phase under magnetic field indicated the acceleration of the phase transformation from the ε-phase to the metastable ferromagnetic τ-phase with L10 structure and the suppression of the decomposition into the equilibrium phase (β-phase). In this study, as the magnetic field intensity increased, the transformation temperature from ε-phase gradually decreased to the lowest value in the range from 0 to 4 T. A single exothermic peak was observed on each DTA curve, and it was found that the peak contained plural exothermic ε–τ and τ–β transformations. Activation energy of the transformation also showed the lowest value in the magnetic field range from 4 to 10 T, suggesting that the activation energy of the ε–τ transformation decreases at low magnetic field region from 0 to 4 T and the activation energy of the τ–β transformation increases at high magnetic field region from 10 to 15 T. These changes in activation energy were discussed by contribution of Zeeman energy for nucleation of the τ-phase in the ε-matrix and that of β-phase from the τ-phase. [doi:10.2320/matertrans.MT-M2024129]

DOI： 10.2320/matertrans.mt-m2024129

Sueyoshi Y., Kobayashi R., Onoue M., Mitsui Y., Umetsu R.Y., Koyama K. . Structural and Magnetic Properties of MnCo1-xFexGe1-ySiy (x, y = 0, 0.5) . MATERIALS TRANSACTIONSadvpub ( 0 ) 758 - 763 2025年査読

記述言語：英語出版者・発行元：公益社団法人日本金属学会

Magnetic and structural properties of MnCo<inf>1−x</inf>FexGe<inf>1−y</inf>Siy (x, y = 0, 0.5) were investigated using X-ray powder diffraction and magnetization measurements in the temperature (T) range from 5 to 370 K and in magnetic fields up to μ<inf>0</inf>H = 5 T. At room temperature, MnCoGe and MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> were the orthorhombic crystal structure (M-phase), MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge was the hexagonal crystal structure (P-phase), and MnCo0.5Fe0.5Ge0.5Si0.5 had two-phase coexistence of the M- and P-phases. MnCoGe and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge were a simple ferromagnetic and their Curie temperatures (TC) were determined to be 340 K and 200 K, respectively. MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge<inf>0.5</inf>Si<inf>0.5</inf> in μ0H ≤ 1 T showed a gentle dip in thermomagnetic curves at 10 ≤ T ≤ 100 K below TC which disappears when a magnetic field of μ0H > 3 T was applied. The magnetization curves of MnCoGe<inf>0.5</inf>Si<inf>0.5</inf> and MnCo<inf>0.5</inf>Fe<inf>0.5</inf>Ge<inf>0.5</inf>Si<inf>0.5</inf> at 5 K exhibited that a metamagnetic transition with the magnetic hysteresis in 0 < μ<inf>0</inf>H < 3 T. Our results suggest that substituting Fe for Co in MnCoGe system weakens the ferromagnetic interaction, whereas substituting Si for Ge strengthens the antiferromagnetic interaction.

DOI： 10.2320/matertrans.mt-mbw2024001

Kobayashi R., Fumoto S., Mitsui Y., Takahashi K., Koyama K. . Differential Thermal Analysis of Ferromagnetic Mn55Al45C2 and Mn53Zn2Al45 Under High Magnetic Fields . Journal of Electronic Materials 2025年

記述言語：日本語出版者・発行元：Journal of Electronic Materials

Magnetic field effects on the activation energy, E<inf>a</inf>, of phase transformation in the hcp phase of Mn<inf>55</inf>Al<inf>45</inf>C<inf>2</inf> and Mn<inf>53</inf>Zn<inf>2</inf>Al<inf>45</inf> were investigated by differential thermal analysis (DTA) under high magnetic fields up to 10 T. Single exothermic peak including plural transformations was observed for both Mn<inf>55</inf>Al<inf>45</inf>C<inf>2</inf> and Mn<inf>53</inf>Zn<inf>2</inf>Al<inf>45</inf>. No systematic magnetic field dependence of transformation temperature was observed for either Mn<inf>55</inf>Al<inf>45</inf>C<inf>2</inf> or Mn<inf>53</inf>Zn<inf>2</inf>Al<inf>45</inf>. E<inf>a</inf> for Mn<inf>55</inf>Al<inf>45</inf>C<inf>2</inf> and Mn<inf>53</inf>Zn<inf>2</inf>Al<inf>45</inf> under magnetic fields showing different behavior. E<inf>a</inf> for Mn<inf>55</inf>Al<inf>45</inf>C<inf>2</inf> monotonically increased with increasing magnetic field intensity, whereas E<inf>a</inf> for Mn<inf>53</inf>Zn<inf>2</inf>Al<inf>45</inf> had a minimum value at 5 T. These magnetic field effects on E<inf>a</inf> have been discussed by dividing the reduction effect of E<inf>a</inf> (transformation to ferromagnetic phase) in the lower magnetic field region and the enhancement effect of E<inf>a</inf> (transformation from ferromagnetic phase) in the higher magnetic field region.

DOI： 10.1007/s11664-025-12057-5

Onoue M., Mitsui Y., Kobayashi R., Umetsu R.Y., Uwatoko Y., Koyama K. . Magnetic field effect on decomposition of Sm2Fe17N3 probed using 57Fe Mössbauer spectroscopy . Interactions245 ( 1 ) 2024年12月

記述言語：日本語出版者・発行元：Interactions

In order to clarify the influence of the magnetic field on the thermal decomposition of Sm<inf>2</inf>Fe<inf>17</inf>N<inf>3</inf> powder, we conducted a heat-treatment (HT) experiment in a vacuum of 38 Pa, at a temperature of 723 K, and in a magnetic field of zero and 5 T. Results of X-ray diffraction measurement, temperature dependence of magnetization and 57Fe Mössbauer spectroscopy experiments showed that fully-nitride Sm<inf>2</inf>Fe<inf>17</inf>N<inf>3</inf> decomposes to nitrogen-poor Sm<inf>2</inf>Fe<inf>17</inf>N<inf>x</inf> (0 < x < 3), α-Fe, Fe<inf>2</inf>O<inf>3</inf> and Fe<inf>3</inf>O<inf>4</inf>. The magnetic field promoted the thermal decomposition of Sm<inf>2</inf>Fe<inf>17</inf>N<inf>3</inf> in this HT condition.

DOI： 10.1007/s10751-024-01942-w

Koyama K., Mitsui Y., Imatsuji S., Onaka A., Kobayashi R., Onoue M., Onodera R. . Study of heat treatment effect on magnetic properties of MnFeGe using 57Fe Mössbauer spectroscopy . Interactions245 ( 1 ) 2024年12月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Interactions

X-ray powder diffraction, magnetization, and 57Fe Mössbauer spectroscopy measurements were performed to investigate the effects of heat treatment on the magnetic properties of MnFeGe with hexagonal Ni2In-type structure. The samples were annealed at 1173 K for 24 h, as a solution treatment (ST), and then aged at 1073 K (AG-1073 K), 973 K (AG-973 K) and 773 K (AG-773 K). Curie temperature was the highest at AG-1073 K (201 K), and the lowest at AG-773 K (169 K). In ST and AG-1073 K, Mössbauer spectrum was represented by three subspectra. In AG-1073 K, 19% of the Fe atoms occupied 2a-site and 71% of the Fe atoms occupied 2d-site. The hyperfine fields of 2a- and 2d-sites at 15 K were 20.3 T and 9.99 T, respectively. Approximately 10% of the iron atoms contributed to the subspectrum of nonmagnetic phase. On the other hand, to represent the spectra obtained at 15 K for samples annealed at lower temperatures (AG-973 K and AG-773 K), an additional subspectrum with the hyperfine field of 21.6–22.0 T was required, which was due to the ferromagnetic impurity phase. The obtained results showed that as the aging temperature decreased, Fe occupying the 2a-site with a large hyperfine field decreased, resulting in a decrease in the macroscopic magnetic properties of MnFeGe.

DOI： 10.1007/s10751-024-01951-9

Mitsui Y., Baba K., Kobayashi R., Onoue M., Ito W., Kuzuhara S., Koyama K. . High magnetic field effects on the phase separation behaviour of Fe-15mass%Cu alloys probed by 57Fe Mössbauer spectroscopy . Interactions245 ( 1 ) 2024年12月

記述言語：日本語出版者・発行元：Interactions

High magnetic field effects on the phase separation of Fe-rich and Cu-rich phases in Fe-15mass%Cu were investigated using microstructural observation and 57Fe Mössbauer spectroscopy. Fe-15mass%Cu annealing was carried out at 773 K with or without a 5 T magnetic field. Microstructural observations showed that the Fe-rich grains were separated by a Cu-rich phase, and the width of the Cu-rich phase for the samples annealed at 5 T tended to be narrower than that of the samples annealed at 0 T. The Mössbauer spectrum of the samples measured at room temperature is represented by two sub-spectra. The hyperfine fields B<inf>hf</inf> of the two sub-spectra were 33.0–33.1 T and 31.4–31.7 T and they did not change with annealing time or the presence of a magnetic field. The spectrum with a higher (lower) B<inf>hf</inf> corresponded to the centre (near the grain boundary) of the Fe-rich grain. The occupancy of the spectrum with a lower B<inf>hf</inf> for the sample annealed at 5 T was larger than that for the sample annealed at 0 T by up to 5%. This indicated that the change of Cu concentration at the grain boundary became gentle. Therefore, the high magnetic field effects were coarsening of the Fe-rich grains and a gentle change in the Cu concentration at the grain boundary.

DOI： 10.1007/s10751-024-01939-5

Kobayashi R., Mitsui Y., Yoshizaki Y., Takahashi K., Takamine K., Koyama K. . Controlling the growth of yeast by culturing in high magnetic fields . Journal of Magnetism and Magnetic Materials586 2023年11月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

The effect of static magnetic fields up to a strength of 15 T on the growth of three types of yeast which were all classified as Saccharomyces cerevisiae was studied. The growth rate of the yeasts was suppressed by applying a magnetic field. The degree of suppression depended on the type of yeast. The reduction in the numbers of yeast cells was due to growth suppression, not sterilization. Among the three types of Saccharomyces cerevisiae, the degree of suppression on the growth of two yeasts was strongest in a magnetic field at 8 T with different suppression degree of 19% and 12% for a culture time of 24 h. Growth of the other yeast most suppressed by 10% at a magnetic field of around 4 T. Therefore, the yeasts have their characteristic magnetic field sensitivity on the growth. The results were discussed using a model based on the competition between yeast osmotic pressure changes by magnetic field and magnetic forces induced by magnetic field gradient. In low magnetic field regions, change of the osmotic pressure shrink the yeast cell and reduce the contact frequency between yeast cells and glucose-based ions. In higher magnetic field regions, effect of magnetic force become apparent, and recover the growth rate of the yeast. It suggested that the selective growth of yeast can be expected by in-magnetic-field culturing.

DOI： 10.1016/j.jmmm.2023.171193

Takaoka T., Mitsui Y., Koyama K., Fujii S. . Site Selectivity and Structural Stabilization in Cu-Doped or Fe-Doped MnCoGe . MATERIALS TRANSACTIONS64 ( 9 ) 2109 - 2112 2023年9月査読

記述言語：英語出版者・発行元：公益社団法人日本金属学会

We performed first-principles calculations to investigate the effect of Cu or Fe partial substitution in MnCoGe on the stabilization of the hexagonal structure. In the case of Cu partial substitution at x = 0.125, a substitution for one site is more effective than that for both sites. In the case of Fe partial substitution at x = 0.125, there is no difference between two types of substitution for both sites and the Mn site. The result of Fe partial substitution at x = 0.25 indicates that Fe partial substitution for both sites is more effective than that for the Mn or the Co site.

DOI： 10.2320/matertrans.mt-mg2022011

Nakamoto K., Mitsui Y., Kobayashi R., Koyama K. . In-Magnetic-Field Heat Treatment Effects on Phase Growth of Mn–Bi–Sn Composite . MATERIALS TRANSACTIONS64 ( 9 ) 2113 - 2117 2023年9月査読

記述言語：英語出版者・発行元：公益社団法人日本金属学会

To investigate the magnetic field effect on the synthesis reaction and phase growth in a Mn–Bi–Sn composite pellet, in-field heat treatments were performed in 5 T at 573 K for 1 to 48 hours. X-ray diffraction measurements and electron probe micro analysis revealed that MnBi phase did not appear but Mn3Sn, Mn3Sn2 and MnSn2 phases were detected in the pellet. In zero-field heat treatment, the phase fraction of Mn3Sn2 increased and that of MnSn2 decreased as the heat treatment time increased. In contrast, no significant change in the phase fractions of Mn3Sn2 and MnSn2 phase was observed in 5 T even if the heat treatment time was increased to 48 h. The obtained results suggested that the application of magnetic field suppressed the diffusion of Mn atoms between Mn–Sn phases.

DOI： 10.2320/matertrans.mt-mg2022014

Masahira ONOUE, Yoshifuru MITSUI, Saki IMATSUJI, Ryota KOBAYASHI, Reisho ONODERA, Keiichi KOYAMA . Magnetic Properties of MnFeGe Probed Using 57Fe Mössbauer-spectroscopy . JPS Conference Proceedings38 - 011139 2023年5月査読

Yoshifuru MITSUI, Hideto TANAKA, Masahira ONOUE, Moriharu NAGANO, Ryota KOBAYASHI, Rie Y. UMETSU, Keiichi KOYAMA . Magnetic and Hyperfine Properties of FeZnSb . JPS Conference Proceedings38 011138 2023年5月査読

Onaka A., Onoue M., Onodera R., Mitsui Y., Koyama K. . Magnetic and structural properties of Fe-substituted MnCoGe with Ni<inf>2</inf>In-type structure . Journal of Magnetism and Magnetic Materials563 170000 - 170000 2022年12月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

Site occupation of Fe atoms, magnetic and structural properties in MnCo1-xFexGe (x = 0.2, 0.5, 0.7 and 1.0) were investigated. Two phase co-existence of the hexagonal Ni2In-type structure (P-phase) and the orthorhombic TiNiSi-type structure was observed at room temperature for x = 0.2. For x = 0.5, 0.7 and 1.0, MnCo1-xFexGe was confirmed to be the P-phase. With increasing x from 0.2 to 1.0 for the P-phase, the lattice parameter ap slightly increased by only 0.14%, but cp decreased by 2.1%. As a result, when x was increased from 0.2 to 1.0, the unit cell volume of the P-phase decreased monotonously by 1.8%. The saturation magnetic moment and Curie temperature of MnCo0.5Fe0.5Ge were 2.16 μB/f.u. and 205 K, respectively, which decreased monotonically with increasing x. 57Fe Mössbauer spectroscopy indicated that 90–94% of the substituted Fe atoms occupied the Co-site but 10–6% of the Fe also occupied the Mn-site in the P-phase. For x = 0.5, 0.7 and 1.0, the hyperfine field at the Co-site was 8.29–9.44 T, which was larger than that at the Mn-site. The sign of quadruple splitting at the Co-sites changed from positive to negative with the increase of x, suggesting that the electric field gradients at Co-sites changed.

DOI： 10.1016/j.jmmm.2022.170000

Takahashi J., Mitsui Y., Onoue M., Kobayashi R., Koyama K. . Nitridation kinetics of Sm<inf>2</inf>Fe<inf>17</inf> probed using Mössbauer spectroscopy . Journal of Magnetism and Magnetic Materials554 2022年7月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

In this study, the Sm2Fe17 powder was subjected to nitridation at 743 K under N2 pressures of 0.05 and 0.1 MPa to investigate the growth kinetics of Sm–Fe–N. Two-phase growth of the fully nitride (FN) Sm2Fe17N3 phase and the nitrogen-poor (NP) Sm2Fe17Nx phase (0 < x < 3; x denotes the nitrogen content) was observed using 57Fe Mössbauer spectroscopy. Although the x value was greater at 0.05 MPa than at 0.1 MPa in the early stage of nitridation, the opposite trend was observed in the later stage. At a nitrogenation time of 24 h, nitridation was nearly complete at 0.1 MPa, while x tended to saturate and did not reach 3 at 0.05 MPa. The nitridation process was discussed based on two simultaneous growth processes: (i) the diffusion of the nitrogen atom in the NP phase and (ii) the nucleation and growth of the FN phase. A process combining N2 pressure and nitrogenation, which facilitated nitrogenation under low N2 pressure and high N2 pressure at the beginning and end of the nitridation process, respectively, achieved faster nitridation than process with a single N2 pressure.

DOI： 10.1016/j.jmmm.2022.169295

Fujii S., Mitsui Y., Koyama K. . Ab initio Study of Atomic-disorder Effect on Electronic and Magnetic Properties of CrAGe . Journal of the Physical Society of Japan91 ( 6 ) 2022年6月査読

記述言語：英語出版者・発行元：Journal of the Physical Society of Japan

First-principles calculations show that the atomic disorder between Al and Ge does not destroy the half-metallic character of CrAlGe, and that its unique character is, however, destroyed by the swap between Cr and Al (or Ge). Our analysis of the X-ray diffraction patterns of CrAlGe indicates the existence of this swap disorder.

DOI： 10.7566/JPSJ.91.064706

Kobayashi R., Mitsui Y., Umetsu R.Y., Takahashi K., Koyama K. . Acceleration of B2/L2<inf>1</inf> order-disorder transformation in Ni<inf>2</inf>MnAl Heusler alloys by in-magnetic-field annealing . Journal of Magnetism and Magnetic Materials547 2022年4月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

Ferromagnetic L21 phase of Ni2MnAl with high order degree is difficult to synthesize because of low L21/B2 order-disorder transformation temperature. It is found that magnetic field accelerated the transformation from the antiferromagnetic disordered B2 to ordered L21 phase. Magnetization increased by in-magnetic-field annealing at 673 K, which indicated the acceleration of the ordering to L21 phase. Magnetic field effects on the B2/L21 order-disorder transformation were discussed based on magnetic-field-induced change of transformation temperature, enhancement of degree of order at annealing temperature, and reduction of critical radius of L21 nuclei. Growth kinetics of L21 phase were evaluated by Johnson-Mehl-Avrami equation, which indicated that 15-T annealing accelerated the growth of L21 phase 5.7 times faster than zero-field annealing. Our results showed that magnetic field can contribute to shortening the annealing time for synthesis of ferromagnetic L21-Ni2MnAl alloy.

DOI： 10.1016/j.jmmm.2021.168908

Mitsui Y., Onoue M., Kobayashi R., Sato K., Kuzuhara S., Ito W., Takahashi K., Koyama K. . High Magnetic Field Effects on Cu-precipitation Behavior of Fe-1mass%Cu at 773 K . ＩＳＩＪ　Ｉｎｔｅｒｎａｔｉｏｎａｌ62 ( 3 ) 413 - 417 2022年3月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本鉄鋼協会

Tramp elements in steel, such as Cu and Sn, cannot be removed by acid treatment. Since these elements condense by repeating recycling process, leading to deterioration of strength. Therefore, the methods for avoiding condensation or removing tramp elements are required. In this study, in-magnetic-field annealing process was focused on because magnetic field is effective for diffusion, phase transformation, phase diagram and precipitation. In-magnetic-field annealing of Fe-1mass%Cu at 773 K was performed in 5 and 10 T for investigating precipitation behavior of supersaturated Cu. From microstructural observation, precipitation of Cu-rich phase in Fe-matrix, and magnetic field effect on itself were not observed clearly. Increase of the hyperfine field was detected for the samples annealed at 5 T by Mössbauer spectroscopy, indicating the enhancement of the Cu-precipitation. On the contrary, hyperfine field for 10T-annealed sample was slightly smaller than that for 0 T. Therefore, in-field annealing effect on Cu-precipitation became unclear at 10 T. These magnetic field effects were discussed in the viewpoints of the change of Cu–Fe phase diagram and the atomic diffusion under magnetic field. Difference of the magnetic field effects on precipitation between 5 T and 10 T is explained by the competition between the enhancement of the driving force of the precipitation and suppression of the atomic diffusion. The obtained results indicated that there is optimized magnetic field intensity for controlling Cu-precipitation.

DOI： 10.2355/isijinternational.isijint-2021-404

Hiroi M. . High magnetic field properties in Ru2-xFexCrSi with antiferromagnetic and spin-glass states . Physical Review B103 ( 9 ) 2021年3月査読

Kobayashi Ryota, Mitsui Yoshifuru, Umetsu Rie Y., Mizuguchi Masaki, Koyama Keiichi . Synthesis of Ferromagnetic τ-Mn–Al–C by Reactive Sintering . MATERIALS TRANSACTIONS62 ( 1 ) 130 - 134 2021年査読

記述言語：英語出版者・発行元：公益社団法人日本金属学会

Ferromagnetic Mn–Al–C (τ-phase) can be synthesized by a single-route conventional reactive sintering method. The maximum magnetization and coercivity were 75.8 Am2/kg and 57 mT, respectively. The τ-phase fraction was evaluated to be 81 mass% for Mn55Al45C2 annealed at 1273 K. The τ-phase of Mn55Al45C2 can be synthesized at an annealing temperature from 873 to 1273 K, whereas that of Mn55Al45 cannot be synthesized. It was indicated that the phase stability of the hcp-phase (ε-phase) was improved by adding carbon, resulting in an ε–τ transformation.

DOI： 10.2320/matertrans.MT-M2020166

Kobayashi Ryota, Takaki Akio, Mitsui Yoshifuru, Umetsu Rie Y., Takahashi Kohki, Mizuguchi Masaki, Koyama Keiichi . Dual Acceleration of ε-τ Transformation in Mn–Al Induced by Zn-Addition and In-Magnetic-Field Annealing . MATERIALS TRANSACTIONS62 ( 1 ) 124 - 129 2021年査読

記述言語：英語出版者・発行元：公益社団法人日本金属学会

Combined accelerating effects of ε–τ phase transformation by in-magnetic-field annealing and Zn-addition were investigated for Mn53Zn2Al45 in magnetic fields up to 15 T. The in-field annealing for Zn-added sample accelerated the ε–τ transformation 16 times faster than Mn55Al45 at annealing temperature of 623 K. The reduction of magnetization after finishing ε–τ transformation was also more rapid than that of Mn55Al45. However, magnetic-field-induced acceleration of ε–τ phase transformation and suppression of precipitation of β-phase were observed for Zn-added alloy Mn53Zn2Al45 annealed at 573 K. The obtained results suggested that the β-phase stabilized against both τ- and ε-phases by Zn-addition. Therefore, although the ε–τ transformation was efficiently accelerated by in-field annealing of Mn53Zn2Al45, more precisely control of annealing time is required for obtaining high fraction of ferromagnetic τ-phase.

DOI： 10.2320/matertrans.MT-M2020235

Yumi Watanabe, Ryota Kobayashi, Yoshifuru Mitsui, Rie Y. Umetsu, Keiichi Koyama . Magnetic-field-induced selective retardation of reaction in Mn/Ga diffusion couple . Journal of Alloys and Compounds887 161310 - 161310 2021年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Alloys and Compounds

In-field heat treatments of a solid-liquid Mn/Ga diffusion couple were conducted at 573 and 673 K with and without a magnetic field of 5 T to investigate magnetic field effects on the phase formation. Formation of the β-Mn, Mn3Ga, γ-MnGa, λ-MnGa, Mn2Ga5, and MnGa4 phases was observed. The obtained results indicated that the reaction and phase growth of λ-MnGa and Mn2Ga5 proceeded by diffusion-controlled process for both heat treatments at 0 and 5 T. We confirmed that a magnetic field suppressed the phase growth of λ-MnGa and Mn2Ga5. The parabolic coefficients of the λ-MnGa and Mn2Ga5 phases were exponentially suppressed by applying magnetic field of 5 T. It is suggested that gain of Zeeman energy of Mn-rich phase played a key role for the magnetic-field-induced suppression of the formation of the λ-MnGa and Mn2Ga5 phases.

DOI： 10.1016/j.jallcom.2021.161310

Shun Nakagawa, Yoshifuru Mitsui, Ryota Kobayashi, Rie Y. Umetsu, Kohki Takahashi, Keiichi Koyama . Magnetic-field-induced decomposition in Cu2MnAl Heusler alloys . Journal of Magnetism and Magnetic Materials540 168411 - 168411 2021年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

A magnetic field enhanced the decomposition of a Cu2MnAl Heusler alloy. An aging treatment at 573 K under 10 T promoted decomposition of a L21 phase and hard magnetic properties were exhibited. The crystallite size of the L21 phase decreased on annealing over 12 h and approached 22 nm at zero field. However, the crystallite size of the L21 phase of the 5 T-annealed sample was almost half that of the 0-T-annealed sample and decreased rapidly, indicating enhanced grain refinement by in-field annealing. Decomposition of the L21 phase was more pronounced in the 10-T-aged sample. The hysteresis loop for 10-T-aged sample had a large coercive force of 232 mT and a magnetization of 13 Am2/kg. These properties were markedly different from those of the 0-T-annealed sample. An increase of nucleation owing to a decrease of critical radius caused grain refinement associated with decomposition and magnetic hardening of Cu2MnAl.

DOI： 10.1016/j.jmmm.2021.168411

Y. Mitsui, Y. Takanaga, R. Kobayashi, K. Koyama . Effect of carbon addition on the phase stability of hcp-Mn-Al . Physics B595 412379 2020年10月査読

M Onoue, R Kobayashi, Y Mitsui, RY Umetsu, Y Uwatoko, K Koyama . Magnetic field-induced nitridation of Sm2Fe17 . J. Alloys Comp.835 155193 2020年9月査読

Noguchi K., Mitsui Y., Hiroi M., Umetsu R.Y., Gouchi J., Uwatoko Y., Koyama K. . Effects of Substituted Elements on Spin Reorientation in Mn[2-x]Fe[x]Sb[1-y]Sn[y] . MATERIALS TRANSACTIONS61 ( 8 ) 1492 - 1495 2020年8月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

The spin reorientation and Curie temperature of Mn21xFexSb11ySny (0 ¯ x, y ¯ 0.15) compound were investigated by magnetization measurements. Spin reorientation temperature increased from 255 K at x = 0 to 383 K at x = 0.15, whereas it almost unchanged by Sn substitution. Curie temperature decreased down to 518 K with both Fe and Sn substitution. Substitution of Fe stabilized the ferrimagnetic state with magnetic moment lying in c-plane. Substitution of Sn induced the antiferromagnetic phase at low temperature. It was found that the magnetic hysteresis derived from quasi first-order magnetic phase transition exhibited at x 2 0.10 or T 2 300 K.

DOI： 10.2320/matertrans.mt-mn2019016

Koyama K., Onoue M., Kobayashi R., Mitsui Y., Umetsu R.Y., Uwatoko Y. . Magnetic Field Effect on Nitrogenation of Sm₂Fe₁₇ . MATERIALS TRANSACTIONS61 ( 8 ) 1487 - 1491 2020年8月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

Nitrogenation of Sm2Fe17 powder was performed under a zero field and a magnetic field of 5 T at 623, 673 and 743 K to clarify the magnetic field effect on nitrogenation. Applying a magnetic field of 5 T induced nitrogenation compared with zero-field nitrogenation, and almost fully nitride Sm2Fe17N2.9 was obtained at 743 K. Mössbauer spectroscopy results suggested that a 5-T magnetic field promoted the phase transformation to the fully-nitride Sm2Fe17N3 phase. The magnetic field effect was discussed based on the magnetic energy gain and magnetic properties of host Sm2Fe17 and fully nitride Sm2Fe17N3

DOI： 10.2320/matertrans.mt-mn2019012

K Noguchi, Y Mitsui, M Hiroi, RY Umetsu, J Gouchi, Y Uwatoko, K Koyama . Effects of Substituted Elements on Spin Reorientation in Mn2-xFexSb1-ySny . Mater. Trans.61 ( 8 ) 1492 - 1495 2020年8月査読

K Nagano, Y Okubo, Y Mitsui, K Koyama, S Fujii . Ab-Initio Study on Structural and Magnetic Properties of Fe-Doped MnCoGe . Mater. Trans.61 ( 8 ) 1434 - 1437 2020年8月査読

三井好古，尾上昌平，小山佳一 . 磁場中反応を利用した選択的磁性材料合成 . まてりあ59 ( 8 ) 422 - 428 2020年8月査読

Deguchi T., Matsubayashi K., Uwatoko Y., Koyama T., Kohara T., Nakamura H., Mitsui Y., Koyama K. . Magnetic Measurements of Narrow-Gap Semiconductor FeSb₂ under High Pressure . MATERIALS TRANSACTIONS61 ( 8 ) 1476 - 1479 2020年7月招待査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

Pressure effects on magnetic susceptibility» and energy gap Eg0 of narrow-gap semiconductor FeSb2 were investigated for the temperature range of 50300 K and pressures up to 13 kbar. The estimated Eg0 for ambient pressure, Eg0(0), was 29 meV. By application of pressure,» was suppressed, and Eg0(P) was estimated to be 52 meV for 13 kbar. The fourth-order expansion coefficient £ of the free energy in magnetization was positive and enhanced by applying pressures.

DOI： 10.2320/matertrans.mt-mn2019015

Tanaka A., Yoshinaga S., Mitsui Y., Sasaki H., Kanomata T., Koyama K. . Magnetic Properties of Weak Itinerant Electron Ferromagnet Au₄V . MATERIALS TRANSACTIONS61 ( 8 ) 1473 - 1475 2020年7月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

The magnetization measurements were carried out for polycrystalline Au4V in magnetic fields up to 130 kOe. The spontaneous magnetic moment ps was determined to be 0.255 ®B/V at 4 K by high field magnetization. The magnetization process was analyzed on the basis of Takahashi’s spin fluctuation theory for weak itinerant electron ferromagnets. The characteristic parameters of the spin fluctuation were estimated to be TA = 1.3 © 103 K and T0 = 2.3 © 103 K using the data for 110130 kOe.

DOI： 10.2320/matertrans.mt-mn2019011

Y. Mitsui, T. Hagio, K. Takahashi, K. Koyama, . High magnetic field effects on the solid-liquid reaction of Fe-Ga system . ISIJ International60 ( 4 ) 807 - 811 2020年4月査読

Noguchi K., Kobayashi R., Mitsui Y., Umetsu R., Gouchi J., Uwatoko Y., Koyama K. . Heat treatment effect on the magnetic properties and martensitic transformations of MnCoGe . Journal of Magnetism and Magnetic Materials499 2020年4月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

X-ray powder diffraction, differential scanning calorimetry, and magnetization measurements were performed to investigate the effects of heat treatment on the magnetic and structural properties of as-cast and aging treated MnCoGe. The martensitic transformation temperature of the as-cast sample was 526 K for its first heating cycle, which decreased with repeating thermal cycles of 300–1273 K. MnCoGe prepared by aging treatment of 873 K for 7 days showed a first-order magnetic transition, which was accompanied by a martensitic transformation at 307 K. However, the transformation was not detected when the aging temperature was increased up to 973 K. The martensitic transformation temperature and volume of the parent phase was found to have a positive correlation.

DOI： 10.1016/j.jmmm.2019.166199

濵﨑貢、⼭⼝光⾂、陳麗、⼩原益⼰、三井好古、⼩⼭佳⼀ . 光の回折と干渉の現象を調べる教材の開発と実験 . 鹿児島大学紀要52 7 - 14 2019年12月

Watanabe Y., Hagio T., Kobayashi R., Mitsui Y., Koyama K. . Phase formation of a solid-liquid MnGA diffusion couple under a magnetic field . MATERIALS TRANSACTIONS60 ( 10 ) 2195 - 2198 2019年10月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

In-field heat treatments of an Mn-Ga diffusion couple were performed at 773 K for 12, 24 and 48 h to investigate the phase formation under magnetic fields. Formation of the MnGa3, Mn2Ga5, MnGa, Mn3Ga2 and ¢-Mn phases was confirmed for magnetic fields of 0 T and 5 T. For a diffusion-controlled process, there is a parabolic relationship between the thickness of the phase layers and annealing time for the MnGa and Mn2Ga5 phases. The parabolic coefficients of MnGa and Mn2Ga5 for a zero magnetic field were determined as 8.7 © 10-3 µm2s-1 and 4.6 © 10-1 µm2s-1 respectively. For a magnetic field of 5 T, the parabolic coefficients were evaluated as 11 © 10-3 µm2s-1 for the MnGa phase and 4.5 © 10-1 µm2s-1 for the Mn2Ga5 phase.

DOI： 10.2320/matertrans.mt-maw2019013

Onoue M., Kobayashi R., Mitsui Y., Umetsu R., Uwatoko Y., Koyama K. . In-Field Heat Treatment Effect on Nitridation of Sm₂Fe₁₇ . MATERIALS TRANSACTIONS60 ( 10 ) 2179 - 2182 2019年10月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

An in-field heat treatment furnace utilized for a magnet with a 50 mm room-temperature bore was made to study magnetic field effect on gas-solid reaction. Using this furnace, nitridation of Sm2Fe17 powder was performed under a 5-T magnetic field and a 0.1-MPa nitrogen gas pressure for the temperature range 623 to 743 K. Applying a magnetic field of 5 T promoted nitridation by approximately 0.6 nitrogen atoms per formula unit compared with zero-field nitridation, and almost fully nitride Sm2Fe17N2.9 was obtained at 743 K.

DOI： 10.2320/matertrans.mt-maw2019009

小林領太、三井好古、梅津理恵、高橋弘紀、水口将輝、小山佳一 . 磁場印加による強磁性 τ-Mn-Al への相変態の促進 . 日本金属学会誌83 ( 6 ) 181 - 185 2019年査読

S. Eto, Y. Fukuda, Y. Mitsui, M. Ito, K. Koyama and S. Fujii . Stable Structure, Magnetic and Electronic Properties of (Mn,Cr)AlGe . J. Phys. Soc. Jpn.88 064709 2019年査読

Y. Watanabe, T. Hagio, R. Kobayashi, Y. Mitsui, K. Koyama . Phase Formation of a Solid-Liquid MnGa Diffusion Couple under a Magnetic Field . Mater. Trans. 60 2195 - 2198 2019年査読

M. Onoue, R. Kobayashi, Y. Mitsui, R. Y. Umetsu, Y. Uwatoko, K. Koyama . In-Field Heat Treatment Effect on Nitridation of Sm2Fe17 . Mater. Trans. 60 2179 - 2182 2019年査読

R. Kobayashi, Y. Mitsui, K. Takahashi, S. Uda, K. Koyama . In-field annealing and quenching for ferromagnetic MnBi under 19 T . IEEE Trans. on Magn.55 1000204 2019年査読

Y. Mitsui, R. Kobayashi, Y. Takanaga, A. Takaki, R.Y Umetsu, K. Takahashi, M. Mizuguchi, K. Koyama . Different Magnetic Field Effects on the ϵ-τ Phase Transformation Between (Mn, Zn)-Al and Mn-Al-C . IEEE Trans. on Magn.55 2100704 2019年査読

H. Masumitsu, S. Yoshinaga, Y. Mitsui, R.Y. Umetsu, M. Hiroi, Y. Uwatoko, K. Koyama . Weak itinerant-electron ferromagnetism of CrAlGe modified by 3d transition metal . J. Magn. Magn. Mater.492 165677 2019年査読

濵﨑貢、⼭⼝光⾂、陳麗、⼩原益⼰、三井好古、⼩⼭佳⼀ . 身近な材料を用いた金属の比熱を測定する教材の開発 . 鹿児島大学理学部紀要51 9 - 13 2018年12月

濵﨑貢、⼭⼝光⾂、陳麗、⼩原益⼰、三井好古、⼩⼭佳⼀ . 音を可視化して音の速さと振動数・波長を測定する教材の開発 . 鹿児島大学理学部紀要51 1 - 8 2018年12月

Noguchi K., Masumitsu H., Mitsui Y., Umetsu R., Hiroi M., Uwatoko Y., Koyama K. . Magnetic properties of Mn<inf>1-x</inf>TM<inf>x</inf>AlGe (TM = V, Fe, Cu) with Cu<inf>2</inf>Sb-type structure . AIP Advances8 ( 10 ) 2018年10月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Advances

The magnetic properties of Mn1-xTMxAlGe (TM = V, Fe and Cu) were investigated for x ≤ 0.2. The spontaneous magnetization decreased with increasing x. A remarkable decrease in the Curie temperature TC was observed for TM = Fe. For ferromagnetic MnAlGe (x = 0) and TM = nonmagnetic Cu (x = 0.2), Curie-Weiss law was confirmed. The compounds with TM = V and Fe (x = 0.2) did not show Curie-Weiss law, and the data of reciprocal susceptibility vs. temperature bent, indicating change of the magnetism from ferromagnetism. Obtained results suggested that the magnetic moments of V and Fe were aligned antiparallel to those of Mn, resulting in the ferrimagnetism-like behavior.

DOI： 10.1063/1.5043069

K. Noguchi, H. Masumitsu, Y. Mitsui, R.Y. Umetsu, M. Hiroi, Y. Uwatoko, K. Koyama, . Magnetic properties of Mn1-xTMxAlGe (TM = V, Fe, Cu) with Cu2Sb-type structure . AIP Advances 8 101433 2018年10月査読

H. Masumitsu, S. Yoshinaga, Y. Mitsui, R.Y. Umetsu, M. Hiroi, Y. Uwatoko, K. Koyama . Cu-substitution effects on the magnetic properties of weak itinerant electron ferromagnet CrAlGe . AIP Advances 8 101426 2018年10月査読

Y. Okubo, S. Eto, Y. Mitsui, K. Koyama, S. Fujii . Ab initio investigation of Fe substitution effect on magnetostructural transition of CoMnGe . AIP Advances 8 101432 2018年8月査読

Masumitsu H., Yoshinaga S., Mitsui Y., Umetsu R., Hiroi M., Uwatoko Y., Koyama K. . Magnetic and structural properties of Mn<inf>1−</inf><inf>x</inf>Cr<inf>x</inf>AlGe (0 ≤ x ≤ 1.0) . Journal of Magnetism and Magnetic Materials456 104 - 107 2018年6月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

The magnetic and structural properties of Mn1−xCrxAlGe (0 ≤ x ≤ 1.0) compounds were investigated. The spontaneous magnetization Ms and Curie temperature TC of Mn1−xCrxAlGe has a cusp at x = 0.2. The maximum values of Ms and TC are 1.74 μB/f.u. and 601 K, respectively. It was found that the tetragonal Cu2Sb-type structure was stable for 0 ≤ x ≤ 0.75, whereas orthorhombic TiSi2-type structure was observed for x ≥ 0.8. The reciprocal susceptibility as a function of temperature suggested that the magnetic moment of Cr is antiferromagnetically coupled with that of Mn in Cu2Sb-type structure.

DOI： 10.1016/j.jmmm.2018.02.022

Hiroi M., Ishikuma S., Shigeta I., Koyama K., Kondo A., Kindo K., Manaka H., Terada N. . Magnetization and magnetic phase diagram of Heusler compounds Fe<inf>3-y</inf>(Mn<inf>1-x</inf>V <inf>x</inf> ) <inf>y</inf> Si (y = 1 and 1.5) . Journal of Physics: Conference Series969 ( 1 ) 2018年4月査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Journal of Physics: Conference Series

Fe2MnSi exhibits a ferromagnetic transition at TC and another transition to a phase with antiferromagnetic components at a low temperature of TA . By substituting V for Mn, so as to obtain Fe2Mn1-xV x Si, TA decreases with x and then vanishes around x ∼ 0.2. In this study, the magnetic transitions are investigated by magnetization measurements for Fe2Mn1-xV x Si (y = 1, 0 ≤ x ≤ 0.2) in high magnetic fields up to ∼70 T and for Fe1.5(Mn1-xV x )1.5Si (y = 1.5, 0 ≤ x ≤ 0.1) up to 5 T. For y = 1.5, with increasing x, TC increases and TA decreases as for y = 1, and the rate of the decrease in TA with x is slightly smaller than for y=1. In the low magnetic field region, TA for y = 1 does not significantly change due to the magnetic field but a distinct decrease is observed in high fields. The critical field at 0 K of this transition in Fe2MnSi is found to be larger than 70 T, and with increasing x, the critical field decreases corresponding to the decrease of TA at zero field.

DOI： 10.1088/1742-6596/969/1/012099

Yoshinaga S., Mitsui Y., Umetsu R., Uwatoko Y., Koyama K. . Pressure effect on magnetic properties of weak itinerant electron ferromagnet CrAlGe . Journal of the Physical Society of Japan87 ( 1 ) 2018年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

The Pressure effect on the magnetic properties of the weak itinerant electron ferromagnet CrAlGe was investigated at pressures up to 1.0 GPa. The spontaneous magnetic moment ps and Curie temperature TC decreased with increasing applied pressure P. The pressure derivatives of ps and TC were dps=dP = -3.98 × 10-5 μB=MPa and dTC=dP = -6.58 × 10-3K=MPa, respectively. These obtained results are discussed on the basis of Takahashi's spin fluctuation theory for weak itinerant electron ferromagnets. The characteristic parameters T0 and TA increased with pressure.

DOI： 10.7566/JPSJ.87.014701

Y. Mitsui, R.Y Umetsu, K. Takahashi, K. Koyama . Reactive sintering process of ferromagnetic MnBi under high magnetic fields . J. Magn. Magn. Mater.453 231 - 235 2018年査読

Y. Mitsui, Y. Matsumoto, Y. Uwatoko, M. Hiroi, K. Koyama . Magnetic relaxation dynamics in thermally arrested Cr-modified Mn2Sb . J. Magn. Magn. Mater.461 62 - 68 2018年査読

Y. Mitsui, K. Koyama, M. Ohtsuka, R.Y. Umetsu, R. Kainuma, K. Watanabe . High field X-ray diffraction study for Ni46.4Mn38.8In12.8Co2.0 metamagnetic shape memory film . Metals7 364 2018年査読

S. Yoshinaga, Y. Mitsui, R. Y. Umetsu, Y. Uwatoko, K. Koyama . Pressure effect on magnetic properties of weak itinerant electron ferromagnet GrAlGe . J. Phys. Soc. Jpn87 014701 2018年査読

M. Onoue, R. Kobayashi, Y. Mitsui, M.Hiroi, K. Takahashi, A. Kondo, K. Kindo, Y. Uwatoko, K. Koyama . Magnetic and Structural Properties of MnCoGe with Minimal Fe and Sn Substitution . Mater. Trans. 59 1645 - 1650 2018年査読

M. Hiroi, S. Ishikuma, I. Shigeta, K. Koyama, A. Kondo, K. K., H. Manaka, N. Terada . Magnetization and magnetic phase diagram of Heusler compounds Fe3−y(Mn1−xVx)ySi (y= 1 and 1.5) . J. Phys.: Conf. Ser.969 012099-1 - 012099-4 2018年査読

H. Masumitsu, S. Yoshinaga, Y. Mitsui, R.Y. Umetsu, M. Hiroi, Y. Uwatoko, K. Koyama . Magnetic and structural properties of Mn1-xCrxAlGe (0 ≤ x ≤ 1.0) . J. Magn. Magn. Mater. 456 104 - 107 2018年査読

A.N. Nwodo, R. Kobayashi, T. Wakamori, Y. Matsumoto, Y. Mitsui, R.Y. Umetsu, M. Hiroi, K. Takahashi, Y. Uwatoko, K. Koyama . Magnetic Phase Transition of Mn1.9Fe0.1Sb0.9Sn0.1 . IEEE Magn. Lett.9 1400204-1 - 1400204-4 2018年査読

R. Kobayashi, Y. Mitsui, K. Takahashi, S. Uda, K. Koyama . In-field annealing and quenching for ferromagnetic MnBi under 19 T . IEEE Trans. on Magn.55 1000204-1 - 1000204-4 2018年査読

Nwodo A., Kobayashi R., Wakamori T., Matsumoto Y., Mitsui Y., Hiroi M., Takahashi K., Umetsu R., Uwatoko Y., Koyama K. . Quasi-First Order Magnetic Transition in Mn₁.₉Fe₀.₁Sb₀.₉Sn₀.₁ . MATERIALS TRANSACTIONS59 ( 3 ) 348 - 352 2018年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

The magnetic and structural properties of ferrimagnetic (FRI) Mn1.9Fe0.1Sb0.9Sn0.1 with a Cu2Sb-type tetragonal structure were studied by magnetization and high field X-ray diffraction (XRD) measurements in 10 ≤ T ≤ 773 K and in magnetic fields μ0H up to 5 T. The lattice parameters a and c at 285 K were estimated to be 0.407 nm and 0.655 nm, respectively. The saturation magnetization at 10 K was determined to be 39.1 Am2/kg. It was observed that a first order magnetic transition (FOMT) with a thermal hysteresis occurred in the vicinity of 310 K under low magnetic fields. This FOMT disappeared easily by applying magnetic fields over 0.4 T.

DOI： 10.2320/matertrans.m2017291

小山佳一、山下美咲、小林領太、三井好古、高橋弘紀、宇田聡 . 15T級強磁場中小型急冷炉の開発 . 鹿児島大学理学部紀要50 1 - 5 2017年12月

小山佳一、島田大輔、安達義也、三井好古、廣井政彦、上床美也 . 高圧力下におけるMn2Sb1-xGex (x = 0.05, 0.8, 0.1)の磁気特性 . 鹿児島大学理学部紀要50 12 - 18 2017年12月

小山佳一、平敦志、三井好古、高橋弘紀 . 強磁場中固相焼結で合成したMnBiの特性評価 . 鹿児島大学理学部紀要50 6 - 11 2017年12月

Mitsui Y. . High field X-ray diffraction study for Ni<inf>46.4</inf>Mn<inf>38.8</inf>In<inf>12.8</inf>Co<inf>2.0</inf> metamagnetic shape memory film . Metals7 ( 9 ) 2017年9月査読

D. Miyazaki, Y. Mitsui, R. Y. Umetsu, K. Takahashi, S. Uda, K. Koyama . Enhancement of the Phase Formation Rate during In-Field Solid-Phase Reactive Sintering of Mn-Bi . Mater. Trans.58 720 - 728 2017年4月査読

R. Kobayashi, Y. Mitsui, R.Y. Umetsu, K. Takahashi, M. Mizuguchi, K. Koyama . Annealing temperature and magnetic field effects for ε−τ transformation in Mn-Al alloys . IEEE Magn. Lett.8 1400704 2017年1月査読

S. Yoshinaga, Y. Mitsui, R.Y. Umetsu, Y. Uwatoko, K. Koyama . Magnetic properties of weak itinerant electron ferromagnet CrAlGe . J. Phys. Conf. Ser.868 012018 2017年1月査読

S. Yoshinaga, S. Miura, T. Kanomata, Y. Mitsui, K. Koyama . Pressure Effect on Magnetism of Weak Itinerant Electron Ferromagnet Ni74.6Al25.4 . IEEE Magn. Lett.8 140043 2017年1月査読

T. Wakamori, Y. Mitsui, K. Takahashi, R.Y. Umetsu, Y. Uwatoko, M. Hiroi, K. Koyama . Thermal Transformation Arrest Phenomena in Mn2Sb0.9Sn0.1 . IEEE Magn. Lett.8 1402404 2017年1月査読

M. Hiroi, T. Tazoko, H. Sano, I. Shigeta, K. Koyama, A. Kondo, K. Kindo, H. Manaka, N. Terada . High-field magnetization of Heusler compound Fe2Mn1-xVxSi . Phys. Rev. B95 014410 2017年1月査読

M. Hiroi, H. Sano, T. Tazoko, I. Shigeta, M. Ito, K. Koyama, H. Manaka, N, Terada, M. Fujii, A. Kondo, K. Kindo . Magnetic and electrical properties of Heusler compounds Ru2Cr1-xXxSi (X = V, Ti) . J. Alloys. Comp.694 1376 - 1382 2017年1月査読

M. Yamashita, K. Abematsu, K. Takahashi, Y. Mitsui, K. Koyama . Development of a compact quenching furnace used under high magnetic fields . IEEE Magn. Lett.8 1400704 2017年1月査読

R. Kobayashi, Y. Mitsui, R.Y. Umetsu, K. Takahashi, M. Mizuguchi, K. Koyama . Magnetic-Field-Induced Acceleration of Phase Formation in τ-Mn-Al . Mater. Trans.58 1511 - 1518 2017年査読

Shigeta I. . Fabrication and characterization of epitaxial films of superconductor NbN and highly spin-polarized heusler alloy Co<inf>2</inf>2Fe<inf>0.4</inf>Mn<inf>0.6</inf>Si . IEEE Magnetics Letters8 1 - 5 2017年査読

Kobayashi R. . Effects of Annealing Temperature and Magnetic Field on the ϵ-τ Phase Transformation in Mn-Al Alloys . IEEE Magnetics Letters8 2017年査読

Yamashita M., Abematu K., Takahashi K., Mitsui Y., Koyama K. . Development of a Compact Quenching Furnace for Use in High Magnetic Fields . IEEE Magnetics Letters8 2017年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Magnetics Letters

A compact quenching furnace used under high magnetic fields was developed. The range of the annealing temperature and magnetic field of this apparatus was T ≤ 643 K and μ0H ≤ 15 T. The cooling rate was about 40 K/s in magnetic field of μ0H = 15 T. As a performance test of the furnace, an in-field heat treatment at 643 K and in-field quenching were carried out for a Mn-Bi ferromagnet. The magnetic field effect on the phase equilibrium between MnBi and Mn1.08Bi was examined.

DOI： 10.1109/LMAG.2016.2621733

Hiroi M., Sano H., Tazoko T., Shigeta I., Ito M., Koyama K., Manaka H., Terada N., Fujii M., Kondo A., Kindo K. . Magnetic and electrical properties of Heusler compounds Ru2Cr1−xXxSi (X = V, Ti) . Journal of Alloys and Compounds694 1376 - 1382 2017年

記述言語：日本語出版者・発行元：Journal of Alloys and Compounds

Two series of Heusler compounds Ru<inf>2</inf>Cr<inf>1−x</inf>X<inf>x</inf>Si (X = V, Ti) are synthesized, and their magnetic and electrical properties are investigated. Overall, these two series of compounds are identical in numerous properties. The measurements of magnetic properties reveal that an antiferromagnetic transition observed for x = 0 becomes smeared and it changes into a spin-glass state with increasing x. Around x = 0.5 this behavior disappears and it becomes paramagnetic. High-field magnetization for x = 0.3 and 0.4 up to 62 T exhibits no sign of magnetic transition or saturation of the magnetization. In the temperature dependence of resistivity, the kink that indicates the antiferromagnetic transition observed for x = 0 becomes invisible even for x ∼ 0.1. This also exemplifies that the antiferromagnetic order is destroyed by the substitution and is replaced by the spin-glass state. Concerning the resistivity, these samples exhibit semiconducting behavior for small x, whereas with increasing x ≳ 0.5 they turn to show metallic behavior and Ru<inf>2</inf>VSi becomes a paramagnetic metal. Nevertheless, Ru<inf>2</inf>TiSi shows a tendency for semiconductivity again.

DOI： 10.1016/j.jallcom.2016.09.276

X. F. Miao, Y. Mitsui, A. Iulian Dugulan, L. Caron, N. V. Thang, P. Manuel, K. Koyama, K. Takahashi, N. H. van Dijk, and E. Brück . Kinetic-arrest-induced phase coexistence and metastability in (Mn,Fe)2(P,Si) . Phys. Rev. B94 094426 2016年12月査読

M. Onoue, K. Ozono, Y. Mitsui, M. Hiroi, R.Y. Umetsu, Y. Uwatoko, K. Koyama . Magnetic properties of MnCo1-xFexGe (x = 0.08, 0.12) . 鹿児島大学理学部紀要49 11 - 15 2016年12月

A. Takaki, Y. Mitsui, D. Miyazaki, R.Y. Umetsu, K. Takahashi, K. Koyama . Magnetic field effects on the morphology of Bi-Mn alloy prepared by solid-phase reactive sintering . 鹿児島大学理学部紀要49 17 - 21 2016年12月

Y. Matsumoto, K. Matsubayashi, Y. Uwatoko, M. Hiroi, Y. Mitsui, K. Koyama . Magnetic Properties of Mn1.9Cu0.1Sb under High Pressure . AIP Conf. Proc.1763 0020005 2016年8月査読

K. Abematsu, Y. Mitsui, A. Taira, D. Miyazaki, A. Takaki, R.Y. Umetsu, K. Takahashi, K. Koyama . Magnetic Field Effects on Reactive Sintering of MnBi . AIP Conf. Proc. 1763 0020010 2016年8月査読

T. Wakamori, Y. Mitsui, K. Takahashi, R.Y. Umetsu, M. Hiroi, K. Koyama . High Field X-ray Diffraction Measurements of Mn2Sb0.95Ge0.05 . AIP Conf. Proc. 1763 0020006 2016年8月査読

K. Ozono, Y. Mitsui, R. Y. Umetsu, M. Hiroi, K. Takahashi, K. Koyama . Magnetic and Structural Properties of MnCo1-xFexGe (0 ≤ x ≤ 0.12) . API Conf. Proc.1763 002003 2016年8月査読

K. Ozono, Y. Mitsui, M. Hiroi, R.Y. Umetsu, K. Takahashi, K. Matsubayashi, Y. Uwatoko, K. Koyama . Magnetic and Structural Properties of Metamagnetic MnCo0.92Fe0.08Ge Compound . Mater. Trans.57 ( 3 ) 316 - 320 2016年3月査読

小野寺礼尚、大武和樹、高橋弘紀、木村尚次郎、渡辺和雄、小山佳一 . 高温・強磁場中磁化測定によるFeRh合金のメタ磁気相転移の観測 . 日本金属学会誌80 ( 3 ) 186 - 191 2016年3月査読

Y. Mitsui, K. Abematsu, R.Y. Umetsu, K. Takahashi, K. Koyama . Magnetic field effects on liquid-phase reactive sintering of MnBi . J. Magn. Magn. Mater.400 304 - 306 2016年1月査読

Ozono K., Mitsui Y., Umetsu R., Hiroi M., Takahashi K., Koyama K. . Magnetic and Structural Properties of MnCo<inf>1-x</inf>FexGe (0 ≤ x ≤ 0.12) . AIP Conference Proceedings1763 2016年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AIP Conference Proceedings

Structural, magnetic and thermal properties of ferromagnetic MnCo1-xFexGe (0 ≤ x ≤ 0.12) compounds were investigated. The Curie temperature TC and the martensitic transformation temperature TM of MnCoGe (x = 0) were determined to be 340 K and 510 K, respectively. With increasing x from 0 to 0.08, TM decreased and reached room temperature (290 K) for x ∼ 0.08. For x > 0.09, MnCo1-x Fex Ge did not exhibit the martensitic transformation. The compound for x ∼ 0.08 showed a first-order magnetic transition with a thermal hysteresis of 20 K and was accompanied by the martensitic transformation in the vicinity of room temperature. The phase diagram of MnCo1-x Fex Ge (0 ≤ x ≤ 0.12) is presented.

DOI： 10.1063/1.4961336

D. Miyazaki, Y. Mitsui, K. Abematsu, K. Takahashi, K. Watanabe, S. Uda, K. Koyama . In-situ observation and differential thermal analysis of MnBi in high magnetic fields . Physics Procedia75 1324 - 1331 2015年12月査読

S. Yoshinaga, Y. Mitsui, R.Y. Umetsu, K. Koyama . Magnetic properties of Cr-based ternary compound CrAlGe . Physics Procedia75 918 - 925 2015年12月査読

Y. Mitsui, Y. Yoshimine, R.Y. Umetsu, K. Matsubayashi, Y. Uwatoko, M. Hiroi, K. Koyama . Pressure Effect on the Martensitic Transformation and Magnetic Properties of Mn2−xNi1+xGa . 鹿児島大学理学部紀要48 35 - 39 2015年12月

K. Koyama, D. Shimada, Y. Adachi, H. Orihashi, D. Mitsunaga, M. Hiroi, Y. Mitsui, S. Kimura, K. Matsubayashi, Y. Uwatoko . Magnetic and electrical properties of Mn2Sb1−xZx (Z = Ge, Sn) under high pressures and high magnetic fields . Rep. Fac. Sri., Kagoshima Univ.48 15 - 21 2015年12月

R. Onodera, S. Kimura, K. Watanabe, Y. Yokoyama, A. Makino, K. Koyama . Nucleation control for fine nano crystallization of Fe-based amorphous alloy by high-magnetic-field annealing . J. Alloys Comp.637 213 - 218 2015年7月査読

Mitsui Y., Ikehara Y., Takahashi K., Kimura S., Miyamoto G., Furuhara T., Watanabe K., Koyama K. . Fe-Feinf3/infC binary phase diagram in high magnetic fields . Journal of Alloys and Compounds632 251 - 255 2015年5月

記述言語：日本語出版者・発行元：Journal of Alloys and Compounds

The Fe-Feinf3/infC binary phase diagram under high magnetic fields up to 21 T was investigated by a differential thermal analysis. Applying a magnetic field of 18 T, the α-γ transformation temperature Tinfα-γ/inf for pure iron increased quadratically from 1181 K (a zero field) to 1206 K. With increasing magnetic field strength, the transformation temperature Ainfc1/inf (α-Fe + cementite → α-Fe + γ-Fe) increased linearly from ∼1000 K to ∼1030 K at the rate of 1.4-1.5 K Tsup-1/sup. The transformation temperature Ainfc3/inf (α-Fe + γ-Fe → γ-Fe) for Fe-0.18 wt.%C and Fe-0.38 wt.%C increased quadratically by 27 K under a 18-T field. The Ainfc1/inf and Ainfc3/inf lines shifted to higher temperatures by the magnetic field, resulting in a change in the Fe-Feinf3/infC phase diagram. The results obtained suggest that the transformation temperatures mainly arose because of the Zeeman energy of α-Fe under high magnetic fields.

DOI： 10.1016/j.jallcom.2015.01.129

Y. Mitsui, Y. Ikehara, K. Takahashi, S. Kimura, G. Miyamato, F. Furuhara, K. Watanabe, K. Koyama . Fe-Fe3C binary phase diagram in high magnetic fields . J. Alloys Comp.632 251 - 255 2015年3月査読

Yoshifuru Mitsui, Yuki Yoshimine, Rie Y. Umetsu, Kazuyuki Matsubayashi, Yoshiya Uwatoko, Masahiko Hiroi, Keiichi Koyama . Pressure Effect on the Martensitic Transformation and Magnetic Properties of Mn2-xNi1+xGa . 鹿児島大学理学部紀要48 35 - 39 2015年

Goto J., Kakimoto T., Fujii S., Koyama K. . Site Preference and Stabilization of Antiferromagnetism in M-Substituted Mn₂₋xMxSb (M = Ti, Cr, Co, or Cu) . MATERIALS TRANSACTIONS56 ( 3 ) 415 - 423 2015年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

We applied first-principles total-energy calculations to several compounds Mn2-xMxSb (M = Ti, Cr, Co, or Cu) to calculate the total energy. The results indicate that the Ti and Cu (Cr and Co) atoms prefer the Mn(II) site to the Mn(I) site [Mn(I) to Mn(II)]. These results are consistent with experimental observations. The antiferromagnetism (AF) [ferrimagnetism (FR)] is more stable than FR (AF) upon decreasing (increasing) the distance between the Mn(II) and Sb atoms in the z direction in all Mn2-xMxSb systems. This result indicates that the environment around the Mn atom plays a very important role in the stabilization of the AF state, as is the case with Mn2Sb1-xAsx systems. For Mn2-xCoxSb systems, the atomic disorder between the Mn and Co atoms is insensitive to the relative stability of two magnetic phases AF and FR.

DOI： 10.2320/matertrans.m2014417

Y. Mitsui, R.Y. Umetsu, K. Koyama and K. Watanabe . Magnetic-field-induced enhancement for synthesizing ferromagnetic MnBi phase by solid-state reaction sintering . J. Alloys Comp.615 131 - 134 2014年12月査読

小山佳一, 五十嵐利行, 渡辺和雄 . HfV2の強磁場と高圧下における磁気的,熱伝的及び構造的特性 . 鹿児島大学理学部紀要47 13 - 19 2014年12月

T. Kakimoto, J. Goto, S. Fujii, K. Koyama and S. Ishida . Electronic and magnetic properties of Mn2Sb1-xAsx (x = 0, 0.5, 1) . Mater. Trans. 55 ( 12 ) 1878 - 1884 2014年12月査読

T.M. Pan,C.H. Chen, J.L. Her, K. Koyama . Comparison of structural and electrical properties of Lu2O3 and Lu2TiO5 gate dielectrics for alpha-InGaZnO thin-film transistors . J. Appl. Phys.116 ( 19 ) 194510 - -4 2014年11月査読

J.L. Her, T.M. Pan, J.H. Liu, H.J. Wang, C.H. Chen, K. Koyama . Electrical characteristics of GdTiO3 gate dielectric for amorphous InGaZnO thin-film transistors . Thin Solid Films569 6 - 9 2014年10月査読

Y. Mitsui, K. Koyama, K. Oikawa, K. Watanabe . Magnetic field effect on the liquid boundary of Bi-Mn binary system . AIP Conference Proceedings1618 269 - 272 2014年10月

T.M. Pan, F.H. Chen, M.N. Hung, J.L. Her, K. Koyama . Structural Properties and Electrical Characteristics of High-kappa Tm2O3 Gate Dielectrics for InGaZnO Thin Film Transistors . Sci. Adv. Mater. 6 ( 9 ) 1973 - 1978 2014年9月査読

Y. Mitsui, R.Y.Umetsu, K. Koyama, K. Watanabe . Magnetic-field-induced enhancement for synthesizing ferromagnetic MnBi phase by solid-state reaction sintering . J. Alloys. Comp.615 131 - 134 2014年6月査読

M. Yamamoto, K. Magishi, A. Hisada, T. Saito, K. Koyama, M. Takusari, H. Kato, C. Sekine . NMR Study of Filled Skutterudite Pr0.9Ce0.1Ru4P12 . JPS Conf. Proc.3 011003 (6 pages ) 2014年6月査読

三井好古, 池原佑基, 高橋弘紀, 渡辺和雄, 小山佳一 . 強磁場中示差熱分析によるFe-Cのα→γ変態に対する強磁場効果 . 熱測定41 ( 2 ) 43 - 48 2014年4月査読

R. Onodera, S. Kimura, K. Watanabe, Y. Yokoyama, A. Makino and K. Koyama . Crystallization kinetics of high iron concentration amorphous alloys under high magnetic fields . J. Alloys Comp.604 8 - 11 2014年4月査読

K. Abematsu, R.Y. Umetsu, R. Kainuma, T. Kanomata, K. Watanabe and K. Koyama . Structural and magnetic properties of magnetic shape memory alloy Ni46Mn41In13 under magnetic fields . Mater. Trans. 55 477 - 481 2014年4月査読

三井好古、小山佳一、淡路智、渡辺和雄 . 強磁場中熱分析 -相平衡への強磁場効果 . 低温工学49 ( 1 ) 11 - 18 2014年1月査読

T.M. Pan, H.C. Chen, J.H. Liu, F.H. Chen, J.L. Her, K. Koyama . Comparison of High-kappa Gd2O3 and GdTiO3 alpha-InGaZnO Thin-Film Transistors . IEEE TRANSACTIONS ON ELECTRON DEVICES61 ( 1 ) 87 - 91 2014年1月査読

S. Mondal, J.L Her,K. Koyama, T.M. Pan . Resistive switching behavior in Lu2O3 thin film for advanced flexible memory applications . NANOSCALE RESEARCH LETTERS9 3(8) 2014年1月査読

T.M. Pan, C.H. Chen, J.H. Liu, J.L. Her and. K. Koyama . Electrical and reliability characteristics of high-kappa HoTiO3 alpha-InGaZnO thin-film transistors . IEEE Trans. Device Lett35 66 - 68 2014年1月査読

Y. Yoshimine, D. Mitsunaga, H. Orihashi, D. Shimada, M. Hiroi, R. Onodera, S. Kimura, K. Takahashi and K. Koyama . Magnetic and electrical properties of Mn2-xNi1+xSb . IEEE Trans. Magn50 1001204 - -4 2014年1月査読

K. Ohtake, Y. Mitsui, K. Takahashi, R. Onodera,S. Kimura, K. Watanabe and K. Koyama . X-ray diffraction measurements of the Fe-Rh alloy under high magnetic fields and at high temperatures . IEEE Trans. Magn.50 1001404 - -4 2014年1月査読

Y. Matsumoto, H. Orihashi, K. Matsubayashi, Y. Uwatoko, M. Hiroi, K. Koyama . Magnetic field effect on magnetic and electrical properties of Mn2-xCuxSb . IEEE Trans. Magn.50 1000704 - -4 2014年1月査読

T. Tsutaoka, K. Obata, S. Cheyvuth and K. Koyama . Magnetic phase transitions in Er7Rh3 studied on single crystals . J. Alloy Comp.606 214 - 218 2014年査読

S. Mondal, J.L.Her, K. Koyama, and T.M Pan . Resistive switching behavior in Lu2O3 thin film for advanced flexible memory applications . Nanoscale Research Lett.9 3 2014年査読

Pan T., Chen F., Hung M., Her J., Koyama K. . Structural properties and electrical characteristics of high-κ Tm2O3 gate dielectrics for InGaZnO thin film transistors . Science of Advanced Materials6 ( 9 ) 1973 - 1978 2014年

記述言語：日本語出版者・発行元：Science of Advanced Materials

In this paper, we studied the structural properties and electrical characteristics of high-dielectric constant (high-κ) Tm<inf>2</inf>O<inf>3</inf> gate dielectrics for amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) applications. We used X-ray diffraction to determine the growth directions and crystallinity of the Tm<inf>2</inf>O<inf>3</inf> films, X-ray photoelectron spectroscopy to analyze the chemical structure of the films, and to monitor the morphological feature of the Tm<inf>2</inf>O<inf>3</inf> films after annealing at various temperatures. The high-κ Tm<inf>2</inf>O<inf>3</inf> a-IGZO TFT annealed at 400°C exhibited a lower threshold voltage of 1.68 V, a higher field effect mobility of 11.8 cm2/V-s, a larger I<inf>on</inf>/I<inf>off</inf> ratio of 3.9×107, and a smaller SS of 420 mV/dec., relative to those of the systems that had been subjected to other annealing conditions. This result suggests the Tm<inf>2</inf>O<inf>3</inf> film featuring a higher dielectric constant as well as a smoother surface. The V<inf>TH</inf> stability on high-κ Tm<inf>2</inf>O<inf>3</inf> IGZO TFTs was also explored under positive bias stress.

DOI： 10.1166/sam.2014.1963

Kakimoto T., Goto J., Fujii S., Koyama K., Ishida S. . Electronic and Magnetic Properties of Mn₂Sb₁₋xAs[x] (x = 0, 0.5, 1) . MATERIALS TRANSACTIONS55 ( 12 ) 1878 - 1884 2014年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

The electronic and magnetic properties of Mn2Sb1-xAsx (where x = 0, 0.5, 1) are investigated from first-principles total-energy calculations. The predicted magnetic ground states (ferrimagnetism for x = 0 and antiferromagnetism for x = 1) are in agreement with experimental observations; however, this is not the case for x = 0.5. Here, it is found that the artificial change of the surrounding atoms of Mn stabilizes the antiferromagnetism. A similar change stabilizes ferrimagnetism (antiferromagnetism) for x = 1 (x = 0). These results indicate that the environment around the Mn atoms plays a very important role in the stabilization of antiferromagnetism in the Mn2Sb1-xAsx system. In addition, an analysis of the sign of an effective exchange interaction as a function of the distance between the Mn atoms is performed.

DOI： 10.2320/matertrans.m2014251

Mitsui Y., Koyama K., Oikawa K., Watanabe K. . Magnetic field effect on the liquidus boundary of Bi-Mn binary system . AIP Conference Proceedings1618 269 - 272 2014年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AIP Conference Proceedings

The magnetic field effect (MFE) on liquidus boundary of Bi-Mn binary system was investigated by differential thermal analysis (DTA) and the computer coupling of phase diagram method (CALPHAD). The liquidus boundary for Bi-18at.%Mn and Bi-24at.%Mn rose clearly by the application of the magnetic fields. The MFE for liquidus boundary temperature Tliq changed from ΔTliq∞B2 to ΔTliq∞B because of the large increase of the peritectic temperature from BiMn and BiMn1.08 by the application of magnetic field.

DOI： 10.1063/1.4897725

Abematsu K., Umetsu R., Kainuma R., Kanomata T., Watanabe K., Koyama K. . Structural and magnetic properties of magnetic shape memory alloy Ni <inf>46</inf>Mn<inf>41</inf>In<inf>13</inf> under magnetic fields . MATERIALS TRANSACTIONS55 ( 3 ) 477 - 481 2014年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

The structural and magnetic properties of Heusler alloy Ni 46Mn41In13 were studied by magnetization and X-ray powder diffraction measurements in the 4.5350K temperature range and in magnetic fields up to 5 T. The alloy undergoes martensitic transformation from a L21-type cubic structure with ac = 0.600nm at 293K to a six-layered monoclinic (6M) structure in the transition temperature of 160230 K. The lattice parameters for the 6M structure were estimated to be am = 0.441 nm, bm = 0.557 nm, cm = 1.30 nm, αm = 90.0°, βm = 94.0°, and γm = 90.0° at 75 K. In this transformation from the L21 to 6M structures, the cell volume contracts by 0.34% at 8K. In addition, we observed the magnetic field-induced reverse transformation of this alloy. © 2014 The Japan Institute of Metals and Materials.

DOI： 10.2320/matertrans.m2013372

Chen C., Her J., Pan T., Chiu F., Koyama K. . Structural properties and electrical characteristics of high-k GdTiO<inf>3</inf> gate dielectrics for InGaZnO thin-film transistors . 2014 10th International Vacuum Electron Sources Conference, IVESC 2014 and 2nd International Conference on Emission Electronics, ICEE 2014 - Proceedings 2014年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：2014 10th International Vacuum Electron Sources Conference, IVESC 2014 and 2nd International Conference on Emission Electronics, ICEE 2014 - Proceedings

We investigated the structural properties and electrical characteristics of GdTiO3 dielectrics for IGZO TFT devices. We used XRD, XPS, and AFM to examine the structural, compositional, and morphological features of the GdTiO3 film, respectively. The IGZO TFT featuring a GdTiO3 gate dielectric exhibited a large field-effect mobility of 32.3 cm2/V-s, a small threshold voltage of 0.14 V, a high Ion/Ioff current ratio of 4.2 × 108, and a low subthreshold swing of 213 mV/decade.

DOI： 10.1109/IVESC.2014.6891962

M. Mitsui, R.Y. Umetsu, M. Saito, K. Koyama, H. Kawarada . Synthesis and diffusion of MnBi in high magnetic fields . The International Symposium on Ecotopia Science 2013 and The 5th International Symposium on Advanced Materials Development and Integration of Novel Structural Metallic and Inorganic Materials (ISETS’13 and AMDI-4) 1317 2013年12月

J. Goto, T. Kakimoto, S. Fujii and K. Koyama . Magnetic and electronic structures and Cobalt or Copper substituted Mn2Sb . Mater. Trans.54 ( 12 ) 2309 - 2312 2013年12月査読

後藤純哉、柿本貴俊、藤井伸平、小山佳一 . Electronic and magnetic structures of Cobalt substituted Mn2Sb . 日本金属学会誌77 ( 10 ) 461 - 465 2013年10月査読

Andreev A.V., Tereshina E.A., Gorbunov D.I., Šantavá E., Šebek J., Žáček M., Homma Y., Shiokawa Y., Satoh I., Yamamura T., Komatsubara T., Watanabe K., Koyama K. . Magnetic Anisotropy in Intermetallic Compounds Containing Both Uranium and 3d-Metal1 . Physics of Metals and Metallography114 ( 9 ) 727 - 733 2013年9月

記述言語：日本語出版者・発行元：Physics of Metals and Metallography

Magnetic properties of intermetallic compounds containing both uranium and a 3d metal (Fe, Co) are summarized and discussed. It was shown that the ordered magnetism of the U and 3d-metal sub- lattices can coexist in the same compound (e.g. with 2-17 and 1-12 stoichiometries) even at room and ele- vated temperatures. © Pleiades Publishing, Ltd., 2013.

DOI： 10.1134/S0031918X13090020

Y. Mitsui, K. Oikawa, K. Koyama and K. Watanabe . Thermodynamic assessment for the Bi-Mn binary phase diagram in high magnetic fields . J. Alloys Comp.577 315 - 319 2013年8月査読

Y. Mitsui, Y. Ikehara, K. Watanabe, E.S. Choi, E.C. Palm and K. Koyama . Thermal analysis on MnBi in high magnetic fields up to 45 T . J. Korean Phys. Soc.62 1769 - 1772 2013年8月査読

Shimada D., Orihashi H., Mitsunaga D., Ito M., Hiroi M., Koyama K., Onodera R., Takahashi K., Matsubayashi K., Uwatoko Y. . Magnetic properties of Mn<inf>2</inf>Sb<inf>1-x</inf>Ge<inf>x</inf> (0.05 ≤ x ≤ 0.2) in high magnetic fields . Journal of the Korean Physical Society63 ( 3 ) 747 - 750 2013年8月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Korean Physical Society

Magnetization and electrical resistivity measurements were carried out for polycrystalline Mn2Sb1-xGex (0.05 ≤ x ≤ 0.2) in magnetic fields up to 16 T in the 4.2 - 600 K temperature range in order to investigate the magnetic and the electrical properties under high magnetic fields. Mn2Sb0.92Ge0.08 showed a Curie temperature, T C, of 532 K and a first order magnetic transition from a ferrimagnetic (FRI) to an antiferromagnetic (AFM) phase at T t = 230 K with decreasing temperature in a zero magnetic field. With increasing x, T C decreased and T t increased. For Mn2Sb0.92Ge0.08, a matamagnetic transition from an AFM to a FRI phase was observed at 215 K. The magnetic phase diagram of Mn2Sb1-xGex is presented. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.747

R. Onodera, S. Kimura, K. Watanabe, Y. Yokoyama, A. Makino and K. Koyama . Isothermal Crystallization of Iron-Based Amorphous Alloys in a High Magnetic Field . Mater. Trans54 ( 7 ) 1232 - 1235 2013年7月査読

A.V. Andreev, E.A. Tereshina, D.I. Gorbunov, E. Santava, J. Sebek, M. Zacek, Y. Homma, Y. Shiokawa, I. Satoh, t. Yamamura, T. Komatsubara, K. Watanabe and K. Koyama . Magnetic anisotropy in intermetallic compounds containing both Uranium and 3d-metal . Phys. Metals and Metallography114 727 - 733 2013年7月査読

T. Shigeoka, T. Fujiwara, K. Koyama, S. Kimura and K. Watanabe . Multi-step metamagnetic processes of PrPd2Si2 single crystal . J. Korean Phys. Soc.63 567 - 570 2013年7月査読

Y. Adachi, T. Kitai, K. Koyama, H. Yoshika, and T. Kaneko . Magnetization curves of TbZn2 in high magnetic fields . J. Korean Phys. Soc.62 2077 - 2079 2013年7月査読

M. Hiroi, K. Uchida, I. Shigeta, M. Ito and K. Koyama . Antiferromagnetic transition in Ru2CrSi in magnetic fields . J. Korean Phys. Soc.62 2068 - 2072 2013年7月査読

D. Shimada, H. Orihashi, D. Mitsunaga, M. Ito, M. Hiroi, K. Koyama, R. Onodera, K. Takahashi, K. Matsubayashi, Y. Uwatoko . Magnetic properties of Mn2Sb1-xGex (0.05 ? x ? 0.2) in high magnetic fields . J. Korean Phys. Soc.62 747 - 750 2013年7月査読

X. Xu, T. Kihara, M. Tokunagam, A. Matsuo, W. Ito, R.Y. Umetsu, K. Koyama, R. Kainuma . Thermal transformation arrest phenomenon in the metamagnetic shape memory alloys . ICFSMA’13 The Fourth International Conference on Ferromagnetic Shape Memory Alloys, Conference Proceedings 26 - 27 2013年6月

H. Orihashi, M. Hiroi, Y. Mitsui, K. Takahashi, K. Watanabe, K. Matsubayashi, Y. Uwatoko and K. Koyama, . Magnetic and Structural Properties of Mn1.8Co0.2Sb under High Magnetic Fields . Mater. Trans.54 ( 6 ) 969 - 973 2013年6月査読

T. Sakon, K. Koyama, O. Kamiya, S. Awaji, S. Nakamura, T. Nojima, H. Nojiri, K. Watanabe, and M. Hiroi . High-field magnetization measurements of Fe2MnSi . J. Phys. Soc. Jpn.82 ( 4 ) 44802 - -4 2013年4月査読

S. Kimura, K. Okunishi, M. Hagiwara, K. Kindo, Z. He, T. Taniyama, M. Itoh, K. Koyama, and K. Watanabe . Collapse of Magnetic Order of the Quasi One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8 in Transverse Fields . J. Phys. Soc. Jpn82 ( 3 ) 33706 - -4 2013年3月査読

K. Koyama, K. Watanabe, O. Tegus, E. Bruck, K.H.J. Buschow, F.R. de Boer . X-Ray Powder Diffraction Studies on MnFeP0.78Ge0.22 in High Magnetic Fields . J. Low Temp. Phys.170 ( 42130 ) 279 - 284 2013年3月査読

Y. Mitsui, K. Koyama and K. Watanabe . Bi-Mn Binary Phase Diagram in High Magnetic Fields . Mater. Trans.54 ( 2 ) 242 - 245 2013年2月査読

R. Onodera, S. Kimura, K. Watanabe, S. Lee, Y. Yokoyama, A. Makino and K. Koyama . Magnetic Field Effects on Crystallization of Iron-Based Amorphous Alloys . Mater. Trans.54 ( 2 ) 188 - 191 2013年2月査読

R.Y. Umetsu, D. Kikuchi, K. Koyama, K. Watanabe, Y. Yamaguchi, R. Kainuma, T. Kanomata . Site occupancy and magnetic moment of Fe in Ni2Mn0.3Fe0.7Ga alloy by neutron powder diffraction study . J. Alloy. Comp.580 ( 7 ) 506 - 511 2013年1月査読

I. Shigeta, Y. Sakuraba, S. Kimura, K. Koyama, K. Watanabe, K. Takanashi, and M. Hiroi, . Transport and magnetic properties of fully-epitaxial superconducting NbN/half-metallic Heulser alloys Co2MnSi bilayer films . J. Magn. Soc. Jpn37 222 - 226 2013年1月査読

Amitani H., Asakawa A., Ogiso K., Nakahara T., Ushikai M., Haruta I., Koyama K.I., Amitani M., Cheng K.c., Inui A. . The role of adiponectin multimers in anorexia nervosa . Nutrition29 ( 1 ) 203 - 206 2013年1月

記述言語：日本語出版者・発行元：Nutrition

Objective: Anorexia nervosa (AN) continues to be a refractory disease because of its unknown pathogenesis. The role of adiponectin in AN has not been clarified. Moreover, few reports have described the relations between adiponectin isoforms and AN in the physical and psychological states. Therefore, we measured plasma adiponectin and its isoforms levels in patients with AN to examine their roles in AN. Methods: Eighteen women participated in this study: nine patients with AN and nine age-matched healthy controls. We examined plasma adiponectin and its isoforms levels in all subjects and administered three types of psychological test to patients with AN: the Eating Disorders Inventory-2, the Maudsley Obsessional-Compulsive Inventory, and the Beck Depression Inventory-2. Results: We found that the percentage of high-molecular-weight (HMW) to total adiponectin (%HMW) was significantly low and the percentage of low-molecular-weight (LMW) to total adiponectin (%LMW) was significantly high in the AN group compared with the control group. The %HMW positively and the %LMW negatively correlated with body mass index in the entire study population. The %HMW was also positively correlated with psychological symptoms such as social insecurity or cleaning evaluated with the Eating Disorders Inventory-2 or the Maudsley Obsessional-Compulsive Inventory. Conclusions: Our study indicates that all adiponectin isoforms should be evaluated in patients with AN in addition to total adiponectin. The decreased %HMW and the increased %LMW that were correlated with the body mass index and some components of psychopathology in our patients may indicate a complex role of adiponectin isoforms in maintaining energy homeostasis and emotion during extreme malnourishment. © 2013 Elsevier Inc.

DOI： 10.1016/j.nut.2012.07.011

K. Watanabe, Y. Mitsui, K. Koyama . Heat-treatment processing for MnBi in high magnetic fields . Advances in Science and Technology78 19 - 24 2013年査読

重田出, 桜庭裕弥, 木村尚次郎, 小山佳一, 渡辺和雄, 高梨弘穀, 廣井政彦 . 26aKF-1 ハーフメタル型ホイスラー合金/超伝導体接合の輸送特性 III(スピントロニクス(スピン流),領域3(磁性,磁気共鳴)) . 日本物理学会講演概要集68.2.3 ( 0 ) 399 2013年

Goto J., Kakimoto T., Fujii S., Koyama K. . Magnetic and electronic structures of cobalt or copper substituted mn . MATERIALS TRANSACTIONS54 ( 12 ) 2309 - 2312 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

First-principles total-energy calculations have been performed for the hypothetical case of x = 1 in Mn2-xXxSb (X = Co and Cu) for several magnetic states using the full-potential linearized augmented plane wave method based on the generalized gradient approximation. The calculated total energy indicates that the Co (Cu) atom prefers the site Mn(I) to the site Mn(II) (Mn(II) to Mn(I)). This result of Co is consistent with the available neutron diffraction experiment. For CoMnSb where Co occupies the site Mn(I) the change of lattice constants (a and c) and c/a from AF2 to F is in good agreement with experimental trends. Our results indicate that the optimization of the ratio c/a (lattice distortion) is crucial to determine the most stable magnetic state and that the optimization of the atomic positions of the sites Mn(II) and Sb is also crucial. © 2013 The Japan Society for Technology of Plasticity.

DOI： 10.2320/matertrans.m2013327

Orihashi H., Hiroi M., Mitsui Y., Takahashi K., Watanabe K., Matsubayashi K., Uwatoko Y., Koyama K. . Magnetic and Structural Properties of Mn₁.₈Co₀.₂Sb under High Magnetic Fields . MATERIALS TRANSACTIONS54 ( 6 ) 969 - 973 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

Magnetization, electrical resistivity and X-ray diffraction measurements were carried out for Mn1.8Co0.2Sb with a tetragonal structure in 4.2 ≤ T ≤ 280K and in field B up to 16 T. For B = 0 T, anisotropic structural deformation occurred at Tt ∼ 140K for zero-field cooling (ZFC), accompanied by a first-order magnetic transition from the ferrimagnetic (FRI) to antiferromagnetic (AFM) phases. In this deformation, the lattice parameters a and c changed by δ a/a=+0.15% and by δ c/c = -0.44%, respectively. By applying magnetic fields of 5 T, Tt decreased to 60K with thermal hysteresis of 35 K. The two-phase coexistence of the AFM and residual FRI phases was observed even at 10K for field cooling of 5 T, while a single phase of AFM was confirmed for ZFC. At B = 16 T, the transition did not occurs. In addition, a field-induced structural deformation was observed, accompanied by the metamagnetic transition just below Tt. The obtained results are discussed from a viewpoint on entropy change for the transition. © 2013 The Japan Institute of Metals and Materials.

DOI： 10.2320/matertrans.m2012415

西迫裕也, 大久保亮成, 春森浩平, 重田出, 梅津理恵, 伊藤昌和, 小山佳一, 貝沼亮介, 廣井政彦 . アンドレーエフ反射法によるハーフメタル型ホイスラー合金Co2MnSiのスピン分極率測定 . 鹿児島大学理学部紀要46 1 - 8 2013年

I. Shigeta, Y. Sakuraba, S. Kimura, K. Koyama, K. Watanabe, K. Takanashi, M. Hiroi . Transport and magnetic properties of fully-epitaxial superconducting NbN/half-metallic Heulser alloy Co2MnSi bilayer films . Transactions of the Magnetics Society of Japan37 ( 3-2 ) 222 - 226 2013年

重田出, 桜庭裕弥, 木村尚次郎, 小山佳一, 渡辺和雄, 高梨弘毅, 廣井政彦 . 27aXA-13 ハーフメタル型ホイスラー合金/超伝導体接合の輸送特性II(27aXA スピントロニクス(ナノ磁性体),領域3(磁性,磁気共鳴)) . 日本物理学会講演概要集68.1.3 ( 0 ) 537 2013年

Mitsui Y., Koyama K., Watanabe K. . Bi–Mn Binary Phase Diagram in High Magnetic Fields . MATERIALS TRANSACTIONS54 ( 2 ) 242 - 245 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

To examine magnetic field effects on the BiMn equilibrium phase, a high-magnetic fields differential thermal analysis (HF-DTA) was performed for fields up to 18 T and temperatures ranging from 300 to 753 K. For zero field, the peritectic temperatures Tp1 (BiMn1.08 + Bi-rich liquid → BiMn) and Tp2 (αMn + Bi-rich liquid → BiMn 1.08), and the eutectic temperature TE (the Bi-rich liquid → Bi solid + BiMn) were determined to be 632, 721 and 538 K, respectively. The BiMn phase diagram at 18 T was obtained, which showed that Tp1 increases with increasing magnetic fields at the rate of 2KT-1. Furthermore, the liquidus boundary temperature Tliq between BiMn1.08 + liquid and Bi-rich liquid was found to increase nonlinearly with increasing magnetic field. © 2013 The Japan Institute of Metals.

DOI： 10.2320/matertrans.m2012310

J.A. Monroe, I. Karaman, B. Basaran, W. Ito, R.Y. Umetsu, R. Kainuma, K. Koyama, Y.I. Chumlyakov . Direct measurement of large reversible magnetic-field-induced strain in Ni-Co-Mn-In metamagnetic shape memory alloys . Acta Materialia60 ( 20 ) 6883 - 6891 2012年12月査読

Inomata T., Matsukawa M., Kimura D., Yamato Y., Kobayashi S., Suryanarayanan R., Nimori S., Koyama K., Takahashi K., Watanabe K., Kobayashi N. . Suppression of the low-temperature phase-separated state under pressure in (Eu <inf>1-x</inf>Gd <inf>x</inf>) <inf>0.6</inf>Sr <inf>0.4</inf>MnO <inf>3</inf> (x = 0, 0.1) . Journal of Magnetism and Magnetic Materials324 ( 22 ) 3863 - 3869 2012年11月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

We have demonstrated the effect of pressure on the steplike metamagnetic transition and its associated magnetostriction in (Eu 1-xGd x) 0.6Sr 0.4MnO 3 (x=0 and 0.1). The critical field initiating the field induced ferromagnetic transition in both samples is lowered by the applied pressure. The further application of external pressure up to 1.2 GPa on the x=0 parent sample causes a spontaneous ferromagnetic transition with a second-order like character, leading to collapses of the steplike transition and its concomitant lattice striction. These findings indicate a crucial role of the low-temperature phase separated state characterized by a suppressed magnetization upon decreasing temperature. © 2012 Elsevier B.V.

DOI： 10.1016/j.jmmm.2012.06.036

K. Koyama, Y. Mitsui, E.S. Choi, Y. Ikehara, E. Palm, and K. Watanabe . Controlled Equilibrium State of Ferromagnetic MnBi by High Magnetic Fields . Proceedings of the 22nd International Workshop on Rare-Earth Permanent Magnets and their Applications, (Nagasaki, 2012) 110 - 113 2012年9月

T. Inomata, M. Matsukawa, D. Kimura, Y. Yamato, S. Kobayashi, R. Suryanarayanan, S. Nimori, K. Koyama, K. Takahashi, K. Watanabe, N. Kobayashi . Suppression of the low-temperature phase-separated state under pressure in (Eu1-xGdx)0.6Sr0.4MnO3 (x= 0, 0.1) . J. Magn. Magn. Mater.324 3863 - 3869 2012年7月査読

折橋広樹、満永大輔、廣井政彦、三井好古、高橋弘紀、渡辺和雄、小山佳一 . 強磁場 X 線回折実験による Mn1.8Co0.2Sb の磁場中結晶評価 . 日本金属学会誌76 ( 4 ) 246 - 250 2012年4月査読

S. Ebisu, K. Koyama, T. Horikoshi, M. Kokita, S. Nagata . Extremely broad hysteresis in the magnetization process of α-Dy <inf>2</inf>S<inf>3</inf> single crystal induced by high field cooling . Journal of Physics: Conference Series400 ( PART 3 ) 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Journal of Physics: Conference Series

α-Dy2S3 possesses orthorhombic crystal structure having two crystallograpically inequivalent Dy sites. Magnetization process of α-Dy2S3 single crystal after cooling in the high magnetic field of 18 T has been investigated. The magnetization under the field of 18 T along the α-axis on the cooling process from 150 K shows step-like rises at 70 and 40 K and reaches about 9 μB per one Dy3+ at 1.5 K. This value, which corresponds to 90 % of full saturation moment of Dy3+, is much larger than 6 μB obtained at the same conditions after cooling in no magnetic field (zero-field cooling; ZFC). After cooling to 1.5 K, the magnetization while decreasing field shows abrupt drops at 3.0 and 1.7 T, and then comes to 0 μB at 0 T. Subsequently, while increasing field, the magnetization demonstrates a similar curve to that obtained after ZFC without step-like rise below 13.1 T. At μ0H = 13.1 T, the magnetization rises suddenly and agrees with the curve for the decreasing process. This irreversible magnetization process yields extremely broad hysteresis having width of μ0ΔH = 11.4 T. Broader hysteresis and narrower one are also observed at 4.2 and 10 K, respectively.

DOI： 10.1088/1742-6596/400/3/032010

折橋広樹, 満永大輔, 廣井政彦, 三井好古, 高橋弘紀, 渡辺和雄, 小山佳一 . 強磁場 X 線回折実験による Mn1.8Co0.2Sb の磁場中結晶評価 . 日本金属学会誌76 ( 4 ) 246 - 250 2012年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本金属学会

Measurements of magnetization, electrical resistivity and high field X-ray powder diffraction (XRD) were carried out for polycrystalline Mn 1.8Co 0.2Sb in magnetic fields up to 5 T in 4.2-300 K temperature range, in order to investigate the structural properties affected by magnetic fields. In a zero field, the compound shows the first-order magnetic transition from the ferrimagnetic (FRI) to antiferromagnetic (AFM) states at T t = 145 K with decreasing temperature. By applying magnetic fields of 5 T, T tdecreased to 60 K with thermal hysteresis of 35 K. From the XRD measurements, not only the AFM phase but also the residual FRI phase was confirmed even at 10 K in cooling process under 5 T. Results obtained indicate that the residual FRI phase is kinetically arrested. © 2012 The Japan Institute of Metals.

DOI： 10.2320/jinstmet.76.246

Y. Mitsui,K. Koyama,K. Takahashi, and Kazuo Watanabe . Development of an x-ray diffraction camera used in magnetic fields up to 10 T . Rev. Sci. Instrum.82 125104(1) - 125104(6) 2011年12月査読

廣井政彦、小山佳一、伊藤昌和、重田出 . ヘリウム液化装置 . 鹿児島大学理学部紀要44 27 - 32 2011年12月

Ito M., Nagi Y., Kado N., Urakawa S., Ogawa T., Kondo A., Koyama K., Watanabe K., Kindo K. . Magnetic properties of spinel FeCr<inf>2</inf>S<inf>4</inf> in high magnetic field . Journal of Magnetism and Magnetic Materials323 ( 24 ) 3290 - 3293 2011年12月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Magnetism and Magnetic Materials

We studied temperature and magnetic field dependence of magnetization, M(T) and M(B), on thiospinel FeCr2S4. We observed a step-like anomaly at TOO∼9K for M(T) attributed to an orbital order transition in magnetic field 0 <B≤7T. Furthermore, also for M(B), the step-like anomaly appears at Bc∼5.5T below TOO. This suggests an existence of a magnetic phase boundary at Bc in T<TOO. Because the anomaly at Bc of M(B) exists in the orbital ordered phase, the spin structure of FeCr2S4 in T<TOO is strongly coupled with the lattice of the system. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2011.07.041

K. Oikawa, Y. Mitsui, K. Koyama, K. Anzai . Thermodynamic Assessment of the Bi-Mn System . MATERIALS TRANSACTIONS52 ( 11 ) 2032 - 2039 2011年11月査読

M. Yamamoto, S. Sekida, T. Fukuda, T. Kakeshita, K. Takahashi,K. Koyama, H. Nojiri . A new type of FCT martensite phase in single-crystalline Fe(3)Pt Invar alloy . JOURNAL OF ALLOYS AND COMPOUNDS509 ( 34 ) 8530 - 8533 2011年8月査読

Yamamoto M., Sekida S., Fukuda T., Kakeshita T., Takahashi K., Koyama K., Nojiri H. . A new type of FCT martensite phase in single-crystalline Fe<inf>3</inf>Pt Invar alloy . Journal of Alloys and Compounds509 ( 34 ) 8530 - 8533 2011年8月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Alloys and Compounds

Martensitic transformation in a highly ordered Fe3Pt has been investigated by magnetization and X-ray diffraction measurements. We confirmed that a new type of face-centered tetragonal (FCT) martensite phase appears below 60 K in Fe3Pt with a degree of order S = 0.88. The tetragonality c/a gradually increases with decreasing temperature, and is approximately 1.005 at 10 K. This is in contrast to the tetragonality c/a < 1 generally observed in the FCT martensite with a degree of order less than 0.8. The spontaneous magnetization increases in association with the transformation. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2011.06.035

H. Kato,K. Koyama, K. Takahashi . Crystallization of Nd-Co-B nanocomposite ribbons in high magnetic fields . JOURNAL OF APPLIED PHYSICS109 ( 7 ) 07A726 2011年4月査読

Y. Murano, M. Matsukawa, S. Ohuchi, S. Kobayashi, S. Nimori, R. Suryanarayanan, K. Koyama, N. Kobayashi . Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite CaMn1-xSbxO3 . Phys. Rev. B 83 ( 5 ) 54437 - -13 2011年2月査読

K. Koyama, Y. Mitsui, E.S. Choi, Y. Ikehara, E.C. Palm, K. Watanabe . Change of the equilibrium state of ferromagnetic MnBi by high magnetic fields . J. Alloys. Comp.509 L78 - L80 2011年1月査読

R.Y. Umetsu K. Ito, K. Koyama, T. Kanomata, K. Ishida and R. Kainuma, . Kinetic arrest behavior in martensitic transformation of NiCoMnSn metamagnetic shape memory alloy . J. Alloys and Comp.509 1389 - 1393 2011年1月査読

M. Ito, Y. Nagi,N. Kado, S. Urakawa,T. Ogawa, A. Kondo,K. Koyama, K. Watanabe, K. Kindo . Magnetic properties of spinel FeCr(2)S(4) in high magnetic field . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS323 ( 24 ) 3290 - 3293 2011年査読

Koshi Takenaka, Takashi Shibayama, Kazuko Asano, Keiichi Koyama . Magnetostructural Correlations in Nitrogen-Deficient Antiperovskite Mn3CuN1-delta . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN79 ( 7 ) 2010年7月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Ferromagnetic shape memory effects of antiperovskite Mn3CuN are markedly altered by nitrogen deficiency. The martensitic transformation occurs at a lower temperature than ferromagnetic ordering for nitrogen-deficient Mn3CuN0.8, although they both occur simultaneously for stoichiometric Mn3CuN. In the martensitic phase, Mn3CuN0.8 contracts in a direction parallel to the magnetic field, in contrast to the expansion observed in Mn3CuN, implying that the easy axis is converted from the longer a axis in Mn3CuN to the shorter c axis in Mn3CuN0.8. The operating magnetic field for magnetostriction drastically decreases for Mn3CuN0.8, suggesting a possible supermagnetostriction around the critical compositional region for the easy-axis conversion.

DOI： 10.1143/JPSJ.79.073706

H Nishihara, Y Furutani, T Wada, T Kanomata, K Kobayashi, R Kainuma, K Ishida, K Koyama, K Watanabe . Hyperfine coupling constant for 59Co estimated from a high-field susceptibility and high-field NMR shift in ferromagnetic Co2TiGa and Co2VGa . J. Phys. Conf. Ser.200 32052 2010年1月査読

K. Takenaka, T. Shibayama, K. Asano and K. Koyama . Magnetostructural Correlations in Nitrogen-Deficient Antiperovskite Mn3CuN1-δ . J. Phys. Soc. Jpn.79 73706 2010年査読

Y.Mitsui, K. Koyama, W. Ito, R.Y. Umetsu, R. Kainuma, K. Watanabe . Observation of Reverse Transformation in Metamagnetic Shape Memory Alloy Ni40Co10Mn34Al16 by High-Field X-Ray Diffraction Measurements . Materials Transactions51 1648 - 1650 2010年査読

M. Fukuhara, H. Yoshida, K. Koyama, A. Inoue, Y. Miura . Superconductivity of Ni-Nb-Zr-H Glassy Alloys with Nanoclusters . J. Nanosci. Nanotech.10 4975 - 4978 2010年査読

K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, K. Takahashi K, and Y. Sasaki . Tohoku High Magnetic Field Research Activities Using Cryogen-Free Superconducting Magnets . J. Low Temp. Phys.159 370 - 373 2010年査読

M. Fukuhara, H. Yoshida, K. Koyama, A. Inoue, and Y. Miura . Electronic transport behaviors of Ni-Nb-Zr-H glassy alloys . J. Appl. Phys.107 33703 2010年査読

T. Shigeoka, T. Fujiwara, K. Koyama, K. Watanabe, and Y. Uwatoko . High Field Metamagnetism of PrRh2Si2 Single Crystal Compound Having Anomalously High NSel Temperature . J. Low Temp. Phys.159 42 - 45 2010年査読

A.V. Andreev, E.A. Tereshina, E. Santava, J. Sebek, K. Koyama, and K. Watanabe . Sublattice contributions to the magnetism of UFe5Al7 and UFe6Al6 . J. Alloys Comp. 492 52 - 55 2010年査読

X. Xu, W. Ito, R.Y. Umetsu, K. Koyama, R. Kainuma, and K. Ishida . Kinetic Arrest of Martensitic Transformation in Ni33.0Co13.4Mn39.7Ga13.9 Metamagnetic Shape Memory Alloy . Mater. Trans.51 469 - 471 2010年査読

P.J. Shamberger, A.B. Pakhomov, K. Koyama, F.S. Ohuchi . Deviation of the magnetization change from the structural phase transition temperature in polycrystalline Ni-Mn-Sn in low magnetic fields . Scripta Materialia63 1161 - 1164 2010年査読

M. Fukuhara, H. Yoshida, K. Koyama, A. Inoue . Magnetic-field-induced Coulomb oscillation in Ni-Nb-Zr-H glassy alloys . Physica B405 3791 - 3794 2010年査読

M. Yamamoto, T. Fukuda, T. Kakeshita, K. Koyama, H. Nojiri . Martensitic transformation in invar Fe3Pt with highly ordered state . Physics Procedia10 117 - 119 2010年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Elsevier B.V.

We have investigated martensitic transformation in a highly ordered Fe 3Pt by X-ray diffraction measurements. We found that a new type of FCT martensite phase appears in Fe3Pt with degree of order S = 0.88. In this martensite phase, the tetragonality c/a of the martensite is approximately 1.005 at 10 K, being different from that of so far known FCT martensite phase with c/a &lt
1.

DOI： 10.1016/j.phpro.2010.11.085

Hiroi M., Rokkaku T., Matsuda K., Hisamatsu T., Shigeta I., Ito M., Sakon T., Koyama K., Watanabe K., Nakamura S., Nojima T., Nakano T., Chen L., Fujiwara T., Uwatoko Y., Manaka H., Terada N. . Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-x Fex CrSi . Physical Review B Condensed Matter and Materials Physics79 ( 22 ) 2009年6月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B Condensed Matter and Materials Physics

The results of a comprehensive study of the structural, magnetic, and magnetotransport properties of the Heusler compounds Ru2-x Fex CrSi are presented. The Fe-rich compounds (x 1.5) exhibit a usual ferromagnetic transition. The Ru-rich compound (x=0.1) does not show ferromagnetism but exhibits a peak in magnetic susceptibility at TN =30K. Nevertheless, specific-heat measurements show that there is no antiferromagnetic transition at TN nor at any other temperatures. With further decreasing temperature strong irreversible behavior occurs below a temperature Tg. It is proposed that these results can be interpreted as successive spin-glass transitions at TN and Tg. The compounds with intermediate x (=0.3 and 0.5) are found to be ferromagnetic. Both the saturation magnetization and the Curie temperature TC increase with increasing x. However, being different from the Fe-rich compounds, hysteresis of the magnetization is observed and this suggests that the ferromagnetism has glassy character. In lower-temperature range fairly large negative magnetoresistance are observed. These results are suggestive of a magnetically inhomogeneous ferromagnetic state, that is, the formation of ferromagnetic clusters. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.79.224423

A. V. Andreev, K. Koyama, E. A. Tereshina, J. Prokleska, K. Watanabe . Magnetoelasticity of (Lu(0.8)Ce(0.2))(2)Fe(17) intermetallic compound . JOURNAL OF ALLOYS AND COMPOUNDS477 ( 1-2 ) 62 - 67 2009年5月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

Study of magnetostriction of (Lu(0.8)Ce(0.2))(2)Fe(17) has been performed by two methods, bulk and microscopic: by the capacitor dilatometer on a single crystal grown by the Czochralski method and by the X-ray powder diffraction. The field-induced transition from the antiferromagnetic to the ferromagnetic state is accompanied by the lattice expansion both in the basal plane and along the c-axis of the hexagonal structure. In addition to the spontaneous linear magnetostriction lambda(s)(a) = 0.8 x 10(-3), lambda(s)(c) = 6.8 x 10(-3) along the a and c axes, respectively, and volume effect omega(s) = 8.4 x 10(-3), a comparable field-induced magnetostriction (lambda(a) = 1.3 x 10(-3), lambda(c) = 3.4 x 10(-3), omega = 6.0 x 10(-3)) is observed in a field of 5T applied along the a-axis. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2008.11.003

H. C. Hsu, F. C. Chou, K. Koyama, K. Watanabe, H. L. Liu . Spin-phonon coupling in antiferromagnetic Bi2 Sr2 CoO6+δ: An infrared reflectance study . Physical Review B - Condensed Matter and Materials Physics79 ( 15 ) 2009年4月査読

記述言語：英語掲載種別：研究論文（学術雑誌）

The ab -plane infrared and optical reflectance of single-crystal Bi2 Sr2 CoO6+δ (0.4<δ<0.5) have been measured over a wide frequency range (50-55000 cm-1) and at temperatures between 20 and 330 K. The room-temperature infrared spectrum displays an insulating characteristic. The optical gap determined from the infrared conductivity (∼0.53 eV) is consistent with thermal activation energy from dc transport measurements. Upon passing through the 265 K antiferromagnetic ordering transition, a softening of the phonon mode near 205 cm-1 correlates well with the temperature-dependent normalized square of the sublattice magnetization. Furthermore, the magnetic-order-induced splitting of the phonon modes at about 238 and 376 cm-1 is observed. Additionally, the phonon mode at about 588 cm-1 exhibits a Fano-type line shape. Since no appreciable structural change was detected at low temperatures in x-ray diffraction studies, all of these observables suggest a complex nature of spin-phonon coupling in this material. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.79.155109

Y. Yamato, M. Matsukawa, Y. Murano, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 . APPLIED PHYSICS LETTERS94 ( 9 ) 2009年3月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

We report a significant decrease in the low-temperature resistance induced by the application of an electric current on the ab-plane in the paramagnetic insulating (PMI) state of (La0.4Pr0.6)(1.2)Sr1.8Mn2O7. A colossal electroresistance effect attaining -95% is observed at lower temperatures. A colossal magnetoresistive step appears near 5 T at low temperatures below 10 K, accompanied by an ultrasharp width of the insulator-metal transition. Injection of higher currents to the crystal and magnetic field cooling process cause a disappearance of the steplike transition. These findings have a close relationship with the presence of the short-range charge-ordered clusters pinned within the PMI matrix of the crystal studied.

DOI： 10.1063/1.3095598

Yoshifuru Mitsui, Keiichi Koyama, Kazuo Watanabe . X-ray diffraction measurements in high magnetic fields and at high temperatures . SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS10 ( 1 ) 2009年3月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATL INST MATERIALS SCIENCE

A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.

DOI： 10.1088/1468-6996/10/1/014612

Y. Furutani, H. Nishihara, T. Kanomata, K. Kobayashi, R. Kainuma, K. Ishida, K. Koyama, K. Watanabe, T. Goto . Field-induced-moment nuclear coupling for 59Co in a Heusler alloy Co2TiGa . J. Phys.. Conf. Ser.150 42037 - -4 2009年1月査読

Yoshifuru Mitsui, Keiichi Koyama, Yuko Nakamori, Shin-ichi Orimo, Kazuo Watanabe . Magnetic and Structural Phase Transitions in Ferromagnetic MnBi . JOURNAL OF THE JAPAN INSTITUTE OF METALS73 ( 1 ) 40 - 45 2009年1月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN INST METALS

X-ray powder diffraction, magnetization measurements, and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in zero magnetic field as will as in magnetic fields of up to 14 T and in the temperatures range of 300-773 K, in order to investigate magnetic phase transition. In zero magnetic field, a magnetic phase transition from ferromagnetic to paramagnetic state is exhibited at temperature (T-t) of 628 K, accompanied by decomposition. With increasing magnetic field up to 14 T, T-t increases linearly with the rate of 2 KT-1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T-t The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in the interval of 626-623 K, which relates to the metamagnetic transition. The obtained results are discussed on the basis of a mean field theory.

DOI： 10.2320/jinstmet.73.40

R.Y. Umetsu, W. Ito, K. Ito, K. Koyama, A. Fujita, K. Oikawa, T. Kanomata, R. Kainuma, K. Ishida . Anomaly in entropy change between parent and martensite phases in the Ni50Mn34In16 Heusler alloy . Scripta Materialia60 25 - 28 2009年査読

三井好古、小山佳一、中森裕子、折茂慎一、渡辺和雄 . 強磁場下における強磁性体MnBiの相転移 . 日本金属学会誌73 40 - 45 2009年査読

三井好古、小山佳一、渡辺和雄 . 強磁場・高温X線回折測定用試料電気炉の性能評価 . J. Magn. Soc. Jpn.33 60 - 63 2009年査読

K. Koyama, Y. Mitsui, K. Tahashi and K. Watanabe . X-ray powder diffraction camera for high-field experiments . J. Phys.: Conf. Ser.156 12018 2009年査読

K. Koyama, R. Sakakura and K. Watanabe . Development of an extraction type magnetometer under low temperature and high magnetic fields over 20 T by the hybrid magnet . J. Phys.: Conf. Ser.156 12019 2009年査読

Y. Mitsui, K. Koyama and K. Watanabe . X-ray diffraction measurements in high magnetic field and at high temperatures . Sci. Technol. Adv. Mater.10 14612 2009年査読

T. Akiya, H. Kato, M. Sagawa and K. Koyama . Enhancement of coercivity in Al and Cu added Nd-Fe-B sintered magnets by high field annealing . IOP Conf. Ser.: Mat. Sci. Eng.1 12034 2009年査読

Y. Yamato, M. Matsukawa, Y. Murano, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7 . Appl. Phys. Lett.94 92507 2009年査読

Y. Yamato, M. Matsukawa, S. Nimori, R. Suryanarayanan, Y. Murano, Y. Nakanishi, M. Apostu, A. Revcolevschi, K. Koyama, and N. Kobayashi . Effect of pressure on Lattice distortion, transport and magnetic properties of Pr-substituted La1.2Sr1.8Mn2O7 bilayered manganite . J. Phys.: Condens Matter21 486001 2009年査読

H.C. Hsu, F.C. Chou, K. Koyama, K. Watanabe and H.L. Liu . Spin-phonon coupling in antiferromagnetic Bi2Sr2CoO6+δ: An intrared reflectance study . Phys. Rev. B79 155109 2009年査読

M. Hiroi M, T. Rokkaku, K. Matsuda, T. Hisamatsu, I. Shigeta, M. Ito, T. Sakon, K. Koyama, K. Watanabe, S. Nakamura, T. Nojima, T. Nakano, L. Chen, T. Fujiwara, Y. Uwatoko, H. Manaka, and N. Terada . Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-xFexCrS . Phys. Rev. B79 224423 2009年査読

A.V. Andreev, K. Koyama, E.A. Tereshina, J. Prokleska, and K. Watanabe . Magnetoelasticity of (Lu0.8Ce0.2)2Fe17 intermetallic compound . J. Alloys and Compounds477 62 - 67 2009年査読

T Kawamata, N Sugawara, M Uesaka, N Kaneko, T Kajiwara, H Yamane, K Koyama, K Kudo, N Kobayashi, Y Koike . Single-Crystal Growth of Pb2V3O9 and the Bose-Einstein Condensed State of Triplons Studied by Thermal Conductivity, Specific Heat and Magnetization Measurements . J. Phys.: Conf. Ser.150 42087 2009年査読

Y. Yamato, Y. Nakanishi, M. Matsukawa, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Anomalous pressure effect on steplike magnetostriction of (La0.4Pr0.6)(1.2) Sr1.8Mn2O7 bilayered manganese oxide . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We report the pressure effect on a steplike magnetostriction of single crystalline (La0.4Pr0.6)(1.2)Sr(1.8)Mb(2)O(7) bilayered manganite, for our understandings of the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator and to a ferromagnetic metal phase. Application of pressure suppresses a steplike transformation and causes a broad change in the magnetostriction. A delocalization of carriers is promoted with the applied pressure, resulting in the suppressed steplike behaviour. The steplike behaviour observed is closely related to the existence of localized carriers.

DOI： 10.1088/1742-6596/150/4/042121

S. Ebisu, K. Koyama, H. Omote, S. Nagata . High field magnetization processes in single crystals of α-Tb <inf>2</inf>S<inf>3</inf> and α-Dy<inf>2</inf>S<inf>3</inf> . Journal of Physics: Conference Series150 2009年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Rare earth sesquisulfides α-Tb2S3 and α-Dy2S3 possess orthorhombic crystal structure having two independent rare earth sites. High field magnetization processes for single crystals of these compounds have been investigated up to μoH 18 T. Some step-like transitions have been observed in both compounds. The magnetization of α-Tb2S3 single crystal under the field along the 6-axis at T 1.4 K shows a steep increase of about 4.5 μB, which corresponds to a half of full saturation moment of free Tb3+, at μoH 2.2 T. It is considered that the reorientation of Tb3+ moments on only one Tb site into a ferromagnetic arrangement occurs. When the magnetic field is perpendicular to the b-axis, one-step transition at μoH 0.7 T for Hc and two-step transitions at 0.7 and 1.2 T for Ha are observed. As for α-Dy 2S3, the magnetization curve at T 1.5 K shows two-step transitions at 1.3 and 1.6 T (Hb), three or four dull steps (Ha or c). The total height of two steps in the M-H curve for Hb corresponds to a half of full Dy3+ moment. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/150/4/042027

Y. Furutani, H. Nishihara, T. Kanomata, K. Kobayashi, R. Kainuma, K. Ishida, K. Koyama, K. Watanabe, T. Goto . Field-induced-moment nuclear Coupling for Co-59 in a Heusler alloy Co2TiGa . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

The positive hyperfine field at Co nucleus in a Heusler alloy Co2TiGa is discussed to be not dominated by the orbital hyperfine field from a quite different point of view from former studies. Field-induced-moment nuclear coupling for Co-59 via spin-orbit interaction on Co atom in Co2TiGa is discussed to be small from the observed high-field shift of the NMR of Co-59 in the ferromagnetic state of only +0.83 % in contrast to the case of CoCl2 center dot 2H(2)O with +29%.

DOI： 10.1088/1742-6596/150/4/042037

H. Okada, Y. Kusakari, E. Matsuoka, H. Onodera, K. Koyama, K. Watanabe, T. Kanomata . Transport properties of Heusler compounds Ru2CrGe and Ru2CrSn under high magnetic fields . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We have performed the specific heat and the electrical resistivity measurements under high magnetic fields for Heusler compounds Ru2CrGe and Ru2CrSn. We found that the electrical resistivity for Ru2CrGe shows an upturn in the vicinity of 130 K and changes a metallic to a semiconducting-like behavior with decreasing temperature. By applying magnetic field, a negative magnetoresistance was observed below 200 K. On the other hand, the electrical resistivity for Ru2CrSn shows a semimetallic-like behavior. The results of the electrical resistivity in Ru2CrGe suggest that the compound has a gap-like structure in the electronic structure at the Fermi level. Moreover, it was found that another phase transition occurs in Ru2CrGe and Ru2CrSn, in addition to the magnetic transition.

DOI： 10.1088/1742-6596/150/4/042153

E. G. Gerasimov, N. V. Mushnikov, K. Koyama, T. Kanomata, K. Watanabe . Positive magnetoresistance and large magnetostriction at first-order antiferro-ferromagnetic phase transitions in RMn(2)Si(2) compounds . JOURNAL OF PHYSICS-CONDENSED MATTER20 ( 44 ) 2008年11月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

The magnetostriction and magnetoresistance associated with the field-induced and spontaneous first-order antiferro-ferromagnetic (AF-F) phase transitions have been studied for quasi-single-crystalline samples of La(0.25)Sm(0.75)Mn(2)Si(2), La(0.25)Y(0.75)Mn(2)Si(2) and La(0.27)Y(0.73)Mn(2)Si(2) compounds with natural layered ThCr(2)Si(2)-type structure. It was found that both the spontaneous and field-induced AF-F transitions are accompanied by a large volume magnetostriction Delta V/V approximate to 2 x 10(-3) and anisotropic linear changes of the lattice parameters Delta a/a approximate to 1.6 x 10(-3), Delta c/c approximate to -0.75 x 10(-3). The field-induced AF-F magnetic phase transition has been observed in magnetic fields applied both along the c-axis and in the basal plane, and the magnetostriction value is virtually independent of the direction of applied field. It has been found also that the magnetoresistance is positive in these compounds (the value of the electrical resistance in the ferromagnetic state is higher than that in the antiferromagnetic state) for the fields applied both along the c-axis and in the basal plane. The value of the magnetoresistance observed along the c-axis is 30 times as high as that in the basal plane. The obtained results indicate that the electronic band structure changes are likely responsible for the AF-F magnetic phase transitions observed in the RMn(2)X(2) compounds.

DOI： 10.1088/0953-8984/20/44/445219

Y. Yamato, M. Matsukawa, T. Kumagai, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Effect of pressure on the steplike magnetostriction of single crystalline bilayered manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7) . PHYSICAL REVIEW B78 ( 13 ) 2008年10月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report the effect of pressure on the steplike magnetostriction of single crystalline bilayered manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7), for our understanding of the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase. The application of pressure suppresses a steplike transformation and causes a broad change in the magnetostriction. The injection of an electric current to the crystal also weakens the steplike variation in both the magnetostriction and magnetoresistance. The stabilization of ferromagnetic interaction or the delocalization of charge carriers is promoted with the applied pressure or applied current, resulting in the suppressed steplike behavior. Our findings suggest that the step phenomenon is closely related to the existence of localized carriers such as the short-range charge-orbital-ordered clusters.

DOI： 10.1103/PhysRevB.78.132411

T. Fujita, H. Okada, K. Koyama, K. Watanabe, S. Maekawa, M. W. Chen . Unusually Small Electrical Resistance of Three-Dimensional Nanoporous Gold in External Magnetic Fields . PHYSICAL REVIEW LETTERS101 ( 16 ) 2008年10月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report the electric conductivity of three-dimensional (3D) nanoporous gold at low temperatures and in strong magnetic fields. It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be similar to 14 nm. This study underscores the importance of 3D topology of a nanostructure on electronic transport properties and has implications in manipulating electron transport by tailoring 3D nanostructures.

DOI： 10.1103/PhysRevLett.101.166601

Hiroaki Kato, Takahiro Akiya, Kunihiro Koike, Keiichi Koyama, Masato Sagawa . Coercivity enhancement induced by high-magnetic-field annealing in sintered Nd-Fe-B magnets . Proceedings of The 20th Workshop on Rare Earth Permanent Magnets and Applications 2008年9月招待

A. V. Andreev, E. A. Tereshina, E. Santava, I. Satoh, T. Yamamura, Y. Shiokawa, K. Koyama, K. Watanabe . Magnetic properties of U-2(Fe1-xNix)(13.6)Si-3.4 single crystals . JOURNAL OF ALLOYS AND COMPOUNDS461 ( 1-2 ) 6 - 8 2008年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

The concentration evolution of crystal structure, magnetic moment and anisotropy constants in U-2(Fe1-xNix)(13.6)Si-3.4 investigated on single crystals grown by the Czochralski method is found to be similar to that in the previously studied U-2(Fe1-xNix)(13.6)Si-3.4 system, only the Ni solubility is limited by x = 0.3 in difference with unlimited Co solubility. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2007.06.086

M. Ohtsuka, J. Sekino, K. Koyama, T. Takagi, K. Itagaki . Magnetostructural phase transformation and shape memory effect of Fe-added Ni(2)MnGa films . EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS158 173 - 178 2008年5月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER HEIDELBERG

The magnetostructural phase transformation and shape memory effect (SME) of Fe-added Ni(2)MnGa films were investigated. The free-standing films were heat-treated at 1073 K for 3.6 ks and constraint-aged (CA) at various conditions (473 similar to 723 K, 0 similar to 14.4 ks) to make the two-way SME. The reversible two-way SME by the temperature change was confirmed through the martensitic transformation (MT) and its reversion. The gradient of strain-temperature curve, the effective recovery strain and the width of thermal hysteresis were dependent on the CA conditions. The magnetic field (MF) induced structural phase transformation was evaluated by an XRD apparatus in high MF up to 5 T. It was confirmed that the martensitic phase was stabilized by the MF. Furthermore, the SME by the MF was observed around MT temperature on cooling process for the CA film. It was concluded that the MF induced SME appeared by the induction of the MT with MF.

DOI： 10.1140/epjst/e2008-00672-4

K. Koyama, H. Onodera, and K. Watanabe . Magnetization measurements of DyB2C2 under high pressure and high magnetic fields . Physica B403 1607 - 1608 2008年査読

E.G. Gerasimov, N.V. Nushnikov, K. Koyama, T. Kanomata, and K. Watanabe . Positive magnetoresistance and large magnetostriction at first-order antiferro-ferromagnetic phase transitions in RMn2Si2 compounds . J. Phys.: Condens. Matter20 445219 2008年査読

A.V. Andreev, E.A. Tereshina, E. Santava, I. Satoh, T. Yamamura, Y. Shiokawa, K. Koyama, K. Watanabe . Magnetic properties of U2(Fe1-xNix)13.6Si3.4 single crystals . J. Alloys Comp.461 6 - 8 2008年査読

Y. Takahashi, T. Harada, T. Kanomata, K. Koyama, H. Yoshida, T. Kaneko, M. Kataoka . Magnetoresistance effect of pseudobinary compounds Cr1-xRuxSb2 . J. Alloys Comp.459 78 - 82 2008年査読

A.V. Andreev, E.A. Tereshina, E. Santava, K. Koyama, Y. Homma, I. Satoh, T. Yamamura, Y. Shiokawa, K. Watanabe . Magnetic properties of U2Co17-xSix single crystals . J. Alloys Comp.450 51 - 57 2008年査読

T. Sakon, S. Saito, K. Koyama, S. Awaji, I. Sato, T. Nojima, K. Watanabe, M. Motokawa, N.K. Sato . Magnetic anisotropy study of UGe2 in a static high magnetic field . J. Phys.: Conf. Ser. 51 255 - 258 2008年査読

T. Shigeoka, N. Kimura, K. Koyama and K. Watanabe . High field magnetization of TbCu2Si2 single crystal compound . J. Phys.: Conf. Ser51 83 - 86 2008年査読

Y. Makihara, H. Fujii, T. Fujiwara, K. Watanabe, K. Takahashi, K. Koyama and M. Motokawa . Magneto-volume effect in the ground and field induced states of Ce2Fe17 . Physica B329-333 663 - 664 2008年査読

T. Fujiwara, H. Fujii, Y. Uwatoko, K. Koyama, M. Motokawa and T. Shigeoka . Dramatic change of the magnetic characteristics in YbMn2Ge2 under high pressures . Acta Phys. Pol. B (Sp. Iss.)34 1541 - 1544 2008年査読

K. Koyama, T. Goto, T. Kanomata, R. Note and Y. Takahashi . Nonlinear magnetization process of single-crystalline FeSi . J. Phys. Soc. Jpn.69 219 - 224 2008年査読

H. Okada, K. Koyama, M. Nakatake, K. Shimada, H. Namatame, M. Taniguchi, and K. Watanabe . Photoemission spectroscopy of spinel-type CuV2S4 single crystal . J. Phys. Soc. Jpn77 114711 2008年査読

H. Okada, K. Koyama, M. Hedo, Y. Uwatoko, and K. Watanabe . Pressure-induced metal-insulator transition in spinel compound CuV2S4 . Phsica B403 1612 - 1613 2008年査読

Y. Yamato M. Matsukawa, T. Kumagai, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, and N. Kobayashi . Effect of pressure on the steplike magnetostriction of single crystalline bilayered manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7 . Phys. Rev. B78 132411 2008年査読

W. Ito, K. Ito, R.Y. Umetsu, R. Kainuma, K. Koyama, K. Watanabe, A. Fujita, K. Oikawa, K. Ishida, T. Kanomata . Kinetic arrest of martensitic transformation in the NiCoMnIn metamagnetic shape memory alloy . Appl. Phys. Lett.92 21908 2008年査読

K. Takahashi, K. Koyama, and K. Watanabe . 100 mm wide bore cryocooled hybrid magnet for a high field X-ray diffractometer . IEEE trans. Apply. Superconductivity18 536 - 539 2008年査読

T. Fujita, H. Okada, K. Koyama, K. Watanabe, S. Maekawa and M.W. Chen . Unusual Small Electrical Resistance of Three-Dimensional Nanoporous Gold in External Magnetic Fields . Phys. Rev. Lett.101 166601 2008年査読

K. Koyama, Y. Mitsui and K. Watanabe . Magnetic and structural phase transitions of MnBi under high magnetic fields . Sci. Technol. Adv. Mater.9 24204 2008年査読

M. Ohtsuka, J. Sekino, K. Koyama, T. Takagi, and K. Itagaki . Magnetostructural phase transformation and shape memory effect of Fe-added Ni2MnGa films . Eur. Phys. J. Special Topics158 173 - 178 2008年査読

K. Asano, K. Koyama, and K. Takenaka . Magnetostriction in Mn3CuN . Appl. Phys. Lett.92 161909 2008年査読

H. Okada, K. Koyama, K. Watanabe, Y. Kusakari, T. Kanomata, and H. Nishihara . Magnetic properties of Heusler compounds Ru2CrGe and Ru2CrSn . Appl. Phys. Lett. 92 62502 2008年査読

E.A. Tereshina, A.V. Andreev, K. Koyama, K. Watanabe . Magnetostriction at the Metamagnetic Phase Transition in (Lu0.8Ce0.2)2Fe17 . WDS’08 Proceedings of Contributed papers, Part III, 101 - 106 2008年

Makoto Yoshida, Yumiko Kitano, Yuji Inagaki, Takahiro Sakurai, Motoi Kimata, Susumu Okubo, Hitoshi Ohta, Keiichi Koyama, Mitsuhiro Motokawa, Takayuki Asano, Yoshitami Ajiro . Observation of direct transitions in the ferromagnetic and antiferromagnetic dimer system (CH3)(2)NH2CUCl3 by high-field ESR . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN76 ( 11 ) 2007年11月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

High-field electron spin resonance (ESR) measurements of single crystals of (CH3)(2)NH2CuCl3 (DMACuCl(3)) have been performed in the frequency range of 50 to 550 GHz in the paramagnetic region. In addition to the electron paramagnetic resonance, we have observed four ESR modes omega(1), omega(2), omega(3), and omega(4). The modes omega(2) and omega(3) have a frequency gap of 325 GHz (15.6 K), while the mode omega(1) has a gap of 420 GHz (20 K) at 0 T. The modes omega(2) and omega(3) are attributed to the transitions between the singlet and the triplet of the antiferromagnetic (AF) dimer. We found that the large spin-gap for the AF dimer still remains at the critical field B-c2 = 3.5 T determined by magnetization and specific heat measurements.

DOI： 10.1143/JPSJ.76.113704

K. Hachitani, H. Amanuma, H. Fukazawa, Y. Kohori, I. Watanabe, K. Koyama, K. Kumagai, C. Sekine, I. Shirotani . Sm-based Filled Skutterudite Phosphides SmT<inf>4</inf> P<inf>12</inf> (T = Fe, Ru, Os) Studied by 31P-NMR and μSR . Journal of Physics and Chemistry of Solids68 ( 11 ) 2080 - 2083 2007年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The Sm-based filled skutterudite phosphides SmT4 P12 (T = Fe, Ru, Os) have been studied by 31P-NMR (nuclear magnetic resonance) and μSR (muon spin relaxation). The ferromagnetic order and the heavy fermion behavior in SmFe4 P12 and the antiferromagnetic order in SmOs4 P12 were confirmed by 31P-NMR and μSR. In SmRu4 P12, a successive anomaly around the metal-insulator transition temperature and around the Néel temperature was observed by 31P-NMR in high applied magnetic fields. The μSR results of SmRu4 P12 indicate the magnetic order below the metal-insulator transition temperature, which supports the existence of the octupolar order in SmRu4 P12. © 2007.

DOI： 10.1016/j.jpcs.2007.08.033

E. A. Tereshina, A. V. Andreev, K. Koyama, Y. Shiokawa, I. Satoh, K. Watanabe . Magnetic anisotropy and spin reorientation in U2Co15Si2 . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS316 ( 2 ) E515 - E518 2007年9月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Field and temperature dependencies of the magnetization measured along the principal axes of a U2Co15Si2 single crystal show that this compound is a ferromagnet with a spontaneous magnetic moment of 14.8 mu(B) per formula unit (at 4.2 K), located in the basal plane of the hexagonal crystal structure. A strong easy-plane magnetic anisotropy (K-1 = -0.97 MJ m(-3) at 4.2 K) is attributed to the U sublattice because Lu2Co15Si2 exhibits easy-axis anisotropy with K-1 = 0.42 MJ m(-3). The easy-plane anisotropy of U2Co15Si2 transforms to a cone of easy axes above 270 K. The magnetization vector approaches the c-axis at 350 K, and the compound has easy c-axis anisotropy up to the Curie temperature T-C = 601 K. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2007.03.006

A. V. Andreev, K. Koyama, N. V. Mushnikov, V. Sechovsky, Y. Shiokawa, I. Satoh, K. Watanabe . Interplay between effects of external pressure and dilution of the U sublattice in UCoAl-based materials . JOURNAL OF ALLOYS AND COMPOUNDS441 ( 1-2 ) 33 - 38 2007年8月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

Substitution of Y for U in the itinerant 5f-electron metamagnet, UCoAl, transforms the system to a ferromagnetic state. Application of external hydrostatic pressure above 0.3 GPa suppresses the ferromagnetism and restores the "UCoAl-type" metamagnetism back. However, the metamagnetic transition becomes of the second order instead of the first order one in parent UCoAl. This is attributed to enhancement of fluctuations of the U magnetic moment upon dilution of the U sublattice. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2006.09.111

Tetsuya Onogi, Keiichi Koyama, Kazuo Watanabe . Magnetic properties of MnBi in high magnetic fields and high temperature . JOURNAL OF THE JAPAN INSTITUTE OF METALS71 ( 6 ) 489 - 493 2007年6月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN INST METALS

Magnetization measurements of polycrystalline MnBi were carried out in magnetic fields up to 10 T and in the temperature range from 300 to 773 K, in order to clarify the magnetic properties under high magnetic fields and high temperature. The magnetic phase transition temperature (T-c) at a zero magnetic field is 633 K, which almost linearly increases by 2.3 KT-1 with increasing fields up to 10 T. Furthermore, a metamagnetic transition was observed just above T, indicating that the phase transition is first order. The magnetic entropy change is estimated to be 14 J kg(-1) K-1 for 2 T at T-c using Clausius-Clapayron's equation, which is almost constant for magnetic fields up to 10 T.

DOI： 10.2320/jinstmet.71.489

M. Matsukawa, Y. Yamato, T. Kumagai, A. Tamura, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Steplike lattice deformation of single crystalline (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 bilayered manganite . PHYSICAL REVIEW LETTERS98 ( 26 ) 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

We report a steplike lattice transformation of single crystalline (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 bilayered manganite accompanied by both magnetization and magnetoresistive jumps, and examine the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge decrease in resistance. Our findings support that the abrupt magnetostriction is closely related to an orbital frustration existing in the inhomogeneous paramagnetic insulating phase rather than a martensitic scenario between competing two phases.

DOI： 10.1103/PhysRevLett.98.267204

T. Sakon, S. Saito, K. Koyama, S. Awaji, I. Sato, T. Nojima, K. Watanabe, N. K. Sato . Experimental investigation of giant magnetocrystalline anisotropy of UGe2 . PHYSICA SCRIPTA75 ( 4 ) 546 - 550 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

UGe2 is a ferromagnetic heavy-fermion (HF) superconductor, which provides superconductivity under pressure in the range of 1.0 to 1.5 GPa. In this paper, we conducted detailed magnetization experiments up to 27 T and at atmospheric pressure. Magnetization along the a-axis indicates typical ferromagnetic property. On the other hand, magnetization along the b-axis is quite a bit smaller than that of the easy a-axis. The magnetocrystalline anisotropy constant is the same as the rare earth ferromagnet Nd2Fe17, which indicates that UGe2 is a highly anisotropic ferromagnet.

DOI： 10.1088/0031-8949/75/4/030

S. V. Demishev, A. V. Semeno, A. A. Pronin, N. E. Sluchanko, N. A. Samarin, H. Ohta, S. Okubo, M. Kimata, K. Koyama, M. Motokawa, A. V. Kuznetsov . Quantum criticality and collective effects in low-dimensional magnet CuGeO3 : Fe probed by high frequency EPR . JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM20 ( 2 ) 105 - 108 2007年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

For CuGeO3 single crystals doped with 1% of Fe, the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: alpha = 0.34 (B parallel to a and B parallel to c) and alpha = 0.31 (B parallel to b). The description of the temperature dependencies of the line width and g-factor could be obtained in the Oshikawa-Affleck theory assuming that staggered component of the magnetic moment is located predominantly along b-axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.

DOI： 10.1007/s10948-006-0214-3

M. Yoshida, Y. Kitano, Y. Inagaki, T. Sakurai, M. Kimata, S. Okubo, H. Ohta, K. Koyama, M. Motokawa, T. Asano, and Y. Ajiro . Observation of direct transitions in the ferromagnetic and antiferromagnetic dimmer system (CH3)2NH2CuCl3 by high-field ESR . J. Phys. Soc. Jpn76 113704 2007年1月査読

M. Matsukawa, A. Tamura, S. Nimori, R. Suryanarayanan, T. Kumagai, Y. Nakanishi, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Anomalous pressure effect on the remanent lattice striction of a (La,Pr)(1.2)Sr1.8Mn2O7 bilayered manganite single crystal . PHYSICAL REVIEW B75 ( 1 ) 2007年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

We have studied the pressure effect on magnetostriction, both in the ab plane and along the c axis of a (La, Pr)(1.2)Sr1.8Mn2O7 bilayered manganite single crystal over the temperature region where the field-induced ferromagnetic metal (FMM) transition takes place. For comparison, we have also examined the pressure dependence of magnetization curves at the corresponding temperatures. The applied pressure reduces the critical field of the FMM transition and it enhances the remanent magnetostriction. An anomalous pressure effect on the remanent lattice relaxation is observed and is similar to the pressure effect on the remanent magnetization along the c axis. These findings are understood from the viewpoint that the double-exchange interaction-driven FMM state is strengthened by the application of pressure.

DOI： 10.1103/PhysRevB.75.014427

Evgeniya A. Tereshina, Hajime Yoshida, Alexander V. Andreev, Irina S. Tereshina, Keiichi Koyama, Takeshi Kanomata . Magnetism of a Lu<inf>2</inf>Fe<inf>17</inf>H single crystal under pressure . Journal of the Physical Society of Japan76 82 - 83 2007年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）

Lu2Fe17 is a ferromagnet below TC∼140 K and antiferromagnet up to TN=275 K. Hydrogen absorption leads to a stabilization of the ferromagnetism over the whole range of magnetic order and to an increase of the ordering temperature up to TC=354 K in Lu 2Fe17H. The external pressure compensates the lattice expansion upon hydrogenation, and a reentrance of antiferromagnetism is observed. © 2007 The Physical Society of Japan.

DOI： 10.1143/JPSJS.76SA.82

M. Kimata, Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H. M. Yamamoto, R. Kato . Low-temperature Fermi surface of the organic conductor β″ -(BEDT-TTF) (TCNQ)(1-x) (F1-TCNQ)x (x=0,0.05) from magnetooptical measurements . Physical Review B - Condensed Matter and Materials Physics75 ( 4 ) 2007年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Magnetooptical measurements have been performed on the organic conductor β″ -(BEDT-TTF)(TCNQ) (x=0 salt), and a related compound, β″ -(BEDT-TTF)(TCNQ) 0.95 (F1-TCNQ) 0.05 (x=0.05 salt), to investigate their low-temperature Fermi surfaces (FSs). Although the room-temperature FS of both salts can be considered the same, our results indicate that the low-temperature FSs are completely different from each other. In the x=0 salt, the low-temperature FS consists of two very anisotropic quasi-two-dimensional (Q2D) FSs. Cross-sectional areas of anisotropic Q2D-FSs are very small, and correspond to 1-2 % of the first Brillouin zone at room temperature. On the other hand, in the x=0.05 salt, only a pair of quasi-one-dimensional FSs exist at low temperature. Compared with the band calculation of x=0 salt, this Q1D-FS originates from the BEDT-TTF conducting layers. This result indicates that the two hump-like anomalies in the temperature dependence of resistivity at 80 and 20 K, which are observed only in the x=0 salt, are related to the nesting of BEDT-TTF Q1D-FS. Hence, it is considered that anisotropic Q2D-FS pockets observed in the x=0 salt are generated by the imperfect nesting of Q1D-FS, and the density wave state may be formed in the x=0 salt at low temperatures. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.75.045126

Alexander V. Andreev, Keiichi Koyama, Nikolai V. Mushnikov, Vladimir Sechovsky, Yoshinobu Shiokawa, Isamu Satoh, Kazuo Watanabe . Transition from ferromagnetism to metamagnetism under pressure in a uo.94yo.o6coal single crystal . Journal of the Physical Society of Japan76 43 - 46 2007年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）

Substitution of Y for U in the itinerant 5f-electron metamagnet UCoAl transforms the system to a ferromagnetic ground state. Application of external hydrostatic pressure above 0.3 GPa suppresses the ferromagnetism and restores the "UCoAl-type" metamagnetism. However, the metamagnetic transition becomes of the second-order type instead of the first-order one for the parent UCoAl. © 2007 The Physical Society of Japan.

DOI： 10.1143/JPSJS.76SA.43

K. Koyama, S. Miura, H. Okada, T. Shigeoka, K. Watanabe . Magnetic entropy changes of SmMn2Ge2 under high pressure . Mater. Trans.48 451 - 454 2007年査読

K. Hachitani, H. Amanuma, H. Fukazawa, Y. Kohori I. Watanabe, K. Koyama, K. Kumagai, C. Sekine and I. Shirotani . Sm-based filled Skutterudite phosphides SmT4P12 (T=Fe, Ru, Os) studied by 31P-NMR and μSR . J. Phys. Chem. Solid68 2080 - 2083 2007年査読

M. Matsukawa, Y. Yamato, T. Kumagai, A. Tamura, R. Suryanarayanan, S. Nimori, M. Apostu, A. Recolevschi, K. Koyama, and N. Kobayashi . Steplike lattice deformation of single crystalline (La0.4Pr0.6)1.2Sr1.8Mn2O7 bilayered Manganite . Phys. Rev. Lett.98 267204 2007年査読

E.A. Tereshina, A.V. Andreev, K. Koyama, Y. Shiokawa, I. Satoh, and K. Watanabe . Magnetic anisotropy and spin reorientation U2Co15Si2 . J. Magn. Magn. Mater316 e515 - e518 2007年査読

A.V. Andreev, E.A. Tereshina, E. Santava, K. Koyama, Y. Homma, I. Satoh, T. Yamamura, Y. Shiokawa, K. Watanabe . Crystal structure and magnetic properties of U2Co17-xSix single crystals . J. Magn. Magn. Mater.310 e598 - e600 2007年査読

A. Himori, M. Tanaka, K. Koyama, K. Watanabe and T. Shigeoka . Magnetic behavior of TbRh2Si2 single crystal . J. Magn. Magn. Mater.310 1770 - 1772 2007年査読

T. Sakon, S. Saito, K. Koyama, S. Awaji, I. Sato, T. Nojima, K. Watanabe and N.K. Sato . Experimental investigation of giant magnetocrystaline anisotropy of UGe2 . Phys. Scr.75 546 - 550 2007年査読

M. Matsukawa, A. Tamura, S. Nimmori, R. Suryanarayanan, T. Kumagai, Y. Nakanishi, M. Apostu, A. Revcolevschi, K. Koyama, and N. Kobayashi . Anomalous pressure effect on the remanent lattice striction of a (La, Pr)1.2Sr1.8Mn2O7 bilayered manganite single crystal . Phys. Rev. B75 14427 2007年査読

A.V. Andreev, K. Koyama, N.M. Mushnikov, V. Sechovsky, Y. Shiokawa, I. Satoh, and K. Watanabe . Interplay between effects of external pressure and dilution of the U-sublattice in UCoAl-base materials . J. Alloys Comp.441 33 - 38 2007年査読

O. Tegus, K. Koyama, J.L. Her, K. Watanabe, E. Bruck, K.H.J. Buschow, F.R. de Boer . X-ray diffraction on MnFeP0.46As0.54 in a magnetic field . Physica B392 151 - 153 2007年査読

K. Wang, T. Fujita, M.W. Chen, T.G. Nieh, H. Okada, K. Koyama, W. Zhang and A. Inoue . Electrical conductivity of a bulk metallic glass composite . Appl. Phys. Lett.91 154101 2007年査読

H. Kato, T. Akiya, M. Sagawa, K. Koyama and T. Miyazaki . Effect of high magnetic field on the coercivity in sintered Nd-Fe-B magnets . J. Magn. Magn. Matter.310 2596 - 2598 2007年査読

K. Koyama, T. Onogi, Y. Mitsui, Y. Nakamoi, S. Orimo, and K. Watanabe . Magnetic phase transition of MnBi under high magnetic fields and high temperature . Mater. Trans.48 2414 - 2418 2007年査読

小野木哲也、小山佳一、渡辺和雄 . 一次相転移物質MnBi の高温・強磁場磁気特性 . 日本金属学会誌71 489 - 493 2007年査読

K. Koyama, T. Iagarashi, H. Okada, K. Watanabe, T. Kanomata, R. Kainuma, W. Ito, K. Oikawa, K. Ishida . Magnetic and thermoelectric properties of Ni50Mn36Sn14 in high magnetic fields . J. Magn. Magn. Mater.310 e994 - e995 2007年査読

M. Kimata, Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto, and R. Kato . Low-temperature Fermi surface of the organic conductor β”-(BEDT-TTF)(TCNQ)(1-x)(F1-TCNQ)x (x=0, 0.05) from magnetooptical measurements . Phys. Rev. B75 45126 2007年査読

Kenichi Hachitani, Hideaki Amanuma, Hideto Fukazawa, Yoh Kohori, Keiichi Koyama, Ken-ichi Kumagai, Chihiro Sekine, Ichimin Shirotani . Appearance of successive phase transition in SmRU4P12 under high magnetic fields probed by P-31 nuclear magnetic resonance . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN75 ( 12 ) 2006年12月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The P-31-NMR (nuclear magnetic resonance) measurements of the filled skutterudite SmRu4P12 have been carried out in several applied magnetic fields. The line width of the P-31-NMR spectrum rapidly increases below the metal-insulator transition temperature T-MI, which indicates the appearance of an internal field below the temperature. Though no distinct anomaly was observed below T-MI in low fields, a complicated structure was observed between the Neel temperature T-N and T-MI (T-N < T-MI) above 70 kOe. The spin-lattice relaxation rate l/T-1 is almost independent of temperature above T-MI, and rapidly decreases below T-MI. The l/(T1) in low fields decreases monotonously, whereas the strong suppression of l/(T1) occurs between T-N and T-MI above 70 kOe. The structure of the spectra and the suppression of l/T-1 become apparent with increasing field.

DOI： 10.1143/JPSJ.75.124712

J Prchal, H Kitazawa, T Furubayashi, P Javorsky, K Koyama, Sechovsky, V . Low-temperature structural study of the TbPd1-xNixAl series . PHYSICA B-CONDENSED MATTER378-80 1102 - 1104 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

A discontinuity in the temperature dependence of the lattice parameters while preserving the crystal symmetry was observed for TbPdAl, TbNiAl and TbPd0.9Ni0.1Al. We associate this result with the previously reported step-like change in the concentration dependence of lattice parameters in RE(Ni1-xCux)Al pseudo-ternary compounds. Our results corroborate the scenario for the RTX compounds with the ZrNiAl-type structure based on existence of a narrow interval of forbidden c/a values. For TbPdAl, TbNiAl and TbPd0.9Ni0.1Al we observed also a certain temperature interval of coexistence of two ZrNiAl-type phases characterized by two distinctly different c/a values. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.437

K Yagasaki, S Notsu, Y Takaesu, T Nakama, E Sakai, K Koyama, K Watanabe, AT Burkov . X-Ray diffraction on rare earth-3d Laves phase compound ErCo2 in magnetic field . PHYSICA B-CONDENSED MATTER378-80 1089 - 1090 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

X-Ray powder diffraction method is used to investigate the effect of magnetic ordering and external magnetic field on crystal structure of Laves phase intermetallic compound ErCo2. The diffraction patterns were recorded at temperatures from 300 K down to 8.5 K in magnetic field up to 5 T. Distortion of the room-temperature cubic structure was found in magnetically ordered state below 32 K. The symmetry at low temperature is rhombohedral in agreement with literature results. Or lower symmetry than it. However the symmetry of the unit cell increases to cubic in external magnetic field of 5 T. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.514

Kazuo Watanabe, Asaya Fujita, Keiichi Koyama . Special issue on Research on New Magnetic Properties and Applications to Materials Science in Itinerant-Electron Systems - Preface . MATERIALS TRANSACTIONS47 ( 3 ) 455 - 455 2006年3月査読

M. Kimata, Y. Oshima, K. Koyama, H. Ohta, M. Motokawa, H. Nishikawa, K. Kikuchi, I. Ikemoto . Detailed fermi surface topology of the quasi-one-dimensional conductor (DMET)(2)I-3 . JOURNAL OF LOW TEMPERATURE PHYSICS142 ( 3-4 ) 523 - 526 2006年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER/PLENUM PUBLISHERS

The detailed topology of the Fermi surface of the quasi-one-dimensional conductor (DMET)(2)I-3 was investigated by the magnetooptical measurements. A pair of planar Fermi surface which has higher corrugations of Fourier components was observed. This result seems to suggest that the metallic state of this salt is stabilized by the higher corrugations of the Fermi surface.

DOI： 10.1007/s10909-006-9159-y

H Okada, K Koyama, M Yamada, T Goto, Y Makihara, H Fujii, K Watanabe . Magnetic properties of Ce(Fe1-xCox)(2) under high pressure . JOURNAL OF ALLOYS AND COMPOUNDS408 144 - 146 2006年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

We have studied the magnetic properties of Ce(Fe1 xCox)(2) with x = 0 and 0.05 by magnetization measurements under high pressure. In both compound, the remarkable suppression of the magnetization is observed below T* in the ferromagnetic (FM) state under 1.2 GPa. T* shifts to lower temperature with increasing the magnetic field, and the extrapolated value to the zero magnetic field is estimated to be 95 and 123 K. These high pressure and magnetic field effects are probably due to the enhancement and the suppression of the AFM spin fluctuation, respectively. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.04.057

H. Kato, H. Kubota, K. Koyama, T. Miyazaki . Fabrication of SmFe<inf>12</inf>/α-Fe thin films as anisotropic nanocomposite magnet . Journal of Alloys and Compounds408 1368 - 1372 2006年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

A series of nanocomposite thin films, composed of α-Fe and c-axis oriented SmFe12 phases, has been synthesized by rf magnetron sputtering onto heated glass substrates. The volume fraction of α-Fe, VFe, in the obtained films ranges from 5% to 85%. According to the Rietveld analysis of X-ray diffraction patterns, the c-axis of each SmFe 12 grain was estimated to locate within a cone with its symmetry axis being normal to the film plane and with the cone angle of 7°. For samples with VFe < 30%, the demagnetization curves with fields applied normal to the film plane have exhibited a good squareness. In small VFe films, the coercivity Hc increased with increasing VFe, took a maximum for VFe ∼ 25%, and then decreased. In the reference system of randomly aligned SmFe12/α-Fe films, on the other hand, we confirmed that Hc decreased monotonically with increasing VFe. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.04.108

H. Okada, K. Koyama, M. Yamada, T. Goto, Y. Makihara, H. Fujii, K. Watanabe . Magnetic properties of Ce(Fe1-xCox)2 under high pressure . J. Alloys Comp. 408-412 144 - 146 2006年査読

K. Hachitani, H. Amanuma, H. Fukazawa, Y. Kohori, K. Koyama, KI, Kumagai, C. Sekine, I. Shirotani . Appearance of successive phase transition in SmRu4P12 under high magnetic fields probed by 31P nuclear magnetic resonance . J. Phsy. Soc. Jpn75 124712 2006年査読

Y. Adachi, K. Izaki, T. Kitai, H. Yoshida, K. Koyama, H. Morita, H. Onodera, T. Kawae and T. Kaneko . Field-induced transitions in single crystals of TbCu4Ag and GdCu4Ag . J. Phys.: Conf. Ser.51 55 - 58 2006年査読

T. Hori, K. Koyama, H. Shiraishi and K. Watanabe . Magnetic properties of NdxEr1-xMn6Sn6 alloys . J. Phys.: Conf. Ser.51 47 - 50 2006年査読

T. Hori, H. Shiraishi, K. Ohoyama, M. Nishi, K. Koyama and K. Watanabe . Magnetic structure of Y1-xNdxMn6Sn6 alloys . Physica B385-386 320 - 322 2006年査読

H. Nishihara, T. Kanomata, Y. Furutani, T. Igarashi, K. Koyama and T. Goto . NMR properties of half-Heusler CoVSb . Phys. Stat. Sol. (c)3 2779 - 2782 2006年査読

D.X. Li, T. Yamamura, S. Nimori, K. Koyama and Y. Shiokawa . Magnetic properties of rare-earth compounds GdPdIn and TmPdIn . J. Alloys. Comp.418 151 - 154 2006年査読

T. Kanomata, T. Igarashi, H. Nishihara, K. Koyama, K. Watanabe, K.U. Neumann, K.R.Z. Ziebeck . Magnetic properties of weak itinerant electron ferromagnet CoVSb . Mater. Trans.47 496 - 500 2006年査読

J. Prchal, H. Kitazawa, T. Furubayashi, P. Javorsky and K. Koyama . Low-temperature structural study of the TbPd1-xNix series . Physica B378-380 1102 - 1104 2006年査読

D.X. Li, S. Nimori, Y.X. Li, K. Koyama and Y. Shiokawa . Magnetic ordering in ternary germanide Nd2CuGe6 . J. Alloys. Comp.408-412 122 - 126 2006年査読

K. Koyama, S. Miura, H. Okada, T. Shigeoka, S. Fujieda, A. Fujita, K. Fukamichi and K. Watanabe, . Magnetocaloric and structural properties of SmMn2Ge2 . J. Alloys. Comp. 408-412 118 - 121 2006年査読

H. Okada, K. Koyama, and K. Watanabe . Specific heat measurement of the spinel compound CuV2S . the AIP Conference Proceedings850 1317 - 1318 2006年査読

A. Himori, S. Ohishi, K. Koyama, K. Watanabe, and T. Shigeoka . Mulitstep metamagnetism of NdRh2Ge2 single crystal . J. Phys.: Conf. Ser.51 63 - 66 2006年査読

E.A. Tereshina, H. Yoshida, A.V. Andreev, I.S. Tereshina, K. Koyama, and T. Kanomata . Interplay between hydrogenation and pressure effects in magnetism of Lu2Fe17 single crystal . High Pressure Res.26 485 - 488 2006年査読

A.V. Andreev, K. Koyama, N.M. Mushnikov, V. Sechovsky, Y. Shiokawa, I. Satoh, and K. Watanabe . Interplay between effects of external pressure and dilution of the U sublattice in UCoAl-base materials: the U0.94Y0.06CoAl case . High Pressure Res.26 475 - 478 2006年査読

K. Koyama, F. Ishikawa, and K. Watanabe . High field x-ray diffraction studies on magnetic refrigerants . Int. J Appl. Electromagnetics and Mechanics23 153 - 163 2006年査読

K. Watanabe, G. Nishijima, S. Awaji, K. Koyama, K. Takahashi, N. Kobayashi and T. Kiyoshi . Cryocooled superconducting magnets for high magnetic fields at the HFLSM and future collaboration with the TML . J. Phys.: Conf. Ser.51 631 - 634 2006年査読

K. Koyama, S. Miura, H. Okada, and K. Watanabe . Development of an extraction type magnetometer under high pressure and high magnetic fields over 200 kOe in the hybrid magnet . J. Phys.: Conf. Ser.51 569 - 572 2006年査読

K. Takahashi, S. Awaji, Y. Sasaki, K. Koyama and K. Watanabe . Design of an 8 MW water-cooled magnet for a 35 T hybrid magnet at the HFLSM . IEEE Trans. Appl. Supercond.16 977 - 980 2006年査読

T. Ito, M. Ishizuka, T. Tsurudome, H. Ookubo, J. Sakuraba, S. Awaji, G. Nishijima, K. Koyama, K. Takahashi and K. Watanabe . Development of a 10 T cryocooled superconducting magnet with a room temperature bore of 360 mm for a 29 T hybrid magnet . Adv. Cryo. Eng.51 1743 - 1748 2006年査読

高橋弘紀、淡路智、佐々木嘉信、小山佳一、渡辺和雄 . 小型冷凍機冷却34T-8MWハイブリッドマグネットへの発展と磁気科学応用 . 低温工学41 316 - 321 2006年査読

K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, N. Kobayashi, M. Ishizuka, T. Itou, T. Tsurudome and J. Sakuraba . Performance of a cryogen-free 30 T-class hybrid magnet . IEEE trans. Appl. Superc.16 934 - 939 2006年査読

秋屋貴博、加藤宏明、佐川眞人、小山佳一、宮崎照宣 . Nd-Dy-Fe-B系焼結磁石の強磁場中熱処理と保磁力 . J. Magn. Soc. Jpn.30 447 - 454 2006年査読

H. Kato, H. Kubota, K. Koyama and T. Miyazaki . Fabrication of SmFe12/α-Fe thin films as anisotropic nanocomposite magnet . J. Alloys. Comp.408-412 1368 - 1372 2006年査読

V. Provenzano, B. Baumgold, R.D. Shull, A.J. Shapiro, K. Koyama, K. Watanabe, N.K. Singh, K.G. Suresh, A.K. Nigam, S.K. Malik . Structure and magnetocaloric properties of the Fe-doped HoTiGe alloy . J. Appl. Phys.99 08K906 2006年査読

F. Ishikawa, K. Koyama, K. Watanabe, T. Asano, and H. Wada . First-order phase transition at the Curie temperature in MnAs and MnAs0.9Sb0.1 . J. Phys. Soc. Jpn75 84604 2006年査読

H. Yabuta, K. Umeo, T. Takabatake, K. Koyama and K. Watanabe . Temperature- and field-induced first-order ferromagnetic transitions in MnFe(P1-xGex) . J. Phys. Soc. Jpn75 113707 2006年査読

K. Koyama, H. Okada, K. Watanabe, T. Kanomata, R. Kainuma, W. Ito, K. Oikawa, K. Ishida . Observation of large magnetoresistance of magnetic Heusler alloy Ni50Mn36Sn14 in high magnetic fields . Appl. Phys. Lett.89 182510 2006年査読

K. Koyama, T. Kanomata, R. Kainuma, K. Oikawa, K. Ishida and K. Watanabe, . High field X-ray diffraction measurements of novel ferromagnetic shape-memory alloy Ni50Mn36Sn14 . Physica B383 24 - 26 2006年査読

K. Koyama, K. Watanabe, T. Kanomata, R. Kainuma, K. Oikawa, and K. Ishida . Observation of field-induced reverse transformation in ferromagnetic shape memory alloy Ni50Mn36Sn14 . Appl. Phys. Lett.88 132505 2006年査読

V.A. Chernenko, V.A. Lvov, T. Kanomata, T. Kakeshita, K. Koyama and S. Besseghini . Martensitic transformation in Ni-Mn-Ga alloy under high magnetic fields . Mater. Trans.47 635 - 638 2006年査読

K. Koyama, T. Kanomata, T. Watanabe, T. Suzuki, H. Nishihara, and K. Watanabe . X-ray powder diffraction studies of Mn3Ga0.97Al0.03C in magnetic fields . Mater. Trans. 47 492 - 495 2006年査読

K. Yagasaki, S. Notsu, Y. Takaesu, T. Nakama, E. Sakai, K. Koyama, K. Watanabe and A.T. Burkov . X ray diffraction on rare earth-3d Laves phase compound of ErCo2 in magnetic field . Physica B378-380 1089 - 1090 2006年査読

S.V. Demishev, A.V. Semeno, A.A. Pronin, N.E. Sluchanko, N.A. Samarin, H. Ohta, S. Okubo, M. Kimata, K. Koyama, M. Motokawa and A.V. Kuznetsov . Low-temperature study of the quantum critical phenomena in CuGeO3:Fe . J. Magn. Magn. Matter.300 e346 - e349 2006年査読

M. Kimata, H. Ohta, K. Koyama, M. Motokawa, R. Kondo, S. Kagoshima, H. Tanaka, M. Tokumoto, H. Kobayashi, and A. Kobayashi . Fermi surface study of organic conductors using a magneto-optical measurement under high magnetic fields . J. Phys.: Conf. Ser.51 359 - 362 2006年査読

M. Kimata, Y. Oshima, K. Koyama, H. Ohta, M. Motokawa, H. Nishikawa, K. Kikuchi, I. Ikemoto . Detailed fermi surface topology of the quasi-one-dimensional conductor (DMET)2I3 . J. Low Temp. Phys.142 523 - 526 2006年査読

H. Kato, T. Akiya, M. Sagawa, K. Koyama, T. Miyazaki . Field-induced alignment of Nd-rich phase and coercivity in sintered Nd-Fe-B magnets . INTERMAG 2006 - IEEE International Magnetics Conference 914 2006年

Hironari Okada, Keiichi Koyama, Kazuo Watanabe . Specific heat measurement of the spinel compound CuV2S4 . LOW TEMPERATURE PHYSICS, PTS A AND B850 1317 - + 2006年査読

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

We have performed specific heat measurements of a high-quality polycrystalline sample of CuV2S4. Two anomalies associated with charge density wave (CDW) transitions are clearly observed at T-t1 = 92 K and T-t2h = 58 K. The anomalies at T-t1 and T-t2h show lambda-type and spike-shaped behavior, indicating second and first order phase transitions, respectively. The electronic specific heat coefficient gamma and the Debye temperature Theta(D) are estimated to be 36 mJ/moIK(2) and 347 K, respectively. gamma of CuV2S4 is much larger than that of CuTi2S4, whereas CuTi2S4 exhibits a CDW gap at low temperature. This enhancement of gamma is probably attributed not only to the electron-phonon interaction but also to electron-electron interactions.

DOI： 10.1063/1.2355192

A. Himori, S. Ohishi, K. Koyama, K. Watanabe, T. Shigeoka . Multistep metamagnetism of NdRh2Ge2 single crystal . YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS51 63 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

Measurements of high-field magnetization up to 18 T, magnetic susceptibility and specific heat have been performed on a tetragonal NdRh2Ge2 single crystal and polycrystalline sample. From the temperature dependences of magnetic susceptibilities, this compound shows an antiferromagnetic behaviour with Neel temperature of 50 K. Another magnetic transition is observed at 37 K. At low temperatures, a multi-step metamagnetic behaviour is observed along the easy c-axis and a strong magnetic anisotropy is seen. The saturation magnetic moment is estimated to be 2.76 mu(B)/f.u.. There are five magnetic phases below the induced ferromagnetic phase in the H-T magnetic phase diagram. To discuss the magnetic behaviours, the CEF analysis has been made.

DOI： 10.1088/1/1742-6596/51/1/012

T. Hori, K. Koyama, H. Shiraishi, K. Watanabe . Magnetic properties of Nd(x)Erl(1-x)Mn(6)Sn(6) alloys . YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS51 47 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We have conducted low- and high-field magnetization measurements and neutron diffraction experiments on NdxEr1-xMn6Sn6 alloys (0 <= x <= 0.5) with hexagonal MgFe6Ge6 type structure. The alloy with x = 0.1 shows a complex helical antiferromagnetism with the magnetic moments rotating in the c plane below the Curie temperature T-C = 340 K, and a ferrimagnetism below the temperature T-t = 100 K. In the ferrimagnetic state, the magnetic moments mu(Mn) and mu(Nd) are parallel to each other, and antiparallel to mu(Er). The alloy with x = 0.4 shows also a similar ferrimagnetic structure below the Curie temperature T-C = 360 K. It is likely that the each magnetic moments are keep a constant values of mu(Mn) = 2.3 mu(B)/Mn atom, mu(Nd) = 3 mu(B)/Nd atom and mu(Er) = 9 mu(B)/Nd atom at 10 K in the whole composition (0 < x <= 0.5). The ferrimagnetic arrangements for the alloys with 0.2 <= x <= 0.5 are not almost disturbed by magnetic field up to 26 T at 4.2 K.

DOI： 10.1088/1/1742-6596/51/1/008

A. V. Andreev, E. Santava, Y. Homma, K. Koyama, T. Yamamura, Y. Shiokawa . Magnetic anisotropy of U2Co17-xSix single crystals. . Recent Advances in Actinide Science, May, I.; Alvares, R.; Bryan, N., Eds. The Royal Society of Chemistry: Cambridge 758 - 760 2006年査読

A. V. Andreev, K. Koyama, N. V. Mushnikov, V. Sechovsky, Y. Shiokawa, I. Satoh, K. Watanabe . Interplay between effects of external pressure and dilution of the U-sublattice in UCoAl-based materials: the U0.94Y0.06CoAl case . High Pressure Research26 ( 4 ) 475 - 478 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Substitution of Y for U in the itinerant 5f-electron metamagnet, UCoAl, transforms the system to a ferromagnetic state. Application of external hydrostatic pressure above 0.3GPa suppresses the spontaneous ferromagnetism and restores the paramagnetism with field-induced transition to ferromagnetic state. However, the transition becomes of the second order instead of the first-order one in parent UCoAl. © 2006 Taylor &amp
Francis.

DOI： 10.1080/08957950601103973

H. Kato, K. Koyama, T. Miyazaki . Effect of high-magnetic-field annealing on the magnetic properties of Nd-Co-B nanocomposite ribbons . INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference 167 2005年12月

M. Kimata, Y. Oshima, K. Koyama, H. Ohta, M. Motokawa, H. M. Yamamoto, R. Kato . Fermi surface study of β′′-(BEDT-TTF)(TCNQ) by magnetooptical measurements . Synthetic Metals153 ( 1-3 ) 369 - 372 2005年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have performed magnetooptical measurements of β′′-(BEDT-TTF)(TCNQ) using a cavity perturbation technique with a millimeter vector network analyzer (MVNA) and a 14 T superconducting magnet at IMR, Tohoku University. The results of ADMRO and SdH measurements at low temperatures are not consistent with the band calculation result. Therefore, we are interested in Fermi surfaces at low temperatures and have performed magnetooptical measurements of β′′-(BEDT-TTF)(TCNQ). Although the band calculation and ADMRO results suggest the existence of Q1D FS, our results suggest the existence of Q2D FS only. From the results of magnetooptical measurements, we discuss the FS topology of this system at low temperatures. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.synthmet.2005.07.308

JL Her, K Koyama, K Watanabe, Provenzano, V, AQ Fu, AJ Shapiro, RD Shull . High-magnetic field X-ray diffraction studies on Gd-5(Ge2-xFex)Si-2 (x=0.05 and 0.2) . MATERIALS TRANSACTIONS46 ( 9 ) 2011 - 2014 2005年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN INST METALS

We performed the powder X-ray diffraction measurements in magnetic fields up to 5T for Gd-5(Ge1.95Fe0.05)Si-2 and Gd-5(Ge(1.8)Fc(0.2))Si-2-With heating from 8 K, the matrix of Gd-5(Ge1.95Fe0.05)Si-2 clearly shows a structural transition from an orthorhombic to a monoclinic structure at the Curie temperature (Tc = 276 K). On the other hand, the matrix of Gd-5(Ge1.8Fe0.2)Si-2 with the orthorhombic structure in the ferromagnetic state shows two-phases co-existence of the orthorhombic and the monoclinic structures above Tc = 303 K, indicating that a small amount of the matrix participates in the transformation. For both samples, the monoclinic structure is suppressed but the orthorhombic structure is enhanced just above Tc by applying a magnetic field, which closely relates to the magnetization process.

DOI： 10.2320/matertrans.46.2011

M Kimata, K Koyama, H Ohta, Y Oshima, M Motokawa, H Nishikawa, K Kikuchi, Ikemoto, I . Development and applications of magnetooptical measurement system equipped with a rotational resonant cavity in the millimeter-wave region . JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS44 ( 7A ) 4930 - 4934 2005年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

A rotational resonant cavity equipped with a millimeter vector network analyzer (MVNA) and a 14T solenoid type superconducting magnet has been developed. The available frequency range is about 50-100GHz. The temperature can decrease to 1.5 K. The cavity can rotate within the precision of one degree. As an example of the application of the new resonant cavity, we have performed detailed magnetooptical measurements of an organic conductor to estimate the Fermi surface topology. The Fermi surface of the quasi-one-dimensional conductor (DMET)(2)I(3) is discussed.

DOI： 10.1143/JJAP.44.4930

H. Kato, M. Ishizone, K. Koyama, T. Miyazaki . Realization of anisotropic nanocomposite magnet in Nd<inf>2</inf>Fe <inf>14</inf>B/α-Fe thin films . Journal of Magnetism and Magnetic Materials290 1221 - 1225 2005年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

A series of Nd2Fe14B/α-Fe nanocomposite thin films, in which the crystallites of the Nd2Fe14B phase are well-oriented, has been synthesized by RF magnetron sputtering onto heated glass substrates. Magnetization curves exhibited single-phase-like hysteresis loops, suggesting that the two phases are firmly exchange-coupled. By comparing the observed magnetization curves with the micromagnetic calculations, we have estimated the intergrain exchange-coupling constants. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2004.11.407

S Miura, K Koyama, H Okada, T Shigeoka, K Watanabe . High-field X-ray diffraction measurement of SmMn2Ge2 . JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS44 ( 3 ) 1258 - 1259 2005年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

The high-field X-ray diffraction measurement of a re-entrant ferromagnet SmMn2Ge2 with a tetragonal structure was carried out. The unit cell volume contracts by approximately 0.3% in the antiferromagnetic (AFM) state, compared with that of the ferromagnetic (FM) state. In the AFM state, the structural distortion recovers due to a high magnetic field, accompanied by the metamagnetic transition from the AFM state to the forced FM state.

DOI： 10.1143/JJAP.44.1258

S. Okubo, D. Fukuoka, M. Kimata, H. Ohta, Y. Inagaki, T. Kumimoto, K. Koyama, M. Motokawa, Z. Hiroi . Oshikawa-Affleck electron spin resonance behavior observed in one-dimensional antiferromagnet BaCu2(Si1-xGex)2O7 (x=0.65) . J. Phys. Soc. Jpn, Suppl.74 80 - 85 2005年1月査読

T. Tsutaoka, Y. Nakamori, K. Koyama and T. Tokunaga . Magnetic and electrical properties of Gd7Rh3 single crystal . J. Magn. Magn. Mater.293 768 - 773 2005年査読

H. Okada, K. Koyama and K. Watanabe . Transport, magnetic, thermal and structural properties of the spinel compound CuTi2S4 . J. Alloys Comp.403 34 - 37 2005年査読

K. Koyama, T. Kanomata and K. Watanabe . High field X-ray diffraction studies on MnFeP0.5As0.5 . Jpn. J. Appl. Phys., 44 L549 - L551 2005年査読

H. Kato, M. Ishizone, K. Koyama and T. Miyazaki . Realization of anisotropic nanocomposite magnet in Nd2Fe14B/a-Fe thin films . J. Magn. Magn. Mater.290-291 1221 - 1225 2005年査読

J.L. Her, K. Koyama, K. Watanabe, V. Provenzano, A. Fu, A.J. Shapiro, and R.D. Shull . High field X-ray diffraction studies on Gd5(Ge2-xFex)Si2 (x=0.05 and 0.2) . Mater. Trans.46 2011 - 2014 2005年査読

K. Koyama, T. Kanomata, T. Matsukawa and K. Watanabe . Magnetic field effect on structural property of MnFeP0.5As0.5 . Mater. Trans.46 1753 - 1756 2005年査読

T. Kanomata, T. Nozawa, D. Kikuchi, H. Nishihara, K. Koyama and K. Watanabe . Magnetic properties of ferromagnetic shape memory alloys Ni2-xCuxMnGa . Int. J Appl. Electromagnetics and Mechanics21 151 - 157 2005年査読

S. Miura, K. Koyama, H. Okada, T. Shigeoka and K. Watanabe, . High-field X-ray diffraction measurements of SmMn2Ge2 . Jpn. J. Appl. Phys.44 1258 - 1259 2005年査読

M. Yoshida, K. Koyama, A. Ochiai, and M. Motokawa . Cyclotron resonance in rare-earth monopnictides . Phys. Rev. B71 75102 2005年査読

M. Kimata, Y. Oshima, K. Koyama, H. Ohta, M. Motokawa, H.M. Yamamoto, R. Kato . Fermi surface study of β”-(BEDT-TTF)(TCNQ) by magnetooptical measurements . Synthetic Metals153 369 - 372 2005年査読

S.V. Demishev, A.V. Semeno, N.E. Sluchanko, N.A. Samarin, A.A. Pronin, V.V. Glushkov, H. Otha, S. Okubo, M. Kimata, K. Koyama, M. Motokawa, A.V. Kuznetsov . Disorder-driven quantum critical behaviour in CuGeO3 doped with magnetic impurity . Physica B359-361 1315 - 1317 2005年査読

M. Kimata, K. Koyama, H. Ohta, Y. Oshima, M. Motokawa, H. Nishikawa, K. Kikuchi and I. Ikemoto . The development and the applications of the magnetooptical measurement system equipped with a rotational resonant cavity in the millimeter-wave region . Jpn. J. Appl. Phys.44 4930 - 4934 2005年査読

S.V. Demishev, A. Semeno, A. Proin, N. Sluchanko, N. Samarin, H. Ohta, S. Okubo, M. Kimata, K. Koyama, M. Motokawa, . The competition between staggered field and antiferromagnetic interaction in CuGeO3:Fe . Prog. Theor. Phys. suppl.159 387 - 391 2005年査読

H. Ohta, M. Kimata, K. Koyama, Y. Oshima, M. Motokawa, H. Nishikawa, K. Kikuchi, I. Ikemoto . Magneto-optical measurement of organic conductor using rotational cavity system . Int. J. Infrared and Millimeter Wave26 1525 - 1530 2005年査読

T. Sakon, K. Koyama, M. Motokawa, A. Muller, B. Barbara, Y. Ajiro . Detailed ESR measurements for the quantum molecular magnet V15 at ultra-low temperatures . Prog. Theor. Phys. suppl.159 302 - 307 2005年査読

KIMATA M, OHTA H, KOYAMA K, OSHIMA Y, MOTOKAWA M, YAMAMOTO H, KATO R . Development of the High Field Magneto-optical Measurement System with a Rotational Cavity . in High magnetic Fields in Semiconductor Physics, Yong-Jie Wang, Lloyd Engel and N. Bonesteel Eds.World Scientific, Singapore 35 2005年査読

M Kimata, H Ohta, K Koyama, OSHIMA Y, M Motokawa, YAMAMOTO M H, KATO R . Development of the High Field Magneto-optical Measurement System with a Rotational Cavity for the Study of Organic Conductors, in High magnetic Fields in Semiconductor Physics, Yong-Jie Wang, Lloyd Engel and N. Bonesteel Eds. . World Scientific, Singapore, 2005pp355-358. 2005年

Susumu Okubo, Daisuke Fukuoka, Motoi Kimata, Hitoshi Ohta, Yuji Inagaki, Takashi Kumimoto, Keiichi Koyama, Mitsuhiro Motokawa, Zenji Hiroi . Oshikawa-Affleck Electron Spin Resonance Behavior Observed in One-Dimensional Antiferromagnet BaCu2(Si1-xGex)(2)O-7 (x=0.65) . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN74 2005年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Submillimeter and millimeter wave electron spin resonance (ESR) measurements of BaCu2(Si1-xGex)(2)O-7, which is a mixed system of an S=1/2 one-dimensional Heisenberg antiferromagnet with the Dzyaloshinskii-Moriya interaction, have been performed to investigate the limitations of the Oshikawa-Affleck theory for the ESR of an S=1/2 one-dimensional Heisenberg antiferromagnet with a staggered field. The magnetic field dependence of the linewidth and the field induced energy gap will be discussed in connection with the Oshikawa-Affleck theory.

DOI： 10.1143/JPSJ.74.80

S Demishev, A Semeno, A Pronin, N Sluchanko, N Samarin, H Ohta, S Okubo, M Kimata, K Koyama, M Motokawa . The competition between staggered field and antiferromagnetic interactions in CuGeO3 : Fe . PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT159 ( 159 ) 387 - 391 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE

The EPR spectra along different crystallographic axes for single crystals of CuGeO3 containing 1% of Fe impurity have been studied in the frequency range 60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck theory suggests that the temperature dependences of the line width and g-factor are formed as a result of the competition between interchain antiferromagnetic interactions and staggered Zeeman energy. It is found that staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.

DOI： 10.1143/PTPS.159.387

K Irisawa, A Fujita, K Fukamichi, M Yamada, H Mitamura, T Goto, K Koyama . Transition between antiferromagnetic and ferromagnetic states in itinerant-electron La(FexAl1-x)(13) compounds . PHYSICAL REVIEW B70 ( 21 ) 1 - 16 2004年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The transition between the antiferromagnetic (AF) and the ferromagnetic (F) states has been investigated with regard to the magnetovolume effect and the spin-fluctuation characteristics in La(FexAl1-x)(13) compounds. The volume V and amplitude of the local magnetic moment M-loc are different between the AF and F states. In the AF state, the field-induced first-order AF-F transition appears and the transition proceeds with two steps in higher Fe concentration regions. The complex temperature dependence of the AF-F transition field is explained by the contribution from both the magnetic and elastic energies caused by the significant temperature variation of amplitude of M-loc. For the two-step transitions, the spin-floplike transition and the increase in amplitude of M-loc occur at the first- and second-step transitions, respectively. In other words, both the localized moment and the itinerant-electron characteristics are concurrently observed.

DOI： 10.1103/PhysRevB.70.214405

M Kimata, H Ohta, K Koyama, Y Oshima, M Motokawa, HM Yamamoto, R Kato . Development of the high field magneto-optical measurement system with a rotational cavity for the study of organic conductors . INTERNATIONAL JOURNAL OF MODERN PHYSICS B18 ( 27-29 ) 3803 - 3806 2004年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WORLD SCIENTIFIC PUBL CO PTE LTD

We have developed a new magneto-optical measurement system with a rotational cavity. It consists of a millimeter vector network analyzer and a 15T solenoid type superconducting magnet and it can go down to 1.5 K. The rotational cavity can be used in the transmission configuration and the rotation can be performed up to almost 360 degrees in 1 degree precision. We will show the magneto-optical measurement results of, beta ''-(BEDT-TTF)(TCNQ) using our new system. We observe the quasi-two-dimensional periodic orbit resonance (POR) in beta ''-(BEDT-TTF)(TCNQ). The Fermi surfaces of this system will be discussed.

DOI： 10.1142/S0217979204027487

H Okada, K Koyama, S Miura, M Yamada, T Goto, Y Makihara, H Fujii, K Watanabe . Pressure effect on the magnetic properties of Ce(Fe1-xCox)(2) . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN73 ( 7 ) 1982 - 1986 2004年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We have studied the magnetic properties of Ce(Fe1-xCox)(2) with x less than or equal to 0.1 by magnetization measurements under high pressures up to 1.2 GPa. In pure CeFe2, the Curie temperature T-C decreases, and the saturation magnetization M-s is suppressed by applying pressure. In Co substitution compounds, the transition temperature T-A from the ferromagnetic (FM) to the antiferromagnetic (AFM) states and the metamagnetic transition field B-c increase with increasing pressure, while T-C and the magnetization of the spontaneous and field-induced FM states decrease. The obtained results indicate that the AFM state becomes stable by the lattice contraction.

DOI： 10.1143/JPSJ.73.1982

T Hasebe, S Okada, M Ishizuka, T Tsurudome, T Ito, H Ookubo, J Sakuraba, K Watanabe, S Awaji, K Koyama, G Nishijima, K Takahashi . Design of a cryocooler-cooled large bore superconducting magnet for a 30 T hybrid magnet . IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY14 ( 2 ) 368 - 371 2004年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We are now developing a 30 T hybrid magnet utilizing a cryocooler-cooled superconducting magnet wound with highly strengthened (Nb, Ti)(3)Sn. Diameter of the room temperature bore of the superconducting magnet is 360 mm and it generates 11.1 T. Water cooled resistive insert magnet generates 18.9 T, thus the hybrid magnet generates a central field of 30.0 T. The (Nb, Ti)(3)Sn multifilamentary wires are strengthened by Cu/NbTi composite which volume ratio in conductor is about 35%. The reinforcing Cu/NbTi composite changes to CuTi intermetallic compounds during heat treatment for reaction of (Nb, Ti)(3)Sn phase formation. The Nb3Sn coil with inner diameter of 400 mm will be fabricated by wind and react method with Cu/NbTi reinforced (Nb, Ti)(3)Sn wires. The innermost section of Nb3Sn coil is wound with a wire which diameter is 1.85 mm and next second section is wound with a wire diameter of 1.8 mm. The Nb3Sn coil is operated at 303 A and generates 5.8 T. The NbTi coil is wound with NbTi wires of 2.0 mm and 1.6 mm diameters. The NbTi coil generates 5.3 T at an operating current of 350 A. The maximum hoop stress is under 220 MPa for Nb3Sn coil and 200 MPa for NbTi coil.

DOI： 10.1109/TASC.2004.829672

A Fujita, K Fukamichi, K Koyama, K Watanabe . X-ray diffraction study in high magnetic fields of magnetovolume effect in itinerant-electron metamagnetic La(Fe0.88Si0.12)(13) compound . JOURNAL OF APPLIED PHYSICS95 ( 11 ) 6687 - 6689 2004年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

Magnetovolume effect due to the itinerant-electron metamagnetic (IEM) transition in La(Fe0.88Si0.12)(13) has been investigated by x-ray diffraction measurements in high magnetic fields. No crystal structure change was confirmed after the IEM transition. The relative change in the lattice constant measured perpendicular to the magnetic field direction is similar to the longitudinal linear magnetostriction, and hence the volume change due to the IEM transition is isotropic. The volume change in both the ferromagnetic and the paramagnetic states is proportional to the square of the magnetization, though the magnetovolume coupling constant in the former is smaller than that in the latter. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1667455

B Ohta, S Okubo, D Fukuoka, Y Inagaki, T Kunimoto, M Kimata, K Koyama, M Motokawa, Z Hiroi . Breather excitation observed by high-field ESR in one-dimensional antiferromagnet BaCu2(Si1-xGex)(2)O-7 (x=0.65) . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS272 929 - 930 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We have performed the high-field ESR of the one-dimensional BaCu2(Si1-xGex)(2)O-7 (x = 0.65) antiferromagnet at 0.5 and 1.8 Kin the wider frequency and magnetic field region (40-500 GHz, up to 30 T), and found the breather excitation predicted by the Oshikawa-Affleck (OA) theory. The observed field-induced gap for Bparallel toc (chain direction) shows the B-2/3 dependence suggested by the OA theory, and the dependence is weak for the other directions which is consistent with the anisotropy of the Dzyaloshinsky-Moriya interaction. The results will be also discussed in connection with the breather excitation observed in Cu-benzoate. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.547

Keiichi Koyama, Takeshi Kanomata, Tatsuo Watanabe, Takanori Suzuki, Hironori Nishihara, Kazuo Watanabe . Magnetic transitions in Mn3Ga1-xAlxC (0 <= x <= 0.1) . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS272 E615 - E617 2004年5月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We have performed the magnetization and X-ray diffraction measurements on Mn3Ga1-xAlxC (0 <= x <= 0.1) with a perovskite-type structure in the temperature T range from 5 to 400 K to investigate the behavior of the complicated magnetic phase transitions. The obtained results suggest that the crystallographic character is closely correlated to the magnetic properties. The new magnetic phase diagram of this system is presented, which indicates the two-phases coexistence in Mn3Ga1-xAlxC at lower temperature. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.312

M Itoi, A Taira, M Enomoto, N Matsushita, N Kojima, Y Kobayashi, K Asai, K Koyama, T Nakano, Y Uwatoko, J Yamaura . Crystal structure and structural transition caused by charge-transfer phase transition for iron mixed-valence complex (n-C3H7)(4)N[(FeFeIII)-Fe-II(dto)(3)] (dto = C2O2S2) . SOLID STATE COMMUNICATIONS130 ( 6 ) 415 - 420 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

(n-C3H7)(4)N[(FeFeIII)-Fe-II(dto)(3)] shows a new type of first order phase transition called chare-transfer phase transition around 120 K. where the charge transfer between Fe-II and Fe-III occurs reversibly. Recently, we have succeeded in obtaining single crystals of the title complex and determined the crystal Structure at room temperature. Crystal data: space group P6(3), a = 10.0618(5) Angstrom. c = 16.0424(7) Angstrom. V = 1406.54(12)Angstrom, Z = 2. Moreover. we have investigated the structural transition caused by the charge-transfer phase transition by means of powder X-ray diffraction measurement. When the temperature is decreased. the a-axis. which corresponds to the hexagonal ring size in two-dimensional honeycomb network structure of [Fe-II Fe-III(dto)(3)](infinity). contracts by 0.1 Angstrom at the charge-transfer transition temperature (T-CT) while the c-axis. perpendicular to the honeycomb network layer. elongates by 0.1 Angstrom at T-CT. Consequently, when the temperature is decreased, the unit cell volume decreases without noticeable anomaly around T-CT, which is responsible for the quite sniall vibrational contribution to the entropy change. compared with usual spin crossover transition. Thus, the charge-transfer phase transition around 120 K for (n-C3H7)(4)N[Fe-II Fe-III(dto)(3)] is regarded as spin entropy driven phase transition. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2004.02.034

Y Makihara, K Koyama, K Fukushima, K Watanabe, H Fujii . X-ray diffraction study on Ce(Fe1-xCox)(2) in high field at low temperature . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS272 608 - 610 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The temperature and magnetic field dependences of lattice parameter for Ce(Fe1-xCox)(2) with x = 0, 0.05 and 0.10 are examined by powder X-ray diffraction measurement. The strong correlation between structural phase and magnetic state in these compounds is discussed. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.245

K Koyama, K Fukushima, M Yamada, T Goto, Y Makhara, H Fujii, K Watanabe . High-field X-ray diffraction and high-pressure magnetization measurements of the pseudobinary compound Ce(Fe0.9Co0.1)(2) . PHYSICA B-CONDENSED MATTER346 187 - 190 2004年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The magnetic and structural properties of Ce(Fe0.9Co0.1)(2) with the C15 cubic Laves-phase structure have been studied by magnetization measurement in high magnetic fields under high pressures, and powder X-ray diffraction measurement in fields up to 5 T. The C15 cubic structure is distorted to rhombohedral symmetry accompanied with the magnetic phase transition from the ferromagnetic to the antiferromagnetic state, which recovered the C15 structure by applying the magnetic field. The antiferromagnetic phase is induced by the lattice contraction due to hydrostatic pressure. Obtained results suggest that the AFM correlation due to the Cc 4f-Fe 3d hybridization plays an important role on the structural and magnetic properties. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.01.047

Y Oshima, M Kimata, K Kishigi, H Ohta, K Koyama, M Motokawa, H Nishikawa, K Kikuchi, Ikemoto, I . Observation of high-order quasi-one-dimensional periodic orbit resonance in (DMET)(2)I-3 and its Fermi surface . PHYSICA B-CONDENSED MATTER346 387 - 391 2004年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Magneto-optical measurements of a quasi-one-dimensional (q1D) organic superconductor (DMET)(2)I-3 has been performed by using a cavity perturbation technique. Several resonant absorption lines, which can be attributed to the q1D periodic orbit resonance (q1D POR), as well as the quite unusual high-order q1D POR coming from the corrugated Fermi surface (FS) in the interlayer direction were observed. Moreover, other harmonic resonances are also observed when the AC electric field is applied along the c*-axis. We will also show its estimated q1D FS from the data analysis where the estimated FS clearly shows why there is no spin-density-wave or charge-density-wave transition in (DMET)(2)I-3 despite having a q1D FS. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.01.112

M. Kimata, Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H. M. Yamamoto, R. Kato . Magnetooptical measurements of β″-(BEDT-TTF)(TCNQ) . Physica B: Condensed Matter346 382 - 386 2004年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Magnetooptical measurements have been performed on β″-(BEDT-TTF) (TCNQ) using the cavity perturbation techniques. β″-(BEDT-TTF)(TCNQ) has very exotic Fermi surface (FS). Several harmonic resonances were observed at various angles. We consider these resonances as q1D-periodic orbit resonance. The obtained Fermi velocity and the scattering time are 4.4×10 4m/s and 2.1×10-11s, respectively. When the magnetic field was rotated in the b*a-plane, the similar resonances are observed. According to these results, the FS topology of the system at low temperature is discussed. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.01.111

K Koyama, K Fukushima, Y Makihara, H Fujii, K Watanabe . X-ray diffraction study on the pseudobinary compound Ce(Fe0.9Co0.1)(2) in high magnetic fields . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN73 ( 3 ) 676 - 680 2004年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We have studied the magnetic and structural properties of Ce(Fe0.9Co0.1)(2) with the C15 cubic Laves-phase structure by low-temperature x-ray diffraction measurements in magnetic fields up to 5 T, and in the temperature range from 9 to 300 K. The C15 structure is distorted to rhombohedral symmetry at 90 K in zero magnetic field, accompanied with the magnetic phase transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) states with decreasing temperature. In the AFM state, it is observed clearly that the rhombohedral distortion state recovers the C15 structure by applying magnetic field, accompanied with the metamagnetic transition from the AFM to the forced FM states with a hysteresis in the magnetization process.

DOI： 10.1143/JPSJ.73.676

O. Nashima, T. Kanomata, Y. Yamaguchi, S. Abe, T. Harada, T. Suzuki, H. Nishihara, K. Koyama, T. Shishido, K. Watanabe and T. Kaneko . Magnetic and electrical properties of Fe3-xVxSi . J. Alloys and Compounds383 298 - 301 2004年査読

H. Wada, H. Yoshida, T. Goto and K. Koyama . Field-induced magnetic transitions of exchange competing system GdMn2Ge2 . J. Magn. Magn. Matter.272-276 591 - 592 2004年査読

K. Koyama, T. Kanomata, T. Watanabe, T. Suzuki, H. Nishihara, and K. Watanabe . Magnetic transitions in Mn3Ga1-xAlxC (0<x<0.1) . J. Magn. Magn. Matter.272-276 e615 - e617 2004年査読

T. Fujiwara, Y. Uwatoko, H. Fujii, K. Koyama, M. Motokawa, and T. Shigeoka . The correlation between the phase transition and valence change of the Yb ionic state induced upon pressurization in YbMn2Ge2 . J. Magn. Magn. Matter.272-276 599 - 600 2004年査読

X. Fan, T. Mashimo, X. Huang, T. Kagayama, A. Chiba, K. Koyama and M. Motokawa . Magnetic properties of Co-Cu metastable solid solution alloys . Phys. Rev. B69 94432 2004年査読

H. Okada, K. Koyama and K. Watanabe . Two-step structural modulations and Fermi liquid state in spinel compound CuV2S4 . J. Phys. Soc. Jpn.73 3227 - 3230 2004年査読

H. Okada, K. Koyama, S. Miura, M. Yamada, T. Goto, Y. Makihara, H. Fujii, K. Watanabe, . Pressure effect on the magnetic properties of Ce(Fe1-xCox)2 . J. Phys. Soc. Jpn.73 1982 - 1986 2004年査読

A. Fujita, K. Fukamichi, K. Koyama, and K. Watanabe . X-ray diffraction study in high magnetic fields of magnetovolume effect in itinerant-electron metamagnetic La(Fe0.88Si0.12)13 compound . J. Appl. Phys.95 6687 - 6689 2004年査読

M. Kimata, Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto, and R. Kato . Magnetooptical measurement of β’’-(BEDT-TTF)(TCNQ) . Physica B346-347 382 - 386 2004年査読

K. Kobayashi, T. Akiya, H. Kato and K. Koyama . Relation between a specific lattice expansion and magnetic anisotropy in Sm2Fe17Nx (0<x<3) samples of intermediate nitrogen concentration . proceedings for 18th workshop on high performance magnets & their applications, (Annecy, 2004) 521 - 528 2004年査読

K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, M. Motokawa, M. Ishizuka, T. Hasebe, and J. Sakuraba . Advances in the first cryogen-free hybrid magnet . IEEE Trans. Appl. Superc. 14 388 - 392 2004年査読

T. Hasebe, S. Okada, M. Ishizuka, T. Tsurudone. T. Ito, H. Ookubo, J. Sakuraba, K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, and K. Takahashi . Design of a cryocooler-cryocooled large bore superconducting magnet for a 30T hybrid magnet . IEEE Trans. Appl. Superc.14 368 - 371 2004年査読

T. Kurusu, M. Ono, S. Hanai, M. Kyoto, H. Takigami, H. Takano, K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, K. Togano . A cryocooler-cooled 19 T superconducting magnet with 52 mm room temperature bore . IEEE Trans. Appl. Superc.14 393 - 396 2004年査読

K. Watanabe, S. Awaji, G. Nishijima, K. Takahashi, K. Koyama, M. Motokawa, and N. Kobayashi . Magnet technology and materials research at the High-Field Laboratory for Superconducting Materials . Physica B346-347 618 - 622 2004年査読

K. Takahashi, C. Umeki, I. Mogi, K. Koyama, S. Awaji, M. Motokawa, and K. Watababe . Magnetic orientation of paraffin in a magnetic levitation furnace . Physica B346-347 277 - 281 2004年査読

H. Kato, T. Miyazaki, M. Sagawa and K. Koyama . Coercivity enhancements by high-magnetic-field annealing in sintered Nd-Fe-B magnets . Appl. Phys. Lett.84 4230 - 4232 2004年査読

K. Irisawa, A. Fujita, K. Fukamichi, M. Yamada, H. Mitamura, T. Goto and K. Koyama . Transition between antiferromagnetic and ferromagnetic states in itinerant-electron La(FexAl1-x)13 compounds . Phys. Rev. B70 214405 2004年査読

K. Koyama, M. Sakai, T. Kanomata and K. Watanabe . Field-induced martensitic transformation in new ferromagnetic shape memory compound Mn1.07Co0.92Ge . Jpn. J. Appl. Phys.43 8036 - 8039 2004年査読

D. Kikuchi, T. Kanomata, Y. Yamaguchi, H. Nishihara, K. Koyama, and K. Watanabe . Magnetic properties of ferromagnetic shape memory alloys Ni2Mn1-xFexGa . J. Alloys and Compounds383 184 - 188 2004年査読

Y. Makihara, K. Koyama, K. Fukushima, K. Watanabe, and H. Fujii . X-ray diffraction study on Ce(Fe1-xCox)2 in high field at low temperature . J. Magn. Magn. Matter.272-276 608 - 610 2004年査読

K. Koyama, K. Fukushima, Y. Makihara, H. Fujii, and K. Watanabe . X-ray diffraction study on the psudobinary compound Ce(Fe0.9Co0.1)2 in high magnetic fields . J. Phys. Soc. Jpn.73 676 - 680 2004年査読

F. Ishikawa, K. Koyama, K. Watanabe, and H. Wada, . X-ray diffraction study of the structural phase transition in MnAs under high magnetic fields . Physica B346-347 408 - 412 2004年査読

K. Koyama, K. Fukushima, M. Yamada, T. Goto, Y. Makihara, H. Fujii, and K. Watanabe . High field x-ray diffraction and high pressure magnetization measurements of the pseudobinary compound Ce(Fe0.9Co0.1)2 . Physica B346-347 187 - 190 2004年査読

F. Ishikawa, K. Koyama, K. Watanabe, T. Asano, and H. Wada . Structural transformation of MnAs1-xSbx under high magnetic fields . Mater. Trans.45 311 - 314 2004年査読

Y. Oshima, M. Kimata, K. Kishigi, H. Ohta, K. Koyama, M. Motokawa, H. Nishikawa, K. Kikuchi, and I. Ikemoto . Observation of high-order quasi-one-dimensional periodic orbit resonance in (DMET)2I3 and its Fermi surface . Physica B346-347 387 - 391 2004年査読

M. Kimata, H. Ohta, K. Koyama, Y. Oshima, M. Motokawa, H.M. Yamamoto, R. Kato . Development of high field magneto-optical measurement system with a rotational cavity for the study of organic conductors . Int. J. Mod. Phys.18 3803 - 3806 2004年査読

M. Yoshida, K. Koyama, M. Shirakawa, A. Ochiai, K. Watanabe, and M. Motokawa . Cyclotron resonance measurements of the high-quality single crystal GdSb . J. Magn. Magn. Matter.272-276 495 - 496 2004年査読

H. Ohta, O. Okubo, K. Fukuoka, Y. Inagaki, T. Kunimoto, M. Kimata, K. Koyama, M. Motokawa and Z. Hiroi . Breather excitation observed by high-field ESR in one-dimensional antiferromagnet BaCu2(Si1-xGex)2O7 (x = 0.65) . J. Magn. Magn. Matter272-276 929 - 930 2004年査読

K. Koyama, T. Tomimatsu, M. Yoshida, D.X. Li, and M. Motokawa . ESR measurements of GdBi . Physica B346-347 155 - 159 2004年査読

T. Sakon, K. Koyama, M. Motokawa, Y. Ajiro, and B. Barbara, "ESR experiments of molecular magnet V15 at ultra-low temperatures . ESR experiments of molecular magnet V15 at ultra-low temperatures . Physica B346-347 206 - 210 2004年査読

Fumihiro Ishikawa, Keiichi Koyama, Kazuo Watanabe, Tetsuya Asano, Hirofumi Wada . Structural Transformation of MnAs1-xSbx under High Magnetic Fields . Materials Transactions45 ( 2 ) 311 - 314 2004年査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japan Institute of Metals (JIM)

Structural transformation induced by magnetic fields on MnAs and MnAs 0.9Sb0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs 0.9Sb0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at TC for MnAs0.9Sb0.1 is of the first-order.

DOI： 10.2320/matertrans.45.311

H Ohta, M Kimata, K Koyama, Y Oshima, M Motokava, H Nishikawa, K Kikuchi, Ikemoto, I . Millimeter wave magneto-optical measurement of organic conductors using a rotational cavity . CONFERENCE DIGEST OF THE 2004 JOINT 29TH INTERNATIONAL CONFERENCE ON INFRARED AND MILLIMETER WAVES AND 12TH INTERNATIONAL CONFERENCE ON TERAHERTZ ELECTRONICS 379 - 380 2004年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

We have developed a rotational resonant cavity equipped with the millimetre vector network analyser and the 14 T superconducting solenoid magnet. The measurement can be performed down to 1.6 K and the frequency range is about 50100 GHz. As an example of its application, the results of the precise angular dependence measurements of the quasi one dimensional organic conductor (DMET)(2)I-3 are presented.

M Yoshida, K Koyama, M Motokawa . Cyclotron resonance experiments on rare-earth monopnictides . JOURNAL OF PHYSICS-CONDENSED MATTER15 ( 28 ) S2119 - S2122 2003年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

Cyclotron resonance (CR) measurements on high-quality single crystals of rare-earth monopnictides have been performed in the frequency range from 50 to 190 GHz. We have successfully observed CR signals for a strongly correlated electron system, CeSb, as well as other rare-earth monopnictides, LaSb and PrSb. We have also observed Doppler-shifted CR including nonlinear behaviour in the frequency-field diagrams.

DOI： 10.1088/0953-8984/15/28/333

Keiichi Koyama, Makoto Yoshida, Dexin Li, Mitsuhiro Motokawa . Electron Spin Resonance of GdX (X=P, As, Sb and Bi) . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN72 2003年6月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Electron spin resonance (ESR) measurements on single crystals of GdX (X = P, As, Sb and Bi) have been performed in the temperature range from 50 to 1.7 K and in the frequency range from 50 to 109 GHz to obtain microscopic information on the magnetic properties. The results obtained indicate that GdX is an "easy-plane" antiferromagnet with the magnetic moment lying in the (111) plane below the Neel temperature. In addition, ESR affected by hyperfine interaction was observed in GdBi.

T Sakon, K Koyama, M Motokawa, H Nojiri, T Asano, Y Ajiro . Electron spin resonance measurements at ultralow temperatures . PHYSICA B-CONDENSED MATTER329 1629 - 1631 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

An electron spin resonance (ESR) measurement system for use at ultralow temperatures using a He-3-He-4 dilution refrigerator has been developed down to 160 mK. As the first experiment, the ESR was measured on a quantum spin chain Cu benzoate, in which a field-induced gap was recently found. The evaluation of a new ESR mode, so-called breather mode, was found at the lowest temperatures. In the present work, we observed a smaller gap in Hparallel tob by suppressing of the thermal excitation. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02433-X

T. Suzuki, H. Matsui, H. Tsuchiya, E. Negishi, K. Koyama, N. Toyota . Antiferromagnetic resonance in λ-(BEDT-TSF)<inf>2</inf>FeCl <inf>4</inf> . Synthetic Metals135 ( 1-3 ) 567 - 568 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

An antiferromagnetic resonance in λ-(BETS)2FeCl 4 has been observed at 23-110 GHz in the antiferromagnetic insulating state. The frequency-field diagram, which is basically explained by a two-sublattice model, indicates that the spin system has a biaxial anisotropy and the a*-axis is close to the hard axis. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0379-6779(02)00745-2

Y Oshima, H Ohta, K Koyama, M Motokawa, H Nishikawa, K Kikuchi, Ikemoto, I . Magnetooptical measurements of quasi-one-dimensional conductor (DMET)(2)I-3 . SYNTHETIC METALS135 ( 1-3 ) 531 - 532 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

Magnetooptical measurements of quasi-one-dimensional organic conductor (DMET)(2)I-3 have been performed by using a cavity perturbation technique with Millimeter Vector Network Analyzer (MVNA). Several resonances are observed and these resonances disappear when the magnetic field is applied nearby the conducting b-axis. These resonances seem to come from the periodic modulation of group velocities of the carriers on the quasi-one-dimensional Fermi surface (q1D FS). However, these resonances show a different angular dependence with the Fermi traversal resonance (FTR) or quasi-one-dimensional periodic orbit resonance (q1D POR).

DOI： 10.1016/S0379-6779(02)00721-X

H. Ohta, Y. Oshima, Y. Inagaki, S. Okubo, M. Kimata, K. Koyama, M. Motokawa, T. Mori . Magneto-optical measurements of β-(BEDT-TTF)<inf>2</inf>AuI <inf>2</inf> . Synthetic Metals135 ( 1-3 ) 527 - 528 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Magneto-optical measurements of β-(BEDT-TTF)2AuI 2, which has an Isotropic two dimensional Fermi surface in the ab-plane, have been performed at 1.8 K by using cavity perturbation technique with steady magnetic field and mosaic transmission technique with pulsed magnetic field. A cyclotron resonance coming from the quasi two dimensional Fermi surface has been observed in both measurements for H⊥ab-plane. Obtained effective mass was 0.9 mc and this result is smaller than the mass obtained by the Shubnikov-de Haas measurement, which suggests the existence of electron-electron interactions in the system. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0379-6779(02)00718-X

Tsutomu Mashimo, Xinsheng Huang, Xu Fan, Keiichi Koyama, Mitsuhiro Motokawa . Erratum: Slater-Pauling curve of Fe-Cu solid solution alloys (Physical Review B - Condensed Matter and Materials Physics (2002) 66 (132407)) . Physical Review B - Condensed Matter and Materials Physics67 999021 2003年3月

K Koyama, H Sasaki, T Kanomata, K Watanabe, M Motokawa . Magnetization measurements of weak itinerant electron ferromagnet Ni-Pt alloy . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN72 ( 3 ) 767 - 768 2003年3月

T Suzuki, H Matsui, H Tsuchiya, E Negishi, K Koyama, N Toyota . Antiferromagnetic resonance in lambda-(BEDT-TSF)(2)FeCl4 . PHYSICAL REVIEW B67 ( 2 ) 2003年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

From microwave cavity transmission measurements at 23-110 GHz on lambda-(BEDT-TSF)(2)FeCl4, we have observed an antiferromagnetic resonance (AFMR) in the antiferromagnetic insulating state below the metal-to-insulator transition temperature of T-MI=8.3 K. The frequency-field dependence is fundamentally reproduced with a two-sublattice model for a biaxial anisotropy. The easy axis is confirmed to be the direction tilted by 30degrees from c to b(*), and the hard axis is found to be close to a(*). The spin-flop field is identified to be 1.3 T through the frequency-field dependence for the easy axis. The AFMR is interpreted to be caused by spin waves excited on the pi spins, exclusively due to the large pi-pi exchange interaction estimated by theoretical calculations. The exchange field and anisotropy fields for pi spin systems at 1.2 K are evaluated to be H(E)similar to330 T, H(A)(1)similar to1.5x10(-3) T for the intermediate axis and H(A)(2)similar to5.0x10(-3) T for the hard axis, respectively.

DOI： 10.1103/PhysRevB.67.020408

K. Koyama, H. Sasaki, T. Kanomata, K. Watanabe and M. Motokawa . Magnetic properties of weak itinerant ferromagnet Ni-Pt alloy . Physica B319-333 1121 - 1122 2003年査読

H. Wada, H. Yoshida, T. Goto, K. Koyama and K. Watanabe . Novel field-induced magnetic transitions of GdMn2Ge2 . J. Phys. Soc. Jpn72 3197 - 3203 2003年査読

K. Koyama, H. Sasaki, T. Kanomata, K. Watanabe and M. Motokawa . Magnetization measurements of weak itinerant ferromagnet Ni-Pt alloy . J. Phys. Soc. Jpn72 767 - 768 2003年査読

高橋弘紀、梅木千巧、茂木巌、淡路智、小山佳一、本河光博、渡辺和雄 . 磁気浮上状態で溶融凝固したパラフィンの配向効果 . 日本応用磁気学会誌27 1125 - 1129 2003年査読

F. Ishikawa, K. Koyama, K. Watanabe, and H. Wada . Field induced structural transformation in MnAs . Jpn. J. Appl. Phys.42 L918 - L920 2003年査読

T. Tomimatsu, K. Koyama, M. Yoshida, D.X. Li and M. Motokawa . Observation of antiferromagnetic resonance affected by hyperfine interaction in GdBi . Phys. Rev. B67 14406 2003年査読

K. Koyama, M. Yoshida, D.X. Li and M. Motokawa . Electron spin resonance of GdX (X=P, As, Sb and Bi) . J. Phys. Soc. Jpn. Suppl. B.72 145 - 150 2003年査読

T. Sakon, H. Nojiri, K. Koyama, T. Asano, Y. Ajiro and M. Motokawa . ESR measurements at ultra-low temperatures using a dilution refrigerator . J. Phys. Soc. Jpn. Suppl. B72 140 - 144 2003年査読

H. Ohta, Y. Oshima, Y. Inagaki, S. Okubo, M.Kimata, K. Koyama, M. Motokawa and T. Mori . Magneto-optical measurements of β-(BEDT-TTF)2AuI2 . Synthetic Metals135-136 527 - 528 2003年査読

Y. Oshima, M. Kimata, K. Kishigi. H. Ohta, K. Koyama, M. Motokawa, H. Nishikawa, K. Kikuchi and I. Ikemoto . Fermi surface study of quasi-one-dimensional metals using magneto-optical techniques . Phys. Rev. B68 54526 2003年査読

T. Suzuki, H. Matsui, H. Tsuchiya, E. Negishi, K. Koyama, and N. Toyota . Antiferromagnetic resonance in λ-(BEDT-TSF)2FeCl4 . Synthetic Metals135-136 567 - 568 2003年査読

M. Yoshida, K. Koyama and M. Motokawa . Cyclotron resonance experiments in rare-earth monopnictides . J. Phys.: Condenced Matter15 S2119 - S2122 2003年査読

T. Sakon, K. Koyama, M. Motokawa, H. Nojiri, T. Asano, Y. Ajiro . Electron spin resonance measurements at ultralow temperature . Physica B329 1629 - 1631 2003年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . Observation of cyclotron resonance in CeSb . Physica B329-333 557 - 558 2003年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . Doppler-shifted cyclotron resonance with Alfven waves in LaSb . Physica B329-333 1092 - 1093 2003年査読

M. Yoshida, K. Koyama, M. Shirakawa, A. Ochiai, K. Watanabe, and M. Motokawa . Cyclotron resonance and magnetic resonance in GdSb . J. Phys. Soc. Jpn.73 1763 - 1767 2003年査読

Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto, R. Kato, M. Tamura, Y. Nishio and K. Kajita . Fermi surface study of quasi-two dimensional organic conductors by magnetooptical measurements . J. Phys. Soc. Jpn72 143 - 148 2003年査読

Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H. Nishikawa, K. Kikuchi and I. Ikemoto . Magnetooptical measurements of quasi-one-dimensional conductor (DMET)2I3 . Synthetic Metals135-136 531 - 532 2003年査読

Y. Oshima, H. Ohta, H.M. Yamamoto, R. Kato, K. Koyama, and M. Motokawa . Magnetooptical measurements of BEDT-TTF salts containing supramolecular assemblies . Synthetic Metals133-134 453 - 454 2003年査読

M. Yoshida, K. Koyama, P.C. Canfield, C. Cunningham, S. Nimori, K. Watanabe and M. Motokawa . Cyclotron resonance in PrSb . J. Phys. Soc. Jpn.72 705 - 708 2003年査読

T. Suzuki, H. Matsui, H. Tsuchiya, E. Negishi, K. Koyama, and N. Toyota, . Antiferromagnetic resonance in λ-(BEDT-TSF)2FeCl4 . Phys. Rev.B67 020408(R) 2003年査読

N. Toyota, T. Suzuki, H. Matsui, H. Tsuchiya, E. Negishi, K. Koyama . Antiferromagnetic resonance in (formula presented) . Physical Review B - Condensed Matter and Materials Physics67 ( 2 ) 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

From microwave cavity transmission measurements at 23–110 GHz on (formula presented) we have observed an antiferromagnetic resonance (AFMR) in the antiferromagnetic insulating state below the metal-to-insulator transition temperature of (formula presented) The frequency-field dependence is fundamentally reproduced with a two-sublattice model for a biaxial anisotropy. The easy axis is confirmed to be the direction tilted by (formula presented) from c to (formula presented) and the hard axis is found to be close to (formula presented) The spin-flop field is identified to be 1.3 T through the frequency-field dependence for the easy axis. The AFMR is interpreted to be caused by spin waves excited on the (formula presented) spins, exclusively due to the large (formula presented) exchange interaction estimated by theoretical calculations. The exchange field and anisotropy fields for (formula presented) spin systems at 1.2 K are evaluated to be (formula presented) (formula presented) for the intermediate axis and (formula presented) T for the hard axis, respectively. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevB.67.020408

Keiichi Koyama, Makoto Yoshida, Dexin Li, Mitsuhiro Motokawa . Electron spin resonance of GdX (X=P, As, Sb and Bi) . Journal of the Physical Society of Japan72 145 - 150 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Society of Japan

Electron spin resonance (ESR) measurements on single crystals of GdX (X = P, As, Sb and Bi) have been performed in the temperature range from 50 to 1.7 K and in the frequency range from 50 to 109 GHz to obtain microscopic information on the magnetic properties. The results obtained indicate that GdX is an "easy-plane" antiferromagnet with the magnetic moment lying in the (111) plane below the Néel temperature. In addition, ESR affected by hyperfine interaction was observed in GdBi. © 2003 The Physical Society Japan.

DOI： 10.1143/JPSJS.72SB.145

H Fujii, Sasaki, I, K Koyama . Interstitial alloys as hard magnetic materials . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS242 59 - 65 2002年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

For clarifying the role that the interstitial N atoms played on the microscopic scale for basic magnetism in R2Fe17N3, we determined the enhancements of Fe magnetic moments on the crystallographically different atomic sites and crystalline electric field parameter A, upon nitrogenation by neutron diffraction studies of the rhombohedral Y2Fe17 and Y2Fe17N3.1 and high-field magnetization measurements of single crystalline Nd2Fe17 and Nd2Fe17N3, respectively. The results obtained are compared with those estimated by the band structure calculation. For clarifying the coercivity mechanism in Sm2Fe17N3, we also examined the particle (powder) size and surface cleaning effects on the coercive field mu(0)H(e) for the Sm2Fe17N3 single crystal powder. The results indicate that mu(0)H(e) monotonically decreases with increasing the particle size, suggesting that the coercivity mechanism is of a nucleation type. When there are many nucleation sites on the surface of Sm2FeN3 powder before surface cleaning, the value of mu(0)H(e) is relatively small and reveals strong temperature dependence, while mu(0)H(e) is strongly enhanced by surface cleaning, leading to relatively weak temperature dependence. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(01)01189-1

T Sakon, K Koyama, M Motokawa . Electron spin resonance experiments at ultralow temperatures by means of a dilution refrigerator . REVIEW OF SCIENTIFIC INSTRUMENTS73 ( 3 ) 1242 - 1246 2002年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

An electron spin resonance (ESR) apparatus with a high sensitivity vector network analyzer has been developed for use at ultralow temperatures. The microwave frequency can be varied between 45 and 110 GHz. The resonant cavity was installed in a He-3-He-4 dilution refrigerator which provides ultralow temperatures down to 160 mK. In order to avoid the heating of the cavity and the sample by microwaves or heat leaks in the cryostat, attenuators and thermal anchors were placed at the most suitable positions. As the first experiment, the ESR was measured for a quantum spin chain Cu benzoate. The breather mode, which is a new ESR mode caused by a field induced gap, has been clearly observed at the lowest temperatures. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1448901

K. Koyama, T. Goto, T. Kanomata and R. Note . Magnetization measurement of MnSi just above the critical pressure . Physica B312-313 485 - 486 2002年査読

T. Fujiwara, H. Fujii, K. Koyama and M. Motokawa . Novel magnetism on single crystalline YbMn2Ge2 . Physica B312-313 864 - 866 2002年査読

Kanomata, T. Narita, N. Suzuki, K. Sato, T. Harada, N. Oogawara, K. Koyama and M. Motokawa . Electrical properties of the transition metal compound MnRhP . J. Alloys and Compounds334 68 - 71 2002年査読

T. Mashimo, X. Huang, X. Fan, K. Koyama and M. Motokawa . Slater-Pauling curve of Fe-Cu solid solution alloys . Phys. Rev. B66 132407 2002年査読

H. Fujii, I. Sasaki and K. Koyama . Interstitial alloy as hard magnetic materials . J. Magn. Magn. Mater. 242-245 59 - 65 2002年査読

T. Sakon, K. Koyama and M. Motokawa . Electron spin resonance experiments at ultra-low temperature by means of a dilution refrigerator . Rev. Sci. Instrum.73 1242 - 1246 2002年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . Observation of cyclotron resonance on LaBi . Physica B322 306 - 307 2002年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . The observation of cyclotron resonance in LaSb . Physica B312-313 684 - 685 2002年査読

T. Tomimatsu, K. Koyama, M. Yoshida, D.X. Li and M. Motokawa . Magnetic resonance of GdBi . Physica B312-313 682 - 683 2002年査読

K. Koyama,T. Tomimatsu, M. Yoshida, D.X. Li and M. Motokawa . Observation of cyclotron resonance on GdSb . Physica B312-313 680 - 681 2002年査読

K. Koyama, M. Yoshida, T. Tomimatsu, T. Sakon, D.X.. Li, M. Shirakawa, A. Ochiai and M. Motokawa . Observation of cyclotron resonance in rare-earth monopnictides by millimeter microwave region . J. Phys. and Chem. of Solids.63 1227 - 1230 2002年査読

M. Yoshida, K. Koyama, M. Shirakawa, A. Ochiai, K. Watanabe and M. Motokawa . Cyclotron resonance in CeSb . J. Phys. Soc. Jpn.71 2847 - 2850 2002年査読

Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto and R. Kato . Observation on high-order harmonic resonance in magnetooptical measurements of (BEDT-TTF)2Br(DIA) . J. Phys. Soc. Jpn. 71 1031 - 1034 2002年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa,A. Ochiai and M. Motokawa . Determination of cyclotron effective masses on LaSb . J. Phys. Soc. Jpn.71 1752 - 1756 2002年査読

M. Yoshida, K. Koyama, M. Shirakawa, A. Ochiai, K. Watanabe and M. Motokawa . Observation of Doppler-shifted cyclotron resonance in LaSb . Phys. Rev. B66 233107 2002年査読

M. Motokawa, M. Yoshida, K. Koyama . Nonlinear cyclotron resonance of rare-earth semimetals . Conference Digest - 27th International Conference on Infrared and Millimeter Waves, IRMMW 2002 Pl11 - Pl12 2002年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Institute of Electrical and Electronics Engineers Inc.

The cyclotron resonance is the best way to determine the effective masses of conductors and it is interesting to compare them with other effective masses determined by the de Haas oscillations. According to Kohn's theorem, they are not necessarily coincident with each other because an electron-electron correlation in the strongly correlated electron systems contributes to only the case of the de Haas oscillations. This argument has been studied in the case of organic conductors. On the other hand, it has been difficult to observe the cyclotron resonance absorption in rare-earth semimetals due to necessity of high frequency equipment, high magnetic field, very low temperature and high quality specimen. We have succeeded in observing cyclotron resonance in some rare-earth monopnictide compounds RX (R=rare earth atom, X=pnictgen atom) with NaCl type crystal structure and discussed the relationship between two kinds of masses of these materials. As reference materials, nonmagnetic LaSb and PrSb were also studied. In these cases, we have found new nonlinear resonance lines in addition to the normal cyclotron resonance whose resonance frequencies are linear with respect to magnetic field intensity. We ascribe this effect to the Doppler shift caused by coupling of cyclotron motion of carriers with the Alfven wave propagating in the material.

DOI： 10.1109/ICIMW.2002.1076051

Keiichi Koyama, Makoto Yoshida, Takahiro Tomimatsu, Takuo Sakon, Dexin Li, Makoto Shirakawa, Akira Ochiai, Mitsuhiro Motokawa . Observation of cyclotron resonance in rare-earth monopnictides microwave region . Journal of Physics and Chemistry of Solids63 ( 6-8 ) 1227 - 1230 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

The cyclotron effective masses of rare earth monopnictides were determined. These masses were obtained by cyclotron resonance (CR) measurements in the frequency range between 56 GHz and 190 GHz in the temperature range between 50 K and 0.5 K. The experimental results on CR measurements for single crystals of rare earth compounds were presented using a vector network analyzer (AB millimeter) and a resonant cavity. In addition to normal cyclotron resonance, two anomalous absorption lines were observed for the high quality single crystal of LaSb.

DOI： 10.1016/S0022-3697(02)00053-7

T Sakon, H Nojiri, K Koyama, T Asano, Y Ajiro, M Motokawa . Electron spin resonance study of Cu benzoate using a He-3-He-4 dilution refrigerator . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN70 ( 8 ) 2259 - 2262 2001年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

An electron spin resonance (ESR) measurement system for use at ultralow temperatures using a He-3-He-4 dilution refrigerator has been developed. As the first experiment. the ESR was measured on a quantum spin chain Cu benzoate clown to 160 ml. in which a field-induced gap was recently found.((4)) The evaluation of a new ESR mode. the so-called breather mode, was found at the lowest temperatures. In the previous ESR down to 0.5 K, this mode was clearly found for H // c. in which the magnitude of the gap is largest. In the present work. the achievement of low temperatures enabled us to observe a smaller gap in H // b by suppressing the thermal excitation. The magnitude of the field-induced gap evaluated from the nonlinear field dependence of the mode shows good agreement with that determined by previous specific heat measurements.

DOI： 10.1143/JPSJ.70.2259

H. Kato, M. Ishizone, T. Miyazaki, K. Koyama, H. Nojiri, M. Motokawa, T. Ishizaki . High-frequency ferromagnetic resonance in Nd<inf>2</inf>Fe<inf>14</inf>B/α-Fe nanocomposite films . IEEE Transactions on Magnetics37 ( 4 ) 2567 - 2569 2001年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Thin-film magnets, composed of nanophase dispersed Nd2Fe14B and α-Fe have been synthesized by rf magnetron sputtering. With increasing α-Fe volume fraction VFe, the saturation magnetization increased linearly, while the coercivity decreased. Ferromagnetic resonance measurements were made by using a high-frequency and high-field ESR apparatus, which exhibited two absorption peaks. A model calculation of the resonance field was made for a simplified hard/soft two-sublattice system to analyze these results. Estimated values of the exchange-coupling constant are in good agreement with those deduced from micro-magnetic analysis of the magnetization curves.

DOI： 10.1109/20.951237

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio, K. Kajita . Fermi surface study of θ-(BEDT-TTF)<inf>2</inf>I<inf>3</inf> by cyclotron resonance measurements . Synthetic Metals120 ( 1-3 ) 853 - 854 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Cyclotron resonances of quasi-two-dimensional organic conductor θ-(BEDT-TTF)2I3 have been observed by using Millimeter Vector Network Analyzer (MVNA), V- and W-Band Cavity at 0.5K. Two resonances are observed, and the mode coupling in the cavity suggests that the resonances are cyclotron resonances. Obtained effective masses 1.03me and 2.14me are assigned to be α and β orbits, respectively.

DOI： 10.1016/S0379-6779(00)00711-6

K Koyama, H Fujii, T Goto, H Fukuda, Y Janssen . Magnetic phase transitions of Ce2Fe17 under high pressures and high magnetic fields . PHYSICA B294 168 - 171 2001年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Magnetization measurements have been performed on single-phase Ce2Fe17 with a rhombohedral structure under high pressures up to 1.2 GPa and in magnetic fields B up to 17T to clarify the pressure effect on the magnetic phase transitions. At 0.8 GPa, we observed at least seven magnetic phases in the B-T plane. The results obtained indicate that the hybridization between the Fe 3d- and Ce 4f-electron states plays an important role for the magnetic properties of Ce2Fe17. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(00)00634-7

K. Koyama, H. Fujii, T. Goto, H. Fukuda and Y. Janssen, . Magnetic phase transitions of Ce2Fe17 under high pressure and high magnetic fields . Physica B294-295 168 - 171 2001年査読

T. Kanomata, T. Sasaki, T. Hoshi, T. Narita, T. Harada, H. Nishihara, T. Yoshida, R. Note, K. Koyama, H. Nojiri, T. Kaneko and M. Motokawa . Magnetic and electrical properties of Fe2+xV1-xAl . J. Alloys and Compounds317-318 390 - 394 2001年査読

K. Koyama, T. Sakon, H. Nojiri and M. Motokawa . Observation of new ESR mode at ultra low temperatures and CR of RE compounds by VNA . proceedings for 26th IRMMW (Toulouse 2001) 1 - 6 2001年査読

K. Koyama, T. Tomimatsu, M. Yoshida, D.X. Li and M. Motokawa . Cyclotron resonance of GdSb . J. Phys. Soc. Jpn.70 2371 - 2375 2001年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . Cyclotron resonance of LaBi . J. Phys. Soc. Jpn.70 2078 - 2081 2001年査読

T. Sakon, H. Nojiri, K. Koyama, T. Asano, Y. Ajiro and M. Motokawa . Electron spin resonance study of Cu Benzoate using 3He-4He dilution refrigerator . J. Phys. Soc. Jpn.70 2259 - 2262 2001年査読

K. Koyama, M. Yoshida, D.X. Li and M. Motokawa . Magnetic resonance of GdP . J. Phys. Soc. Jpn.70 2774 - 2777 2001年査読

K. Koyama, M. Yoshida, T. Sakon, H. Nojiri, D.X. Li, T. Suzuki and M. Motokawa . ESR and CR measurements of Gd monopnictides . Physica B294-265 156 - 159 2001年査読

M. Yoshida, K. Koyama, H. Hiraga, Y. Endoh and M. Motokawa . High field ESR measurements of CoS2 . Physica B294-295 145 - 148 2001年査読

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio and K. Kajita . High-field magnetooptical measurements of BEDT-TTF salts . Physica B294-295 431 - 434 2001年査読

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio and K. Kajita, . Fermi surface study of θ-(BEDT-TTF)2I3 by cyclotron resonance measurements . Synth. Metals. 120 853 - 854 2001年査読

H. Ohta, Y. Oshima, T. Sakurai, S. Okubo, T. Tanaka, K. Koyama, M. Motokawa, H. Kikuchi, H. Nagasawa, J.P. Boucher . Observation of direct transition in S=1/2 quantum spin system Cu2(C5N12N2)2Cl4 by high field ESR . J. Magn. Magn. Mater. 226-230 439 - 440 2001年査読

H. Kato, M. Ishizone, T. Miyazaki, K. Koyama, H. Nojiri and M. Motokawa . High-frequency ferromagnetic resonance in Nd2Fe14B/α-Fe nanocomposite films . IEEE Trans. Magn.37 2567 - 2569 2001年査読

加藤宏明、石曽根昌彦、宮崎照宣、小山佳一、野尻浩之、本河光博 . 強磁性共鳴によるナノコンポジット磁石の交換結合の評価 . 日本応用磁気学会誌25 675 - 678 2001年査読

Keiichi Koyama, Hironobu Fujii . Nitrogen gas-solid reaction process and basic magnetism of the interstitially modified rare-earth transition-metal nitrides and . Physical Review B - Condensed Matter and Materials Physics61 9475 - 9493 2000年1月

In this paper, we present our recent results of studies of the nitrogen absorption process, magnetization measurements, and neutron powder-diffraction measurements for interstitially modified nitrides (Formula presented) Ce, Nd, and Sm) and (Formula presented) (1) The studies of nitrogen absorption rates in the (Formula presented) under various (Formula presented)-gas pressure up to 6 MPa indicated that the nitrogen absorption into grain interior is promoted by diffusion of nitrogen atoms under low (Formula presented)-gas pressure, while under high (Formula presented)-gas pressure, the nitrogen absorption is promoted by the grain growth of fully nitrogenated phase (Formula presented) rather than the diffusion, making high-pressure nitrogenation effective for synthesizing high-quality nitrides. (2) The high-field magnetization measurements of the (Formula presented) and (Formula presented) single crystals at 4.2 K indicated that interstitial modification of nitrogen atoms gives rise to a strong enhancement of crystalline electric field (CEF) acting on R atoms, leading to almost three times larger CEF-parameter (Formula presented) upon nitrogenation. (3) Neutron powder-diffraction studies of (Formula presented) and (Formula presented) with rhombohedral structure indicated that the N atoms fully occupy at the (Formula presented) site. The introduction of N atoms into (Formula presented) brought such a strong modification in the Fe magnetic moment that the moment of the (Formula presented) atoms being the nearest to the (Formula presented) atoms is the smallest, whereas the (Formula presented) and/or (Formula presented) atoms being relatively farther from the (Formula presented) atoms have the largest moments at 10 K. The results obtained are discussed on the basis of the calculated electronic band structures. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevB.61.9475

K. Koyama, T. Goto, T. Kanomata and R. Note . Observation of an itinerant metamagnetic transition in MnSi under high pressure . Phys. Rev. B62 986 - 991 2000年査読

K. Koyama and H. Fujii . Nitrogen gas-solid process and basic magnetism of the interstitially modified rare-earth 3d transition-metal nitrides R2Fe17N3 (R=Y, Ce, Nd, Sm) and Y2Co17N3 . Phys. Rev. B61 9475 - 9493 2000年査読

K. Koyama, M. Yoshida, H. Nojiri, T. Sakon, M. Motokawa, D.X. Li and T. Suzuki . Magnetic resonance of GdAs . Physica B281-282 456 - 457 2000年査読

K. Koyama, M. Yoshida, T. Sakon, D.X. Li, T. Suzuki and M. Motokawa . Cyclotron resonance of GdAs . J. Phys. Soc. Jpn69 3425 - 3428 2000年査読

M. Yoshida, K. Koyama, T. Sakon, A. Ochiai and M. Motokawa . Cyclotron resonance of LaSb . J. Phys. Soc. Jpn.69 3629 - 3632 2000年査読

K. Koyama, M. Yoshida, H. Nojiri, T. Sakon, D.X. Li, T. Suzuki and M. Motokawa . Antiferromagnetic resonance and magnetic structure of GdAs . J. Phys. Soc. Jpn.69 1521 - 1525 2000年査読

H. Kato, M. Ishizone, T. Miyazaki, K. Koyama, H. Nojiri and M. Motokawa . Fabrication and magnetic properties of nanophase dispersed Nd2Fe14B / α-Fe and Sm2Fe17N3 / α-Fe films with crystallite orientation of hard phases . proceedings for Sixteenth International Workshop on Rare-Earth Magnets (Sendai 2000) 547 - 549 2000年査読

T. Sakon, H. Nojiri, K. Koyama, T. Asano, Y. Ajiro and M. Motokawa . ESR at ultra-low temperatures and observation of new mode in Cu-Benzoate . proceedings for EPR in the 21st century (Kobe 2000) 807 - 812 2000年査読

Sakon Takuo, Nakanishi Yoshiki, Yoshida Makoto, Koyama Keiichi, Takahashi Fumihiko, Nojiri Hiroyuki, Li De Xin, Suzuki Takashi, Motokawa Mitsuhiro . dHvA Effect and Magnetic Resonance of GdAs . JJAP Series: Physics of Strongly Correlated Electron Systems11 135 - 137 1999年12月

UMEO Kazunori, TAKABATAKE Toshiro, PIETRUS Thomas, LOHNEYSEN Hilbert von, OHMOTO Hirohisa, KOYAMA Keiichi, HANE Shogo, GOTO Tsuneaki . Pressure-Induced Quantum Phase Transition in Ce_7Ni_3 . JJAP series11 154 - 156 1999年2月

H. Fujii, K. Koyama, I. Sasaki, S. Mitsudo and M. Motokawa . Giant magnetic anisotropy in Sm2Fe17 induced by nitrogenation . J. Magn. Soc. Jpn.23 465 - 467 1999年1月査読

T. Sakon, Y. Nakanishi, M. Yoshida, K. Koyama, F. Takahashi, H. Nojiri, D. Li, T. Suzuki and M. Motokawa . dHvA effect and magnetic resonance of GdAs . Physics of strongly correlated electron systems, ed. T. Komatsubara, H. Fujii, Y. Onuki and H. Shiba (Japanese Journal of Applied Physics, Tokyo) 135 - 137 1999年1月

K. Koyama, T. Goto, H. Fujii, H. Fukuda and Y. Janssen . Magnetization measurements of Ce2Fe17 under high pressure and high magnetic fields . J. Magn. Soc. Jpn.23 471 - 473 1999年査読

N. Suzuki, T. Kanomata, R. Konno, T. Kaneko, H. Yamauchi, K. Koyama, H. Nojiri, Y. Yamaguchi and M. Motokawa . Magnetic Phase diagram of CrTe1-xSbx (0.0 ?x ?1.0) . J. Alloys and Compounds290 25 - 29 1999年査読

K. Koyama, T. Goto, T. Kanomata and R. Note . Precise magnetization measurements of single-crystalline FeSi under high pressure . J. Phys. Soc. Jpn. 68 1693 - 1698 1999年査読

K. Koyama, H. Fujii, Y. Makihara, T. Kajitani and Morii . Thermal expansion measurements on rhombohedral Y2Fe17 and Y2Fe17N3.1 . J. Magn. Soc. Jpn.23 468 - 470 1999年査読

K. Umeo, T. Takabatake, T. Pietrus, H. B. Lohneysen, H. Ohmoto, K. Koyama, S. Hane and T. Goto . Pressure-induced quantum phase transition in Ce7Ni3 . Physics of strongly correlated electron systems, ed. T. Komatsubara, H. Fujii, Y. Onuki and H. Shiba (Japanese Journal of Applied Physics, Tokyo) 154 - 156 1999年

N. Suzuki, T. Kanomata, R. Konno, T. Kaneko, H. Yamauchi, K. Koyama, H. Nojiri, Y. Yamaguchi, M. Motokawa . Magnetic phase diagram of CrTe<inf>1-x</inf>Sb<inf>x</inf> (0.0≤x≤1.0) . Journal of Alloys and Compounds290 ( 1-2 ) 25 - 29 1999年

記述言語：英語掲載種別：研究論文（学術雑誌）

Measurements of the high field magnetization of CrTe1-xSbx (0.0≤x≤1.0) were carried out at 4.2 K in pulsed magnetic fields up to 300 kOe. The temperature dependence of the magnetization of CrTe1-xSbx was measured in the temperature range from 4.2 K to 800 K. The magnetic phase diagram of CrTe1-xSbx (0.0≤x≤1.0) was determined, which is similar to the typical one for the mixed crystals of the layered antiferromagnetic and ferromagnetic compounds proposed by de Gennes. © 1999 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0925-8388(99)00244-3

小山佳一, 藤井博信, 光藤誠太郎, 本河光博, 香島純, 安藤由和, CANFIELD P.C. . 窒素侵入型化合物Nd_2Fe_<17>N_3単結晶の磁気異方性 . 日本応用磁気学会誌22 ( 4 ) 345 - 348 1998年4月査読

記述言語：日本語出版者・発行元：公益社団法人日本磁気学会

Single crystals of an interstitially modified nitrogen compound, Nd2Fe17N3, were successfully synthesized for the first time by means of the high-pressure N2 gas nitrogenation technique. High-field magnetization curves along the rhombohedral principal axes for the Nd2Fe17 and Nd2Fe17N3 single crystals at 4.2 K indicated strong anisotropic behaviors, which were analyzed on the basis of a single-ion Hamiltonian including the Zeeman energy, exchange energy, and crystalline electric field (CEF) effect. The results indicate that the second-order CEF coefficient A20 reaches up to −1.5 × 103 K/a20 at 4.2K upon nitrogenation, which is about three times as large as that for Nd2Fe17.

DOI： 10.3379/jmsjmag.22.345

その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10463847

T Kamimori, K Koyama, Y Mori, M Asano, K Kinoshita, J Mochimaru, K Konishi, H Tange . Preferential site occupation of M atoms and the Curie temperature in Y2Fe17-xMx (M = Al, Si, Ga) . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS177 ( Pt.2 ) 1119 - 1120 1998年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The Curie temperature, lattice parameters and the Fe-57 Mossbauer spectra were studied on Y2Fe17-xMx, where M = Al(0 less than or equal to x less than or equal to ), Si(0 less than or equal to x less than or equal to 3.5) and Ga(0 less than or equal to x less than or equal to 11). The analysis of Mossbauer spectrum shows the preferential site occupation of M atoms. The preference has little dependence on M. The behavior of the Curie temperature is closely related not to the lattice dimension but to the preferential site occupation of M. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00972-4