研究者詳細 - 小山　佳一

論文 - 小山　佳一

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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

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

Scopus

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

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

Web of Science

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

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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

Web of Science

Scopus

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

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Scopus

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

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Scopus

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

Web of Science

Scopus

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

Web of Science

Scopus

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

Web of Science

Scopus

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

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論文 - 小山 佳一

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論文 - 小山　佳一