研究者詳細 - 小山　佳一

論文 - 小山　佳一

分割表示 496 件中 181 - 200 件目／全件表示 >>

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

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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

Scopus

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

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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

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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

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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

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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

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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

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