研究者詳細 - 小山　佳一

論文 - 小山　佳一

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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

Scopus

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.

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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

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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.

Web of Science

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

Web of Science

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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

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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

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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

Web of Science

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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

Web of Science

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

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