研究者詳細 - 小山　佳一

論文 - 小山　佳一

分割表示 496 件中 341 - 360 件目／全件表示 >>

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

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