研究者詳細 - 小山　佳一

論文 - 小山　佳一

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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 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

Scopus

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

Web of Science

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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

Web of Science

Scopus

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

Scopus

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

Scopus

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