Acta Medica Okayama 61 2 2000 Annealing effects on the magnetic and structural properties of single-crystal TDAE-C-60 EN Takashi Kambe Yoshio Nogami Kokichi Oshima Annealing effects on the magnetic and structural properties of single-crystal TDAE-C-60 are investigated. When a crystal is well-annealed at 350 K, ferromagnetic ordering takes place below 16 K, though no magnetic phase transition is shown in as-grown crystal. The saturated magnetization was obtained to be 0.9+/-0.1 mu(B) per C-60. It was first found that the well-annealed crystal shows a structural phase transition around 180 K, probably associated with the orientational ordering of C-60 molecules. On the other hand, the as-grown crystal undergoes no structural phase transition at least down to 30 K while the motion of C-60 molecules is restricted below around 150 K. The possible relation between the low-temperature structure and the magnetic ordering is discussed. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 71 17 2005 Structural differences in two polymorphs of tetra-kis-(dimethylamino)-ethylene-C-60: An x-ray diffraction study EN Motoyasu Fujiwara Takashi Kambe Kokichi Oshima A type of low-temperature structure for ferromagnetic alpha-tetra-kis (dimethylamino) -ethylene (TDAE)-C-60 is proposed on the basis of low-temperature x-ray analysis. We observed that intense superlattice reflections with odd indices successively appeared below T-s = 170 K. The space group symmetry of the low-temperature phase is determined to be P2(1)/n. Two inequivalent C-60 sites exist in the low-temperature phase, which are indispensable to the orbital ordering model Of C-60. The contact configuration for the neighboring C(60)s along the stacking c direction is uniquely determined. The double bond between the hexagons faces the neighboring pentagon. We found that the surrounding TDAE molecules shift along the c axis (similar to 0.07 angstrom) and that these shifts correlate perfectly to the alignment of C-60. This result indicates that the steric effect betwee n C-60 and TDAE molecules plays an important role in the orientational ordering Of C-60, On the other hand, in the alpha' phase, no structural phase transition was observed below 30 K. This indicates that all the C(60)s are crystallographically equivalent. Structural differences separate the magnetic peculiarities of the two polymorphs in TDAE-C-60. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 329-333 2003 X-ray study of modulated structures of beta-CuxV2O5 713 714 EN Nobuaki Nagao Yoshio Nogami Kokichi Oshima Hiroyuki Yamada Yutaka Ueda High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q0 = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5 . For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observed. A three-fold superlattice structure with q1 = (0, 0.333, 0) appears below 210 K. An incommensurate modulated structure with q2 = (0, 0.26 ? 0.29, 0) coexists below 175 K, whose satellite intensity and b* component Qb have temperature and passing-time dependencies between 140 K and 175 K. The competition between q1 and q2 modulations was also observed. It seems that the q2 is deeply related to the physical property change between 140 K and 180 K confirmed by the decrease in the magnetic susceptibility and the increase in the resistivity. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 99 17 2007 Antiferromagnetic ordering driven by the molecular orbital order of C-60 in alpha '-tetra-kis-(dimethylamino)-ethylene-C-60 EN Takashi Kambe Koichi Kajiyoshi Motoyasu Fujiwara Kokichi Oshima We have studied the ground state of a fullerene-based magnet, the alpha'-phase tetra-kis-(dimethylamino)ethylene-C-60 (alpha'-TDAE-C-60), by electron spin resonance and magnetic torque measurements. Below T-N = 7 K, nonparamagnetic field dependent resonances with a finite excitation gap ( 1.7 GHz) are observed along the a axis. Strong enhancement in their intensity as temperature is decreased is inconsistent with excitation from a singlet state, which had been proposed for the alpha'-phase ground state. Below T-N, nonquadratic field dependence of the magnetic torque signal is also observed in contrast to quadratic field dependence in the paramagnetic phase. The angle-dependent torque signals below T-N indicate the existence of an anisotropy of the bulk magnetization. From both experiments, we propose an antiferro-magnetic ground state driven by the cooperative orientational ordering of C-60 in the alpha'-TDAE-C-60. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 68 14 2003 Polymer phase of the tetrakis(dimethylamino)ethylene-C-60 organic ferromagnet EN Slaven Garaj Takashi Kambe László Forró Andrzej Sienkiewicz Motoyasu Fujiwara Kokichi Oshima High-pressure electron spin resonance (ESR) measurements were performed on tetrakis(dimethylamino) ethylene (TDAE)-C-60 single crystals and stability of the polymeric phase was established in the P-T parameter space. At 7 kbar the system undergoes a ferromagnetic to paramagnetic phase transition due to the pressure-induced polymerization. The polymeric phase remains stable after the pressure release. The depolymerization of the pressure-induced phase was observed at a temperature of 520 K, revealing an unexpectedly high thermal stability of the polymer. Below room temperature, the polymeric phase behaves as a simple Curie-type insulator with one unpaired electron spin per chemical formula. The TDAE(+) donor-related unpaired electron spins, formerly ESR silent, become active above a temperature of 320 K, which demonstrates that the magnetic properties are profoundly defined by miniscule reorientation of TDAE molecules. No potential conflict of interest relevant to this article was reported.