高橋 利宏

We have carried out a series of measurements of angular dependence of solid-state NMR spectrum using single crystal samples on various organic molecular conductors, in order to investigate the natures of the electronic states at low temperatures. We confirmed a charge ordered insulating state in alpha-(BEDT-TTF)(2)I-3 and large charge disproportionation in the metallic state of this salt. In another charge ordered system, theta-(BEDT-TTF)(2)RbZn(SCN)(4), we observed unusual NMR line broadening, proportional to resonance shift, in the metallic state above the transition. We found that this broadening is due to charge disproportionation, or more correctly, due to the inhomogeneity of local susceptibility at nuclear sites and analyzed its dynamics. We observed similar broadening in various organic molecular conductors as well, such as theta-(BEDT-TTF)(2)CsZn(SCN)(4), an exotic Bechgaad salt, (TMTSF)(2)FSO3, and lambda-type BETS salts, lambda-(BETS)(2)(Fe,Ga)Cl-4. We found the mechanism of CD in each system is different, respectively. (c) 2012 Elsevier B.V. All rights reserved.

LiNbO3-type MnMO3 (M = Ti, Sn) were synthesized under high pressure and temperature; their structures and magnetic, dielectric, and thermal properties were investigated; and their relationships were discussed. Optical second harmonic generation and synchrotron powder X-ray diffraction measurements revealed that both of the compounds possess a polar LiNbO3-type structure at room temperature. Weak ferromagnetism due to canted antiferromagnetic interaction was observed at 25 and 50 K for MnTiO3 and MnSnO3, respectively. Anomalies in the dielectric permittivity were observed at the weak ferromagnetic transition temperature for both the compounds, indicating the correlation between magnetic and dielectric properties. These results indicate that LiNbO3-type compounds with magnetic cations are new candidates for multiferroic materials.

An A-site ordered perovskite oxide SrCu3Ti4O12 was synthesized under high pressure and temperature conditions. The sample was characterized by the synchrotron X-ray diffraction, dielectric and magnetic susceptibility measurements. The synchrotron X-ray Rietveld refinement revealed that the strontium ion fully occupied on the A-site, while the copper ion at the A'-site was slightly deficient. The dielectric constant was about 160 at 1 kHz at room temperature. The anti-ferromagnetic (AFM) order with a Neel-temperature T-N of at 24.5 K was observed. The ionic radii of the A-site ion had little influence on AFM indirect exchange interaction between Cu2+ ions in A Cu3Ti4O12.