Re-entrant phenomena of the organic conductor, DCNQI-Cu salts

Partially deuterated molecular conductor, (DMe-DCNQI-da)2Cu (n=2, 3) exhibit successive metal-insulator-metal transitions at ambient pressure. We have investigated the re-entrant phenomena microscopically by the measurements of 1H-NMR relaxation rate, T1−1, and absorption lineshapes. The transitions are detected from the fact that T1−1 in the insulating state is large due to the appearance of Cu2+ local magnetic moments. In the low temperature metallic state, it has been observed that T1−1 does not follow the Korringa relation: T1T=const. The possibility of 1D-spin fluctuations is considered.