CONDUCTION-ELECTRON-SPIN RESONANCE IN THE ORGANIC CONDUCTORS (BEDT-TTF)2X (X equals I3, IBr2).

The electron-spin resonance (ESR) spectra were measured for the single crystals of the three highly-conducting BEDT-TTF cation radical salts, alpha - and beta -(BEDT-TTF)//2I//3 and beta -(BEDT-TTF)//2IBr//2, over the range from 5 to 300 K. When the microwave electric field is applied parallel to the quasi-two-dimensional conducting plane of the crystals, a Dysonian line shape characteristic of conduction-electron-spin resonance is observed even at room temperature. From the temperature dependences of ESR linewidth and line shape of the beta -salts, it is shown that the spin-diffusion time T//D is comparable to the spin-relaxation time T//2 below 10 K, while T//D is very much larger than T//2 above 100 K. The spin-diffusion constants estimated from the penetration depth and T//D are 0. 2 cm**2 s** minus **1 for alpha -I//3, 0. 3 cm**2 s** minus **1 for beta -I//3, and 0. 3 cm**2 s** minus **1 for beta -IBr//2 at room temperature. These values are essentially in agreement with the carrier-diffusion constants evaluated independently by the analysis of the reflectance spectra.