Nuclear relaxation in tetramethyltetraselenafulvalene salts (TMTSF) 2X, (X = PF6, ClO4)

The nuclear spin-lattice relaxation of methyl-protons in (TMTSF)2 ClO4 is measured versus temperature between 330 and 40 K. The relaxation from the hyperfine coupling to the itinerant electrons is found to be dominant above 200 K. Similar conclusions apply to (TMTSF)2PF6. At 300 K two regimes of relaxation are identified versus magnetic field : (i) a low-field regime (2-25) kOe where 1/T1 is field independent and (ii) a field regime above 25 kOe where fitting the data with a 1-D diffusion law leads to consistent values of hopping rates along a and b directions. By comparison with earlier measurements on TTF-TCNQ and HMTSF-TCNQ it is concluded that the transverse coupling of (TMTSF)2X is intermediate between that of the two-chain conductors.