NUCLEAR MAGNETIC-RELAXATION OF H-1 IN ORGANIC CATION-RADICAL SALT M-MPYNN(-) (X=CLO4, BF4)()X()

The nuclear spill-lattice relaxation time T-1 of H-1 in the organic ca tion radical salt m-MPYNN(+)X(-) (S=ClO4, BF4) has been measured in th e temperature range 1.5 similar to 200K and in the field range 1 simil ar to 70kOe. The experimental results in high fields were well interpr eted in terms of flip-flop relaxation process involving the pairs of f erromagnetic dimers, whose energy scheme consists of lower triplet- an d upper singlet-states with the gap energy of 20K. An appreciable incr ease of the relaxation rate in low fields below about 10kOe was explai ned by the direct relaxation process due to the band-like spread of ea ch Zeeman level.