Proton NMR Study of the SDW in (TMTTF)2 SCN

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Abstract
Proton NMR measurements (T2*, T2 and T1) have been made on (TMTTF)2SCN at temperatures between 4 and 300 K. Two maxima in the spin lattice-relaxation rate, near 60 K and 110 K, are associated with the rotational motion of the methyl groups. The metal insulator transition, at 160 K, is signaled by only a very weak anomaly in T1. Inhomogeneous line broadening below the spin-density-wave transition, at 8.8±0.1 K, indicates a SDW amplitude of order 10%. A strong asymmetric lambda anomaly is observed in the relaxation rate at the transition. When compared to earlier results on TMTSF analogs, these data imply that the nature of the spin-density-wave ground state is surprisingly little affected by the opening of the gap at 160 K.