NMR IN SPIN-DENSITY-WAVE PHASE OF (TMTSF)2CLO4

The spin-density wave (SDW) phase of quenched (TMTSF)2ClO4 was investi gated by both measurements of narrow band noise and H-1 NMR relaxation rate. In the rapidly quenched phase, the sharp peak of narrow band vo ltage noise associated with the sliding motion of SDW is abruptly broa dened in the narrow temperature range around 1.7 K much lower than the SDW transition temperature (5.7 K) and becomes undetectable at high t emperature. This indicates that the spatial coherence of sliding motio n is decreasing above this temperature. The divergent behavior in NMR relaxation rate is also observed at 1.7 K in the rapidly quenched phas e. These results suggests that another phase transition occurs in the SDW phase. The temperature of this phase boundary decreases proportion ally with the SDW transition temperature controlled by the anion quenc hing rate. The mechanism of this transition is closely related with th at of the SDW transition.