1H NMR in spin density wave phase of (TMTSF)2PF6

We have investigated the multi-phase structure in the incommensurate spin density wave (SDW) phase in (TMTSF)2PF6 with 1H NMR measurement. The temperature dependence of spin lattice relaxation rate T1−1 was measured at ambient pressure with varying the magnetic field up to 2.0 T. The divergent peak of T1−1 was observed at the temperature T∗ well below the SDW transition temperature TSDW in each field. The peak height decreases with increasing the magnetic field, suggesting the divergent increase of low frequency fluctuation of local field at T∗. These behaviors indicate that the phase transition with the magnetic fluctuation, which divides the incommensurate SDW phase into two sub-phases, occurs at T∗. With increasing the magnetic field, the peak temperature T∗ increases from 3 K at 0.3 T to 3.7 K at 1.2 T and shows a saturation behavior above 1.2 T. This indicates that the low temperature SDW sub-phase is stabilized more under the magnetic field around 1 T.