NMR investigation of spin density wave critical fluctuations in (TMTSF)(2)PF6

We report NMR measurements of the spin density wave (SDW) transition critic al fluctuations in (TMTSF)(2)PF6 at 14.9 MHz and 0.98 GHz. This contributio n to 1/T-1 is nearly independent of the magnetic field alignment and the fr equency on both sides of the transition; above the transition at T-N it var ies as \T - T-N\(theta) with theta = -0.75 +/- 0.08. These observations are consistent with dynamical scaling for the 3D Heisenberg model and show tha t the correlation time for the critical fluctuations responsible for T-1 is less than 2 x 10(-10) s for all temperatures studied. Such behavior is ver y different from that observed in the ordered SDW phase, where the dominant coupling is to SDW phasons whose characteristic times cover a very broad r ange.