Anisotropy Of The Spin Density Wave Onset For (Tmtsf)(2)Pf6 In A Magnetic Field

In order to study the spin density wave transition temperature (T-SDW) in (TMTSF)(2)PF6 as a function of magnetic field, we measured the magnetoresistance R-zz in fields up to 19 T. Measurements were performed for three field orientations B parallel to a, b' and c* at ambient pressure and at P = 5 kbar, that is nearly the critical pressure. For B parallel to c* orientation we observed quadratic field dependence of T-SDW in agreement with theory and with previous experiments. For B parallel to b' and B parallel to a orientations we have found no shift in T-SDW within 0.05 K, both at P = 0 and P = 5 kbar. This result is also consistent with theoretical predictions.