Effect of the gap due to anion ordering in deuterated (TMTSF)2ClO4 at high magnetic fields

Magnetoresistance measurements along the highly conducting a-axis have been carried out in deuterated (TMTSF-d12)2ClO4 for various cooling rates through the anion ordering transition. Magnetic field up to 28 T was applied parallel to the c∗ direction. For a slow cooling, the field-induced spin-density-wave (FISDW) transition temperature, almost independent of field above 15 T in hydrogenated (TMTSF-h12)2ClO4, slightly decreases with increasing field above 20 T in deuterated ones and the phase boundary at 27 T in hydrogenated samples appears at higher field in deuterated ones. The increase of the cooling rate shifts this phase boundary towards a lower field while the FISDW transition temperature increases with increasing field. The cooling rate dependence of the FISDW transition and the phase boundary at high magnetic fields in the (TMTSF-d12)2ClO4 salts can be explained by the decrease of the dimerized gap due to anion ordering.