Nuclear-spin-relaxation mechanisms of nuclear-ordered bcc solid 3He in the low-field phase.

Abstract

cw-NMR experiments have been performed on nuclear-ordered bcc solid $^{3}\mathrm{He}$ in the low-field phase. We measured the cw-NMR spectrum and its linewidth as a function of external magnetic fields and temperatures for single-crystal samples having various crystal orientations relative to the external field. From the data on the external magnetic field dependence of the linewidth, we found clear evidence of the field region where the three-magnon process is forbidden. We compared our experimental data with the recent theoretical calculation by Ohmi and Tsubota on the lifetime of a uniform spin precession via the three- and four-magnon processes. The agreement is satisfactory. We estimated the size and distribution of the magnetic domains by using an NMR imaging technique. The size of a magnetic domain was found to be comparable to that of a whole crystal. We found some evidence that a crystal in the ordered phase was distorted (on order of ${10}^{\mathrm{\ensuremath{-}}3}$) uniaxially due to magnetostriction. In some crystal samples, we observed a peculiar field dependence of the antiferromagnetic resonance frequency ${\mathrm{\ensuremath{\Omega}}}_{0}$.