Spin–lattice relaxation in the bcc phase of phase-separated He3–He4 solid mixtures

Abstract

The spin–lattice relaxation time in two samples of He3–He4 solid mixtures with initial concentrations of 0.5% He3 in He4 and 0.5% He4 in He3 is measured by the pulsed NMR method. As a result of phase separation, in both cases two-phase crystals form, having the same helium concentration in the concentrated bcc phase. However, in the first sample the bcc phase forms as small inclusions in an hcp matrix, while in the second sample the bcc phase is the matrix. It is established that in the second case the spin–lattice relaxation occurs in the same way as in pure bulk He3, while in the first case one observes anomalous behavior of the spin–lattice relaxation time at low temperatures. Experiments have shown that this anomaly is due not to the possible influence of the small He4 impurity but to the small dimensions of the inclusions of the of the bcc phase. In this case the main contribution to the relaxation is apparently due to defects formed at the boundaries of the bcc inclusions and the hcp matrix.