Nuclear relaxation of dilute Cd dopants in liquid semiconductingSexTe1−xalloys

Abstract

The nuclear relaxation of very dilute ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ impurities in liquid Se, Te, and Se-Te alloys has been investigated by measuring the time-dependent perturbation of the angular correlation between γ rays emitted during the decay of ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ to ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$. The relaxation is always within the Abragam-Pound motionally narrowed limit and is found to be a function of the density of paramagnetic dangling bonds, with little explicit composition dependence. In pure Se the relaxation rate is proportional to the dangling-bond spin-fluctuation rate. Two possible models for the ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ relaxation are discussed. Relaxation by magnetic interaction with dangling bonds would imply that the Cd is incorporated as part of a small paramagnetic molecule or ion. Quadrupole interaction due to molecular rotation or Cd bond fluctuations could also be responsible for the ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ relaxation. If molecular tumbling is responsible for the fluctuations, the Cd must be bound into molecules smaller than the polymeric chalcogen molecules at lower temperatures. If bond fluctuations are responsible for quadrupole relaxation of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$, the Cd bond-fluctuation rate is determined by the density of dangling bonds on chalcogen atoms.