Nuclear Spin-Lattice Relaxation in Pure and Impure Indium. I. Normal State

Transient nuclear spin-lattice relaxation measurements have been made in indium metal and the InCd, InTl, InSn, and InPb dilute alloy systems, using the ${\mathrm{In}}^{115}$ nuclear-quadrupole-resonance (NQR) spectrum. The theory of spin-lattice relaxation in NQR is described for both magnetic and quadrupolar contributions to the relaxation. Precautions were taken to avoid eddy-current heating. A slight dependence of the relaxation rate on NQR transition was observed. Several explanations of this effect were considered, none of which proved satisfactory. In particular, no evidence was found for quadrupolar relaxation. The relaxation rate increased in the alloys at a rate of a few percent/(at.% solute) for all alloy systems studied. No extrema in relaxation rate in the concentration range 0.5-1-at.% solute were found, in contrast to the behavior of the Knight shift as measured by Hewitt and co-workers. The observed increase in relaxation rate in the alloys may be due either to increased enhancement of the contact relaxation, or to an increase in the noncontact contribution to the total relaxation rate.