Quadrupolar Nuclear Relaxation in the III-V Compounds

Abstract

The results of nuclear quadrupolar spin-lattice relaxation time $T_1$ measurements in most of the III-V compounds and germanium are presented and discussed. It is shown that the $T_1\text{'}\mathrm{s}$ may be correlated with the quadrupole interaction for a free atom and appear to be relatively insensitive to different properties of the materials except for the Debye temperature. A theoretical derivation of the transition probabilities for a point charge zincblende lattice is given. This derivation follows Van Kranendonk's treatment for the NaCl lattice. An attempt is made to relate the point-charge model to the III-V compounds with the aid of experimental multiplication factors. A theoretical derivation, which is based on the spin-temperature concept, and an experimental verification of the dependence of the quadrupolar relaxation time on the nuclear spin are given. The spin dependence, $\frac{1}{T_1}\propto f\left(I\right)=\frac{\mathrm{}(2I+3)\mathrm{}}{I^2\mathrm{}(2I-1)\mathrm{}}$, is important in the interpretation of other experimental data. A theoretical derivation is given of a relaxation time that is isotropic as the orientation of the static field is varied with respect to the crystalline axes. This apparently accounts for the absence of an experimental observation of any systematic variations of the relaxation time with crystal orientation in this and other investigations. An experimental investigation of the temperature dependence of quadrupolar relaxation is reported. The observed temperature dependence varifies Van Kranendonk's predictions for a Raman "two-phonon" process. Debye temperatures of several III-V compounds are obtained from the temperature dependence of the relaxation times.