The effect of elastic anisotropy on the direct spin-lattice relaxation process in cubic crystals

Abstract

A general expression for the transition probability due to the direct electronic spin-lattice relaxation process is derived in the long-wavelength limit, in the case of a paramagnetic centre substituted in an elastically anisotropic cubic crystal. The comparison with the usual expression based on the isotropic Debye model shows that these anisotropic effects can be accounted for by using a set of corrective factors. From a study of the variations of these factors as a function of the elastic constants of the crystal, it is concluded that the overall correction remains less than an order of magnitude for most cubic crystals. However, these anisotropy effects could in some cases modify appreciably the angular variations of the relaxation times predicted on the basis of the Debye model.