Effect of correlated self-diffusion on the low-field nuclear-spin relaxation in the rotating reference frame

Abstract

The Slichter-Ailion (SA) theory for low-field rotating-frame relaxation by atomic diffusion in crystals is applied to a monovacancy mechanism of self-diffusion under the condition that a spin temperature is established between successive jumps of a nucleus but not between successive jumps of a vacancy (so-called high-temperature region). By means of a computer simulation of the random migration of a vacancy both the existence of a "trail of hot spins" left behind the vacancy and the correlated jumps of neighboring nuclei are taken into account. As special cases the theory includes low-temperature relaxation, where a spin temperature is established even between two successive vacancy jumps, and uncorrelated random-walk diffusion. The extrapolation to high relaxation fields shows the identity of the high-field case as predicted from the SA theory with the results obtained from a perturbation-theory treatment of relaxation due to vacancy-induced self-diffusion by the present author. From the numerical results for the fcc and bcc lattices considerable variations of the orientation dependence of the rotating-frame spin-lattice relaxation time are predicted for both the transition from low temperatures to high temperatures and for the transition from the low-field to the high-field region.