Nuclear relaxation in solids by diffusion to paramagnetic impurities

Abstract

This paper is an extension of the work of Khutsishvili on the relaxation of dipolar nuclei in insulating crystals due to their interaction with paramagnetic impurities. The influence of the barrier radius for spin-spin diffusion on the relaxation time is taken fully into account, and an expression for T 1 is obtained that is valid for all values of this radius. The expression reduces in the appropriate limit to previously given formulae for the “rapid diffusion” case and for the “diffusion limited” case. A discussion is also given of the magnitude of the barrier radius, and it is shown that is determined by the average “static” moment of the impurity. This moment is strongly influenced by temperature and field, particularly at low temperatures, and there is also a corresponding change in the strength of the interaction of the impurity with the nuclei due to purely statistical effects.