Electron paramagnetic resonance in exchange-coupled systems with unlike spins. II. The intermediate-coupling regime

Abstract

We analyze the transverse dynamic magnetic susceptibility of an isotropic exchange-coupled system with unlike spins in a uniform external field. An approximate theory for the susceptibility is developed which interpolates between results obtained previously in the limits of strong and weak intersystem coupling. The expression for the susceptibility involves both thermodynamic and relaxation parameters, both of which are shown to be related to various spin-spin correlation functions. When the equal-time correlation functions are evaluated by treating the intersystem interactions in the molecular-field approximation, the resulting expression for the susceptibility is equivalent in form to that obtained from Bloch equations derived by Barnes and Zitcova-Wilcox in their analysis of the resonance of magnetic impurities in metallic hosts.