Ferromagnetic Resonance Linewidth in Cobalt-Substituted Ferrites

Abstract

The effect of small concentrations of substitutional ions on the ferromagnetic resonance linewidth of a host ferrite is calculated. The resonance linewidth arises from magnon scattering induced by the variation from ion-to-ion of the spin-orbit interaction. This interaction is uniquely large for cobalt ions because of the orbital degeneracy of the ground state of the ion in a trigonally-symmetric crystalline field. The resultant contribution to the linewidth is found to be isotropic and of the order of 20-30 oersteds for each percent of cobalt in normal (i.e., noninverse) ferrites or in ferrous ferrite. In other ferrites the effect is diminished by the lifting of the ground-state orbital degeneracy at some of the cobalt sites; this diminution is calculated as a function of the degree of inversion.