Anisotropic Ferromagnetic Resonance Linewidth in Ferrites

Abstract

In disordered magnetic materials such as the ferrites, the dominant source of resonance linewidth can be attributed to processes involving only two elementary excitations: the destruction of a magnon with the creation either of another magnon or a phonon. We here consider only the primary magnon-magnon scattering process. We show that the random variation of the spin-orbit coupling parameters of the disordered ions leads to a resonance linewidth comparable to that observed in ferrites. The particular symmetry of the crystalline fields around the octahedrally coordinated sites causes an anisotropy in the linewidth with a minimum in the [100] directions and a maximum in the [111] directions. This anisotropy of linewidth is in general agreement with experimental observations on typical ferrites, as for example, the measurements of Schnitzler, Folen, and Rado on disordered lithium ferrite.