Ferromagnetic Resonance Linewidth in Cobalt-Substituted Ferrites

The resonance linewidth contribution of small concentrations of cobalt ions substituted in ferrites is investigated by computing the magnon scattering due to the variation from ion to ion of the spin-orbit interaction. The effect of the spin-orbit coupling is particularly large in the cobalt ion because it has a degenerate orbital ground state when situated in a trigonally symmetric crystalline field. The resultant linewidth is found to be of the order of 20–30 oe for each percent of cobalt introduced into a normal (noninversed) ferrite or into magnetite. For other ferrites, the effect of the cobalt ions is diminished because the nonequivalence of all octahedral-site ions destroys the trigonal symmetry of the local crystalline field and lifts the orbital groundstate degeneracy. This diminution is calculated as a function of the degree of inversion.