Ferromagnetic resonance in cobalt doped magnesium and manganese ferrites

Measurements of the change in anisotropy field and ferromagnetic resonance linewidth due to doping magnesium ferrite and manganese ferrite with cobalt are reported. A large effect upon anisotropy and relatively small effect on the linewidth is observed. The behaviour is explained in a broadly satisfactory manner in terms of a ion theory of the anisotropy and the longitudinal relaxation model, assuming a simple form for the ground doublet energy levels of the Co 2+ ion on octahedral sites. Only about one third of the cobalt ions substituted into the magnesium host contribute to the anisotropy energy, whereas all the ions do so in the other host. The relatively weak effect upon the linewidth is interpreted to show that the Co 2+ ion populations relax between the doublet states in approximately=10 -13 s.