Microwave Resonance Linewidth in Single Crystals of Cobalt-Substituted Manganese Ferrite

Abstract

Measurements of the microwave resonance linewidth ΔH are reported for small spherical single crystal specimens of nominal composition Co_xMn_1−xFe₂O₄ where, x=0, 0.02, 0.04, 0.08, 0.10. Accurate chemical analyses have been published. ΔH varies rapidly and linearly with x. At 294°K and 16.9 Gcps the gradients of ΔH against x observed are 4.0×10³ and 3.0×10³ oe per cobalt ion for the [100] and [111] directions, respectively. At 9.6 Gcps the corresponding gradients are 2.7×10³ and 2.1×10³. Measurements on disk samples for x=0.08 gave results similar to those for a sphere. At 16.9 Gcps ΔH is plotted against temperature between 150° and 500°K for x=0, 0.04, and 0.08. Above 250°K ΔH varies only slowly with temperature. Below 150°K ΔH increases and becomes anisotropic rapidly; this is associated with anomalies in the field for resonance. The results suggest that magnon‐magnon scattering by the cobalt does not make a significant contribution to ΔH. The behavior observed bears a qualitative resemblance to that of yttrium iron garnet doped with certain rare‐earth ions, but the fast relaxing ion model, successful for some of these, does not fit the present measurements.