Ferrimagnetic Resonance Anomalies in Cobalt-Substituted Manganese Ferrite Crystals

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Abstract
Microwave resonance measurements are reported near 16.8 Gc in the temperature range 1.5° to 77°K for a crystal of composition Co0.005Mn0.995Fe1.99O4. Sharp peaks were observed in the field for resonance and linewidth as a function of orientation below 10°K. The applied field directions for which these peaks occur lie on cones with axes along [111] directions and semivertical angle 34°. At higher temperatures the peaks in ΔH split into two and this splitting increases with increasing temperature. The general resemblance of the behavior below 10°K to that of YIG doped with certain rare‐earth ions is pointed out and by analogy, the peaks are attributed to near crossovers in the low lying energy levels of the cobalt ion. A model for relaxation which was useful for nickel ferrite containing Fe2+ ions and for rare‐earth doped YIG is applied qualitatively and on this basis the minimum energy level splitting at the near crossover is tentatively de‐deduced to be 11 cm−1. The occurrence of crossovers at the angles concerned is not predicted by models for the Co2+ ion which have been used previously in theories of the magnetocrystalline anisotropy of spinel ferrites containing cobalt.