Effect of Cobalt Oxide in Porous Nickel Ferrites at Very High Frequency

Abstract

Very high frequency measurements of a series of porous, low-loss ferrites $({\mathrm{NiO}}_{\text{(1−x)}}{\mathrm{CoO}}_x{\mathrm{Fe}}_2{\mathrm{O}}_2)$ are described. In many cases, a resonance-type dispersion appears. Comparison of the data with theory indicates that the dispersion results not from domain rotation but from high-frequency wall resonance. Extrapolation of the data for $\text{x\hspace{0.17em}=\hspace{0.17em}0}$ to theoretical density gives results which are consistent with single-crystal measurements suggesting that the loss in porous nickel ferrite occurs in small, relatively perfect regions or grains.