Variation with Temperature of the Magnetocrystalline Anisotropy of Several Nickel Iron Ferrites

Abstract

An investigation of the magnetocrystalline anisotropy K1 by microwave resonance measurements is reported for a series of nickel iron ferrite crystals in the temperature range of 4.2° to 300°K. Values of K1/Ms, where Ms is the saturation magnetization, calculated from previous torque measurements of K1 on similar materials agree with the present measurements of K1/Ms over a temperature range from 300°K to some lower temperature that is dependent on the composition. At this temperature, which decreases with increasing Fe2+ content, the microwave values of K1/Ms decrease sharply, while those derived from torque measurements continue to increase with decreasing temperature. The linewidth ΔH is anisotropic and temperature dependent with ΔH in the [111] direction exhibiting a maximum as a function of temperature. The value of g-effective increases as the temperature is lowered. There is qualitative, although not quantitative agreement between our data and theoretical results due to Clogston. Large magnetic annealing effects occur for each sample below a certain temperature. This temperature also depends upon the Fe2+ content.