Magnetic Anisotropy and Rotational Hysteresis in Elongated Fine-Particle Magnets

Abstract

Various aspects of the magnetic anisotropy of electrodeposited elongated single‐domain Fe and FeCo alloy particles are examined with a view to better understanding their process of magnetization. The initial increase of coercivity with increase of the angle between alignment direction and measuring field is in qualitative accord with the prediction of the chain‐of‐spheres model with fanning, as previously proposed, and in contrast to coherent rotation models. Analyses of high‐field torque curves and of the fields at which rotational hysteresis vanishes suggest that an anisotropy is present which is a little greater than predicted by the chain‐of‐spheres model but less than that predicted by the Stoner‐Wohlfarth ellipsoid model, for the observed dimensional ratios. Calculations of the rotational hysteresis in single domain‐particles are extended to the chain‐of‐spheres model. A study of the rotational hysteresis enables a relatively sensitive choice between several models of the magnetization process. Comparison of the observed and predicted values for the rotational hysteresis integral, ${\mathrm{\int (W}}_r{\mathrm{/I}}_s\text{)d(1/H),}$ indicates strongly that a nonuniform rotation process, like fanning in a chain‐of‐spheres, is operative in electrodeposited elongated single‐domain particles.