Angular Variation of the Magnetic Properties of Partially Aligned γ-Fe2O3 Particles

Abstract

Using a torsion balance magnetometer, measurements have been made on oriented particles of γ-Fe2O3covering a range of packing densities (5%–60%). Microscope examination revealed that the specimens consisted essentially of long chains of particles, parallel to the orientating field, with varying degrees of cross linkages. Measurements were made as a function of the angle between the direction of the orienting field and the direction of the measuring field. The graphs of Hc (the coercivity) versus angle showed a characteristic peak at about 50° while Hr (the remanence coercivity) has its highest value at 90° to the chains and decreases with decreasing angle. Thus, the samples showed their lowest value of Hc and highest value of Hrat 90° to the chains. Torque curves for clockwise and counter-clockwise rotation were obtained as a function of applied field. From these the rotational hysteresis was calculated and gave the maximum anisotropy field at 2500 oe for each specimen. The integral ∫0∝W/Isd(1/H) was evaluated as 1.6 for the 20% specimen.