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

Using a torsion balance magnetometer, measurements have been made on oriented particles of $\mathrm{\gamma -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ covering 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 $H_c$ (the coercivity) versus angle showed a characteristic peak at about 50° while $H_r$ (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 $H_c$ and highest value of $H_r$ at 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 ${\int }_0{\mathrm{\propto W/I}}_s\text{d(1/H)}$ was evaluated as 1.6 for the 20% specimen.