Rotational hysteresis measurements on alumite perpendicular media

Rotational hysteresis energy loss measurements have been performed to support the analysis of the magnetization processes of Fe- and Co-alumite perpendicular recording media. Two measurement techniques gave comparable results within error limits. The rotational hysteresis integral is severly lowered by the demagnetizing field. Normalizing the integral with the remanent magnetization instead of the saturation magnetization gives for Fe-alumite values indicating the curling mode, which was also proved by other measurement techniques. The half width value D(1/H)50 is introduced in the rotational loss graph. This value is an estimate for the dispersion of anisotropy axes and in our case it its proportional to the diameter of the Fe-needles. The in-plane loss is very low for the Fe-alumite samples, whereas it is high for the Co-alumite. In the well aligned Fe-alumite, rotation around the easy-axis does not give rise to an energy loss because no anisotropy is present in the rotation plane to cause irreversible magenetization jumps. The crystal anisotropy of fcc-Fe is small compared to the shape anisotropy of the particles. The high in-plane loss measured for Co-alumite is thought to originate from the dispersion of hcp-axes in the Co-needles.