The influence of the packing density on the magnetic behaviour of alumite media

The influence of the pore size, the ratio of length to diameter, the microstructure of the initial growth part of the Fe cylinder and the packing density of the Fe needles on the magnetic behaviour of alumite media are reviewed. It is found that the magnetization reversal is controlled by curling rotation, if the applied field lies along the film normal. The Hc is mainly determined by the diameter of the needles, but it slightly decreases with increasing packing density. If the applied field deviates from the film normal, the magnetic behaviour of alumite media is strongly affected by the packing density. For alumite with a low packing density, the magnetization reversal is controlled by a cos-type of incoherent rotation and a demagnetizing field. For high packing densities, the reversal can be considered as the superposition of a cos-type of incoherent rotation with perpendicular anisotropy and in-plane domain-wall motion. The alumite media can exhibit both pe rpendicular as well as longitudinal anisotropy by an appropriately controlled aspect ratio and the morphology of initial growth part of the iron needles.