Ferrite thin films for high recording density

Ferrite thin films were prepared in serial process of vacuum evaporation of iron on an alumina substrate, oxidation of iron surface by alkali treatment, conversion to hematite at a high-temperature in air and reduction to ferrite at a low-temperature in hydrogen atmosphere. In the conversion to the hematite above 900°C, the solution of the alumina to the hematite was taken place to give rise to the firm adhesion of the film to the substrate. Magnetic properties of the ferrite thin films hardly depended on the film thickness in the range of 0.6 μm to 1.5 μm. Hc was 400-500 Oe and Br was 3000-2300 G, depending on the temperature of the annealing in air. In recording characteristics, these films considerably exceeded the conventional γ-Fe2O3coating medium.