Thin film γ-Fe2O3 recording disk

Abstract

An α‐Fe2O3 thin film was sputtered onto an Al‐Mg substrate, after which it was transformed to γ‐Fe2O3 by reduction and oxidation and a magnetic memory disk was fabricated. The following results were obtained with regard to these processes: (1) The processing temperature must be below 330°C to maintain the initial surface state of the substrate. (2) If an α‐Fe2O3 film is reduced at 300°C for a few hours and oxidized in air, a homogeneous γ‐Fe2O3 film is obtained. (3) Addition of Ti to the film stabilizes the coercive force and broadens the acceptable conditions for reduction. A γ‐Fe2O3 film, to which Ti and Co have been added, has the following magnetic properties: residual magnetic flux density 2.5 kGs, coercive force 700 Oe, rectangular hysteresis ratio 0.8, coercive squareness 0.76, and film thickness 0.1 ‐ 0.2 μm. (4) Coercive force and demagnetization caused by heating and pressure are as stable as those of an ordinary sprayed magnetic memory medium. A γ‐Fe2O3 thin film disk, processed in the above‐described manner, can have a memory density of 104 − 105 bit/mm2.