BA-FERRITE THIN-FILM MEDIA FOR HIGH-DENSITY LONGITUDINAL RECORDING

Ba-ferrite is an attractive candidate for future high-density recording media because of its large coercivity, corrosion resistance, high hardness, and durability. In contrast to most recent work on Ba-ferrite thin film media, polycrystalline films with large in-plane remanence for longitudinal recording are emphasized. Films are prepared on a variety of substrates by on-axis sputtering at low temperatures from stoichiometric targets followed by a postdeposition anneal in a rapid thermal processor at approximately 850-degrees-C to induce crystallization. Structural and chemical properties have been investigated by force microscopy, Rutherford backscattering, and other means. Stoichiometric films have large 5000 angstrom grains that are unsuitable for high-density recording. However, grain sizes as small as 200 angstrom have been produced by doping with small amounts of Cr2O3 and other additives. Compositional changes also influence crystallite orientation. Exceptional durability has been observed on disks without overcoats, presumably due to a fine-scale texturing that occurs during crystallization. Coercivities are greater than 4000 Oe even in small grain films. The effect of grain size on coercivity and signal-to-noise ratio of several Ba-ferrite disks is discussed. It is argued that the grains are magnetically decoupled based on the magnetic properties of these films.