Experiments towards realization of a recording medium capable of supporting near theoretical density

A novel technique is reported for the preparation of dispersions of cobalt particles with a narrow distribution of diameters around an estimated mean of 8.5 nm. Particles of this size have blocking temperatures close to 220 °C and, dispersed to reduce mutual interaction, they constitute a near ideal ultrahigh density recording medium. Production of this medium requires a two-stage process: reactive sputtering to develop a precursor film of cobalt nitride followed by rapid thermal processing in vacuum. The precursor film disassociates leaving the required dispersion of cobalt particles. Varying thickness and density in the precursor films and the conditions attending the disassociation provides some control of the medium magnetic properties. Samples with saturation magnetisation (Ms) between 60% and 20% of bulk cobalt exhibit isotropic magnetic properties in-plane with high remanence and coercivities approaching 2 kOe.