THE OPTIMIZATION OF COERCIVITY IN GRANULAR RECORDING MATERIAL USING RAPID THERMAL-PROCESSING

Granular cobalt films about 500nm thick and ranging in composition fro m 0.25-0.85 fraction by volume of cobalt have been prepared by co-sput tering cobalt and silicon dioxide from a mosaic target. At a given spu ttering power and pressure the volume fraction (q) of cobalt in the fi lms is determined by the areal fraction of the SiO2 base target covere d by the cobalt mosaic. Transmission electron microscopy indicates tha t the samples are composed of particles of cobalt with diameters in th e range 2.5nm-6.5nm dispersed in the SiO2 matrix. Magnetic properties of samples with q in the range 0.25-0.85 are measured using a vibratin g sample magnetometer. Samples with q below 0.52 are generally superpa ramagnetic in their as-deposited state. Subsequent rapid thermal proce ssing (RTP) is shown to initiate ferromagnetic behaviour with a coerci vity that increases with processing temperature. optical constants of the films, measured by ellipsometry, are found to be in good agreement with Maxwell Garnett theory. Some films exhibit a saturation polar Ke rr rotation that is significantly greater than that of pore cobalt fil ms.