MICROSTRUCTURAL SEGREGATION IN COCRTA AND COCRPT LONGITUDINAL MAGNETIC RECORDING MEDIA

Microscopic segregation structures of Co-15.2 at% Cr-4.3 at% Ta and Co -13.4 at% Cr-13.0 at% Pt longitudinal magnetic recording media are inv estigated by using an analytical transmission electron microscope equi pped with an energy dispersive X-ray analyzer. Cr in the CoCrTa medium is extremely localized near the magnetic grain boundaries with a maxi mum Cr concentration of about 25 at%, while the Cr concentration insid e the grains is much lower at about 10 at%. The width of the Cr-enrich ed region is estimated to be about 1 nm. The segregation structure of the CoCrTa medium is represented by a model consisting of a magnetic h exagonal grain made of a Go-rich core with high saturation magnetizati on M-s covered by a Cr-enriched thin shell with low M-s. The Cr-enrich ment is also observed in the CoCrPt medium near the grain boundaries, but with a broader Cr-rich width of more than 2 nm and a maximum Cr co ncentration of at most 20 at%. The difference in the Cr segregation st ructure in these two media is related to the difference in the noise c haracteristics between the GoCrTa and the CoCrPt media.