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 investigated by using an analytical transmission electron microscope equipped with an energy dispersive X-ray analyzer. Cr in the CoCrTa medium is extremely localized near the magnetic grain boundaries with a maximum Cr concentration of about 25 at%, while the Cr concentration inside the grains is much lower at about 10 at%. The width of the Cr-enriched region is estimated to be about 1 nm. The segregation structure of the CoCrTa medium is represented by a model consisting of a magnetic hexagonal grain made of a Go-rich core with high saturation magnetization M-s covered by a Cr-enriched thin shell with low M-s. The Cr-enrichment 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 concentration of at most 20 at%. The difference in the Cr segregation structure in these two media is related to the difference in the noise characteristics between the GoCrTa and the CoCrPt media.