EFFECTS OF TA AND PT ADDITION ON MAGNETIC-PROPERTIES IN COCRTAPT PERPENDICULAR MAGNETIC RECORDING MEDIA

With the rapid increase in recording density in recent years, the deve lopment of media with high coercivity and low noise has become an impo rtant issue in perpendicular as well as longitudinal recording. Compar ed with the CoCr binary system, the CoCrTa system is more effective in increasing coercivity. The increase in coercivity is due to not Ta se gregation but to enhanced Cr segregation at column boundaries caused b y Ta addition. When a Ti underlayer with Uniform thickness was used, t here was no improvement in c-axis alignment of the magnetic layers in CoCrTa and CoCrPt films, although the lattice mismatch of Co ternary a lloys with Ti was much reduced compared with that of the CoCr film wit h Ti. This indicates that there may be no direct heteroepitaxial relat ionship between Ti underlayer and CoCr alloys at the Ti-Co alloy inter face. In the case of the CoCrPt film, perpendicular coercivity increas ed linearly as Pt content increased up to 10at%. When Pt content was a bout 13at%. the shape of the M-H loop showed characteristics of domain wall motion reversal, which indicated strong exchange coupling among columns. When Ta content was increased to 4at% in the CoCrPt film, per pendicular coercivity increased and the shape of the M-H loop suggeste d that the domain wall motion reversal behavior was much reduced. This is thought to be associated with Cr segregation at column boundaries by Ta addition.