CoCrPtTa and Co/Pd perpendicular magnetic recording media with amorphous underlayers

The effect of amorphous carbon underlayers on magnetic properties and read-write characteristics of Co₇₃Cr₁₈Pt₈Ta₃ single layer and Co/Pd multilayer perpendicular magnetic recording media were investigated. The increase in H_c and decrease in α, defined as 4π(dM/dH)_H=Hc, were observed by increasing the underlayer thickness for both Co₇₃Cr₁₈Pt₆Ta₃ and Co/Pd media. The media with a low α value, suggesting a decrease in the exchange coupling, exhibited the higher coercivity and the improvement of S/N ratio. In read-write experiments, the improvement of S/N ratio for the Co/Pd media was achieved up to 400 kFRPI or even higher in the recording density by increasing carbon underlayer thickness, while that for the Co₇₃Cr₁₈Pt₆Ta₃ media was obtained up to ca. 250 kFRPI.