Composite perpendicular recording medium consisting of cocrpt with large h_k⊥ and cocr with positive inter-particle interaction

The demagnetizing field near the top surface of a medium for perpendicular recording is compared with that of a medium for longitudinal recording. On the basis of both the result of this comparison and the output dependence on the medium thickness, a perpendicular medium with a large anisotropy field, H_k⊥ or (H_k⊥-4πM_s), of over 10 or 5 kOe, respectively, is needed to obtain large output and high resolution. Exploiting this large anisotropy field, a composite perpendicular medium with a (Co₇₂Cr₂₈)₇₈Pt₂₂ layer over a Cr-rich Co₇₂Cr₂₈ layer was fabricated. By taking advantage of both the large anisotropy in the upper layer and the strong particle interaction in the lower layer, the composite medium with a merged MR head obtained an S/N of 24.0 dB at 200 kFCI and a D₅₀ of 205 kFCI, with a 50-nm magnetic spacing.