Preliminary study on (CoPtCr/NiFe)-SiO2 hard/soft-stacked perpendicular recording media

Hard/soft-stacked perpendicular recording media were proposed in order to improve recording writability without notable changes in thermal stability and noise performance. A preliminary study on stacked media consisting of a 10-nm magnetically hard CoPtCr-SiO₂ layer underneath a soft NiFe-SiO₂ layer (0-4 nm) was performed. Transmission electron microscope images revealed that NiFe/CoPtCr stacked grains were well isolated by SiO₂ at grain boundaries, similar to the isolation of single layer CoPtCr-SiO₂ media. No change was observed in the slope of the hysteresis loop on stacking the NiFe-SiO₂ layer, suggesting there was no significant change in intergranular magnetic coupling. The switching field decreased by 2 kOe as the NiFe-SiO₂ layer thickness increased from 0 to 3 nm, without a notable reduction in the stabilizing thermal energy barrier. Moreover, the angular dependence of remanence coercivity indicates that magnetization reversal occurs by coherent rotation in (CoPtCr/NiFe)-SiO₂ stacked media as predicted theoretically, and no significant difference in switching mechanism from single layer CoPtCr-SiO₂ media was observed. We successfully demonstrated that the hard/soft-stacked media show a better recording writability with no notable change in signal-to-media-noise ratio or thermal stability.