Preliminary study of 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. The advantage theoretically expected for hard/soft-stacked media was confirmed experimentally. The media consist of a magnetically hard CoPtCr-SiO2 layer underneath a soft NiFe-SiO2 layer. The total thickness of the two layers was set to be smaller than the coherent length of magnetization; the thickness of the CoPtCr-SiO2 layer was fixed at 10 nm, and that of NiFe-SiO2 layer varied from 0 to 4 nm. TEM images revealed that NiFe/CoPtCr stacked grains were well isolated by SiO2 at grain boundaries, similarly to the isolation of single CoPtCr-SiO2 media. No change was observed in the slope of the hysteresis loop by stacking the NiFe-SiO2 layer, suggesting there was no significant change in the intergranular coupling of magnetization. The switching field decreased as NiFe-SiO2 thickness increased, but no significant change was observed in ratio of the magnetic anisotropy energy to thermal energy, KuVact/kT. 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.