Thermal stability and recording writability of hard/soft stacked perpendicular media

Abstract

Magnetic properties and recording performance were studied for hard/soft stacked media consisting of a magnetically hard CoPtCr–SiO2 layer (10nm thickness) underneath a soft granular layer. Various kinds of soft layers [NiFe(Cr)–SiO2,CoCr–SiO2,…] were used in the present study. Transmission electron microscope images revealed that the grains of the soft layer grew on CoPtCr grains in all kinds of stacked media with SiO2 segregated at the grain boundaries. However, it was revealed that the grain isolation becomes degraded at the film surface when the soft layer was thicker than a critical thickness, and this thickness was about 7nm for (NiFe∕CoPtCr)–SiO2 media. The stacked structure reduced the coercivity, with no significant change in the slope of the magnetization curve. The reduction in dynamic coercivity H0 reached about 2kOe for stacked media with 3nm soft layers, allowing a reduction of the saturation recording current. Furthermore, no significant changes in the signal to media noise ratio SNmR and thermal stability were observed on stacking the soft layer. We demonstrated that hard/soft stacked media with thin soft layers show better recording writability with no notable change in SNmR or thermal stability.