Thermal stability and switching field of hard/soft-stacked perpendicular media

The time dependence of remanence coercivity and thermal stability were investigated for hard/soft-stacked media consisting of a magnetically hard granular layer underneath a very thin soft layer with a large saturation magnetization, Ms. The values of remanence coercivity at measurement times t′=103 and 10−5 s (pulse field) were measured, and defined as Hr and HrP. The remanence coercivity on the recording time scale, Hr (1 ns), and the energy barrier, ΔE/kT, were evaluated by fitting Hr and HrP to Sharrock's equation taking into account the power law variation of the energy barrier, n. The value of Hr (1 ns) for a (Co–Pt)–SiO2 (9 nm)/Co–SiO2 (2 nm) stacked medium with an interfacial coupling control layer was about 9 kOe, which was less than half of that of a (Co–Pt)–SiO2 (9 nm) conventional medium (=21.3 kOe). The value of ΔE/kT for the stacked medium was about 111 (n=0.7), and was not significantly different from the conventional medium. Moreover, no significant difference in the rate of decrease of Hr with increasing temperature was observed between media with and without interlayers. These results indicate that the use of a thin soft layer with high Ms was effective at significantly reducing Hr with no notable change in thermal stability.