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

Abstract

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, M s. The values of remanence coercivity at measurement times t′=10 3 and 10 −5 s (pulse field) were measured, and defined as H r and H r P. The remanence coercivity on the recording time scale, H r (1 ns), and the energy barrier, Δ E/ kT, were evaluated by fitting H r and H r P to Sharrock's equation taking into account the power law variation of the energy barrier, n. The value of H r (1 ns) for a (Co–Pt)–SiO 2 (9 nm)/Co–SiO 2 (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)–SiO 2 (9 nm) conventional medium (=21.3 kOe). The value of Δ E/ 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 H r with increasing temperature was observed between media with and without interlayers. These results indicate that the use of a thin soft layer with high M s was effective at significantly reducing H r with no notable change in thermal stability.