Direct measurement in the nanosecond regime of the remanent coercivity in perpendicular media

The switching behavior on a nanosecond time scale of a CoCrPt-based perpendicular medium has been studied both experimentally and by simulation. The sample was composed of a granular storage layer with a saturation remanence close to unity and a soft underlayer. The time-dependent remanent coercivity was measured down to 2.3 ns. The results are in good agreement with the extrapolation of the long time data, in accordance with the thermal switching model proposed by Sharrock, with n = 2/3. The dependence of the switching field in the nanosecond regime on the initial remanence was studied. The remanent coercivity of the saturated sample was found to be lower than that of a partially demagnetized sample. This counter-intuitive behavior was confirmed by simulation, which elucidated the role of the local demagnetizing field in the switching process. The simulation also showed that the effect is sensitive to the time scale of the initial demagnetization process.