Characterization of coercivity at a recording speed of granular media for thermally assisted recording

As a fundamental study of thermally assisted recording, remanence coercivity at recording speed and the energy barrier for magnetization switching for granular media were evaluated as a function of temperature T. We characterized those for CoPtCr-oxide granular media as a trial examination. Remanence coercivity was measured at measurement time t′ of 1 s (using an electromagnet) and 10−5 s (pulse field); they were defined, respectively, as Hr and HrP for T of 300–473 K. Assuming that the value of t′ at a recording speed is 1 ns and the value of remanence coercivity at the recording speed, Hr(1 ns), was evaluated by fitting Hr and HrP to Sharrock’s equation. Moreover, the values of the energy barrier for magnetization switching, ΔE, were estimated. The value of Hr(1 ns) at T = 573 K, which is a typical temperature for thermally assisted recording, as estimated by extrapolation was about 6.2 kOe for the single medium and 5.5 kOe for the stacked medium. These values were about 1 order of magnitude larger than...