Temperature Dependence of the Anisotropy Field of L10 FePt near the Curie Temperature

Near the Curie temperature the anisotropy field of magnetically uniaxial L10 FePt is expected to follow the scaling law $(1-T/Tc)^\beta$ where $T$ is the temperature and $T_c$ the Curie temperature. In the literature $\beta$ values between 0.36 and 0.65 have been reported. Based on recording measurements and micromagnetic analysis, we show that only the values of $\beta$ near the low end of the reported range are compatible with the data. We also conclude that thermally activated magnetization reversal at temperatures near $T_c$ cannot be ignored, even at time scales smaller than 1 ns. We demonstrate that thermally activated magnetization reversal at temperatures close to $T_c$ is well described by conventional theory with a frequency factor $f_0$ of the order of $10^{12}$ Hz. It is reasoned that the unusually high value for $f_0$ is a consequence of the temperature-induced reduction of the degree of alignment of the micro-spins within the grains.