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

H. J. Richter, G. J. Parker

Published 2017-03-31Version 1

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.