First-Principles Study for Finite Temperature Magnetrocrystaline Anisotropy of L10-Type Ordered Alloys

Abstract

We conducted the first-principles calculations for the temperature dependence of magnetic anisotropy energy K(T) for L10-type FePt, MnAl, and FeNi by using the coherent potential approximation for spin transverse fluctuation. The temperature dependence of magnetocrystalline anisotropy (MA) for FePt and MnAl almost follows the relation K(T) ∼ M(T)n (2 < n < 3) [M(T) is the magnetization], which has been suggested to be reproduced using the XXZ spin model, i.e., the Heisenberg model including the two-site anisotropy term \( - \sum\nolimits_{\langle ij\rangle }D_{ij} S_{i}^{z}S_{j}^{z}\). However, the temperature dependence of MA for FeNi cannot be fitted by the simple relation K(T) ∼ M(T)n. To analyze these results, we examined MA by using the XXZ spin model including the single-site anisotropy term \( - \sum\nolimits_{i}D_{i} (S_{i}^{z})^{2}\) with the mean field approximation. We confirm that the results from first-principles calculations are well explained by this spin model. We believe that the first-principles result for FeNi is the first case that can be reproduced using the spin model with Di < 0 and Dij > 0.