Temperature dependence of magnetocrystalline anisotropy constants in the single variant state of L 1₀-type FePt bulk single crystal

The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L 10 -type Fe60 Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9× 107 erg cm-3 at 5 K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5 K determined by the Sucksmith-Thompson method are 7.4 and 0.13× 107 erg cm-3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio ca due to the thermal expansion.