Chemical-order-dependent magnetic anisotropy and exchange stiffness constant of FePt (001) epitaxial films

Anomalous Hall voltage was measured for FePt L1₀ films having very high magnetic anisotropy. The magnetic anisotropy K₁ and K₂ were determined with high accuracy by analyzing the magnetization curves obtained from the Hall voltage measurement. The saturation magnetization M_s of the samples with different chemical-order parameter (S) exhibits a different temperature dependence, implying that the Curie temperature weakly depends on S. The first-order anisotropy K₁ gradually increases with S, while the second-order anisotropy K₂ remains almost constant of about 5 × 10⁶ erg/cc. The temperature dependence of K₁ is correlated with S, that is, K₁ with a small S is more temperature dependent than that with a large S. These behaviors are quite similar to the temperature dependence of M_s with different S, and can be explained by the conventional model based on thermal spin fluctuations. The domain wall energy σ_w evaluated by the theoretical analysis of the stripe-domain structure tends to increase linearly with S, in a similar manner as that of K₁, whereas the exchange stiffness constant A of about 1 × 10^-6 erg/cm deduced from σ_w and K_u(=K₁ + K₂) hardly depends on S.