Magnetic relaxation in amorphous Fe₅Co₇₀Si₁₅B₁₀ alloy

The dependence of initial permeability μ_i(T, t) on annealing time and also the magnetic annealing effect on the magnetic anisotropy were investigated at various temperatures for an amorphous Fe₅Co₇₀Si₁₅B₁₀ alloy. The reversible decrease of μ_i(T, t) after demagnetization (disaccomodation) disappears at about 150°C, while the irreversible decrease of μ_i(T, t) increases in the temperature range from 100 to 250°C. The irreversible decrease of μ_i(T, t) is discussed in connection with the induced magnetic anisotropy constant K_ui(T, t). In this temperature range the relation Δμ_i ≡ {μ_i(T, 0)-μ_i(T, t)} μ_i(T, 0) = K_ui (T,t) {K_ui(T, t) + K′(T)} is obtained, where K′(T) is a magnetic anisotropy constant independent of the annealing time. The annealing temperature dependence of induced magnetic anisotropy is explained by the compositional short-range ordering.