Barkhausen noise in ferromagnetic metallic glass Fe₄₀Ni ₃₈Mo₄B₁₈

The influence of heat treatment on conventional magnetic properties and Barkhausen noise were studied in ferromagnetic amorphous Fe₄₀Ni ₃₈Mo₄B₁₈ during a half magnetization cycle for both amorphous and crystallized states. The coercivity, H_c, was low in the amorphous specimens and maximum as the crystallization starts, and decreased with further annealing. The differential permeability near to the H_c, μ_c, was high in the amorphous specimens and minimum at the onset of crystallization, then increased with annealing. The single peak behavior of the Barkhausen noise (BN) envelope was a common feature in both amorphous and crystallized specimens, and the variation of peak height with heat treatment was similar to that of μ_c. The magnetic anisotropy energy constant, K_u, was lowest when the crystallite started to nucleate in the amorphous specimen, and increased as the crystallite size grows. The difference between ribbon and transverse directions of BN characteristics such as BN energy, peak height of BN envelope, H_p, and corresponding field strength to H_p, respectively, was the lowest at the onset of crystallization, and increased with K_u. A model was proposed to predict the linear relationship between the magnetic anisotropy energy constant detected by torque measurement and the one evaluated by BN measurement.