Influence of Magnetic Field Annealing on Soft Magnetic Properties for Nanocrystalline Fe39.4–xCo40Nb2.6Si9B9Cux Alloys

The influence of magnetic field annealing and Cu content on saturation magnetostriction λ_s, effective magnetic anisotropy <;K>, and temperature dependence of initial permeability (μ_i-T curves) for nanocrystalline Fe_39.4-xCo₄₀Nb_2.6Si₉B₉Cu_x (x = 0.5, 1, 1.5) alloys was investigated. The λ_s and <;K> of the alloys were both decreased with Cu content increasing. Magnetic field annealing can obviously reduce λ_s, which is due to the rearrangement of random oriented magnetic domain along applied field direction. The increase of <;K> is due to the presence of a coherent induced magnetic anisotropy K_u under magnetic field annealing, which can be explained in terms of the directional atomic pair ordering theory. In addition, the inverse dependence between μ_i and <;K> could be changed in the case of magnetic field annealing. In contrast to nonmagnetic field annealing, magnetic field annealing can enhance the room- and high-temperature initial permeability of nanocrystalline Fe_39.4-xCo₄₀Nb_2.6Si₉B₉Cu_x (x = 0.5, 1, 1.5) alloys; the reason of which was also analyzed.