Magnetic anisotropy of amorphous alloy ribbons

Two types of magnetic anisotropy have been identified in amorphous alloy ribbons, prepared by melt spinning. By investigating the effect of annealing treatment on the magnetic torque curves and the dependence of Ku on temperature for Fe-based, FeNi-based and Co-based amorphous alloy ribbons, it was found that the in-plane anisotropy consists of two parts: One is stress anisotropy, Kuσ, associated with the coupling between magnetostriction and internal stress. This internal stress is a macroscopic internal stress, rather than the local stress. Kuσ will affect the magnetisation process directly, but it can be eliminated by stress relief annealing. The other is surface shape anisotropy, Kus, which is much bigger than Kuσ. By comparing Kus with the magnitude of the field-induced anisotropy, Kin, it is found that the surface-shape anisotropy, Kus, determined from the variation of the torque with θ, does not directly influence the magnetisation process. This means that Kus cannot be used as a variable to estimate the magnetisation process. It may reflect the surface topology and affect the motion of domain walls, to some extent, by means of pinning. In summary, it is concluded that in amorphous alloy ribbons the value of Kus determined by torque magnetometry does not reflect the real magnetic anisotropy which governs the magnetisation process. It mainly reflects the surface shape anisotropy