Power losses versus stress and temperature in soft amorphous alloys

Abstract

The role of stress-induced anisotropy on magnetic power losses has been investigated in FeBSiC amorphous ribbons, in the ‘‘as-quenched’’ state and after annealing. Loss separation has been accomplished up to 400 Hz, under a wide range of applied tensile stresses (3.5 MPa≤σ≤300 MPa). It is found that, by increasing σ, the hysteresis loss component Wh is initially decreased and passes through a minimum around a critical stress σ0. Correspondingly, rearrangement of the maze domain structure associated with the unstressed state occurs and a longitudinally oriented pattern sets in. The dynamic loss exhibits a somewhat opposite trend, as it tends to monotonically increase with σ, thus attenuating the overall benefits of tensile stressing. Insight on the physical mechanisms responsible for these phenomena is obtained by measuring, at different stress levels, Wh versus temperature (20 °C≤T≤280 °C). Topological rearrangements of the domain structure and interaction of the Bloch walls with localized stress fluctuations are envisaged, in association with roughness of the ribbon surface, as the main sources of coercivity and losses. As to the relaxation aftereffect, this is shown to produce additional loss under fairly restricted conditions of temperature and magnetization rate.