Variation of permeability of Nb-poor Finemet under different field amplitudes

The effect of magnetic field amplitude on permeability spectra was studied by using permeability spectroscopy. Results show that the permeability spectra can be greatly affected by magnetic field amplitude—they become complicated under a higher field, which means that the initial permeability increases with an increase of the applied field at first and then decreases with further increase. Meanwhile, another relaxation peak appears and the relaxation frequency increases during the same process. In addition, the permeability is improved significantly over the basic Finemet composition with appropriate substitution of Al for Nb. Moreover, the effect of annealing condition on the permeability spectra as well as the influence of eddy current was also discussed. All these phenomena were explained by using the dynamic magnetization theory and random anisotropy model.