Permeability spectra study of Fe73.5Si13.5B9Cu1Nb3−xAlx (x = 0, 0.1, 0.2, 0.4, 0.8 and 1.6)

The series of Nb-poor Finemet-type alloys Fe73.5Si13.5B9Cu1Nb3−xAlx (x = 0, 0.1, 0.2, 0.4, 0.8 and 1.6) were prepared by partial substitution of Nb by Al and then were annealed at different temperatures under hydrogen protection. The effect of Al content as well as the annealing conditions on permeability spectra is discussed. It is found that (1) the initial permeabilities of the samples containing Al are greater than that of the samples without Al after isothermally annealing except for those annealed at 813 and 833 K, (2) the initial permeability (annealed at 793 K) of those containing a moderate amount of Al (x = 0.1, 0.2, 0.4 and 0.8) are the greatest compared with those annealed at other temperatures, and (3) besides the Debye-type relaxation a new relaxation peak appears in μ″-f curves and shows a tendency moving towards higher frequency with the increase of applied field amplitude, which is explained by using the domain wall motion theory in this paper. It is concluded that the initial permeability and relaxation permeability can be improved by moderate substitution of Nb by Al in Finemet type alloys and the initial permeability is dependent on the annealing temperatures. This research provides an innovative method for fabricating higher permeability soft magnetic materials at low cost; meanwhile, it is also significant in academic research.