Thermal behavior of the initial permeability in soft magnetic nanocrystalline alloys

Abstract
Initial permeability thermograms for soft magnetic nanocrystalline alloys show two characteristic peaks : the first corresponds to the Curie temperature (T_c) of the remaining amorphous phase and the second to the as-precipitated bcc phase. The former one shows a broad distribution and in general shifts with annealing towards lower temperatures compared to the T_c of the as-quenched amorphous state. The latter one is relatively sharp and shifts with annealing towards higher temperatures but disappears before reaching the T_c of the equilibrium bcc phase. The first and second peaks are explained by the effect of the inhomogeneous chemical composition of the remaining amorphous phase and by the superparamagnetic transition of the dipolar (and/or exchange)-coupled bcc nanograins respectively, both changing with the evolution of annealing.