Ageing-induced soft magnetic properties of an amorphous Fe-Si-B-Nb alloy

The ageing behaviour of an amorphous Fe80Si6B10Nb4 alloy has been investigated using differential scanning calorimetry (DSC) and several soft magnetic measurements. The form of the DSC curve was almost the same as that of an amorphous Fe73.5Si13.5B9Nb3Cu1 alloy, suggesting that both alloys possess essentially the same amorphous structure. For the Fe80Si6B10Nb4 alloy, a marked enhancement of the effective permeability mu(e) was achieved prior to nanocrystallization, whereas the Fe73.5Si13.5B9Nb3Cu1 alloy exhibited such mu(e) behaviour only in the nanocrystallized state. On comparison of these results, it is considered that the mechanism controlling the ageing-induced soft magnetic properties in amorphous Fe-based alloys differs from that of the random anisotropy model which has been proposed.