Structural differences between the nanocrystalline soft magnetic Fe73.5Si13.5B9Nb3Cu1 and Fe86Zr7B6Cu1 alloys

Initial permeability measurements on nanocrystalline soft magnetic Fe73.5Si13.5B9Nb3Cu1 and Fe86Zr7B6Cu1 alloys revealed that, in agreement with previous studies, in the optimum annealed state, the Fe-Si-B-Nb-Cu alloy exhibits much better soft magnetic behaviour than the Fe-Zr-B-Cu alloy. On the other hand, the density remained almost unchanged upon the amorphous - nanocrystalline transformation in Fe-Zr-B-Cu whereas a significant increase (similar to2%) occurred in Fe-Si-B-Nb-Cu. From X-ray diffraction and transmission electron microscopy studies, the amount of the residual amorphous phase, the lattice parameter, the internal stresses, and the grain morphology of the crystallized phase were found to evolve differently with increasing annealing temperature for the two alloys whereas their grain sizes were nearly the same for a given annealing temperature. It is pointed out that all these observed differences may also contribute to the differences in their soft magnetic behaviour. Furthermore, an analysis of the phases in the fully annealed state gave some hints to explain the different behaviour of density upon crystallization.