Mössbauer study of amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9

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Abstract
The superior soft magnetic material, Fe73.5Cu1Nb3Si13.5B9, formed by partially crystallizing amorphous ribbons upon annealing, has been investigated using x‐ray diffraction and Mössbauer spectroscopy. The microstructure of the annealed ribbons consists mainly of DO3 α‐FeSi nanocrystallites and an amorphous phase that lies in the grain boundaries. This residual amorphous phase has a Curie temperature of about 600 K; when it becomes a paramagnet the coercivity of the ribbon increases dramatically. It follows that, in addition to the nanocrystallite grain size and the random anisotropy, the coupling between the nanocrystallites by the amorphous grain boundaries is important for the achievement of the excellent soft properties. When Cu is replaced by Ag or Ni, a higher annealing temperature is required to produce nanocrystals.