MOSSBAUER STUDY OF AMORPHOUS AND NANOCRYSTALLINE FE73.5CU1NB3SI13.5B9

The superior soft magnetic material, Fe73.5Cu1Nb3Si13.5B9, formed by p artially crystallizing amorphous ribbons upon annealing, has been inve stigated using x-ray diffraction and Mossbauer spectroscopy. The micro structure of the annealed ribbons consists mainly of DO3 alpha-FeSi na nocrystallites and an amorphous phase that lies in the grain boundarie s. 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 gra in size and the random anisotropy, the coupling between the nanocrysta llites by the amorphous grain boundaries is important for the achievem ent of the excellent soft properties. When Cu is replaced by Ag or Ni, a higher annealing temperature is required to produce nanocrystals.