MOSSBAUER INVESTIGATION OF AMORPHOUS-TO-CRYSTALLINE TRANSFORMATION OF FE62NI16B14SI8 BY ISOTHERMAL ANNEALING

Room temperature transmission Mossbauer spectra of Fe62Ni16B14Si8 ribbons, annealed in vacuum for time periods ranging from 5 to 60 minutes at the crystallization temperature T-x = 720 K, have been used to investigate the crystallization mechanism by isothermal annealing. Reorientation of the magnetic anisotropy almost normal to the ribbon plane was observed and correlated to the annealing time dependence of the mean hyperfine field (HF) of the amorphous component. Crystallization started at the surface before the bulk and was found to occur in two steps: a metastable equilibrium of the amorphous phase with (FeNi), (FeNi)Si and t-(FeNi)(3)B, followed by the decomposition of t-(FeNi)(3)B into t-(FeNi)(2)B and (FeNi). The increase of the mean magnetic moment at the Fe sites as compared to related iron-based alloys was attributed to compositional small Ni additions.