Nanocrystallization of ferromagnetic Co-rich amorphous alloys and magnetic softening

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Abstract
Ultra-fine grain structures were obtained in soft Co-based amorphous alloys subjected to suitable heat treatments within a restricted range of temperatures which begins well below the conventional crystallization temperature, , of the alloy. These structures lead to superior soft magnetic properties and consist of magnetic nanocrystallites with an average grain size in the range 10 - 12 nm embedded within a residual ferromagnetic amorphous matrix. The results refer to amorphous ribbons of Vitrovac 6025, which were obtained by the single-roller quenching technique and had the nominal composition . With regard to the coercive field and the initial reversible permeability, the best softening nanocrystallization effects occurred in toroidal samples heat treated for about half an hour at around . For the amorphous alloy, the nominal values of (the Curie temperature) and are 210 and , respectively. The results are interpreted on the basis of the random anisotropy model generalized to two-magnetic-phase systems.