Surface crystallization of amorphous Fe-B-Si alloy annealed in a gas atmosphere containing organic vapour

The relationship between the annealing atmosphere and the magnetic properties of Fe_78.5B₁₃Si_8.5 amorphous alloy has been studied, showing that annealing in an inert gas atmosphere containing a borosiloxane resin significantly improves the core loss of the amorphous ribbon, and that annealing in an inert gas without any organic resins, gives much better results than annealing in an inert gas atmosphere containing cellulose and vinyl acetate resins. A boron-depletion zone was detected by Auger electron spectroscopy under the oxide film formed during annealing in the inert gas atmosphere containing cellulose and vinyl acetate resins. Annealing of the amorphous ribbon in the cellulose and vinyl acetate resins selectively oxidizes boron in the alloy to form a B₂O₃ film and a boron depletion zone; the alloy in this zone is then crystallized into -Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous ribbon and thus deterioration of the core loss. On the other hand, annealing in the borosiloxane resin results in neither selective oxidation of boron nor surface crystallization of the amorphous ribbon