Microstructural evolution of amorphous cobalt-rich magnetic alloys during magnetic field annealing

We have studied surface crystallization phenomenon in Co-rich amorphous alloys based on Co95−xFe5(BSi)x. Our results indicate that amorphous alloys can undergo surface crystallization in response to oxidation at temperatures well below the bulk crystallization temperature. We also add new details to this process, and in particular show that it involves a sequence of three steps: (1) formation of an amorphous borosilicate surface oxide layer; (2) depletion of the underlying amorphous metal of glass-stabilizing boron and silicon; and (3) primary crystallization of the destabilized, metal-enriched sub-surface layer to an fcc or hcp phase. The structure and morphology of the sub-surface crystallites depend on the Si/B ratio as well as on temperature and time.