Oxidation of amorphous Co75.26-xFe4.74(BSi)(20+x) magnetic alloy

The oxidation characteristics of the Co-rich amorphous magnetic alloy, Co75 .26 - xFe4.74(BSi)(20 + x) were investigated. A TEM study of the microstruc ture revealed a complex oxidation behavior of the alloy depending an compos ition, especially the boron and silicon concentrations. It was determined t hat the critical concentration of the metalloid to be 21 at.% above, I whic h a continuous layer of an amorphous borosilicate phase formed on the surfa ce. Phase separation of the surface oxide was also observed when the compos ition is rich in boron. The metalloid (boron and silicon) concentration was critical in determining the surface-oxide morphology, which in turn, affec ted the subsurface microstructure. As the magnetization behavior of the Go- rich amorphous alloy depends upon the surface oxide and the internal-oxide precipitates, the guidelines ave provided by \t hich one can engineer the m icrostructure of the alloy to optimi-e the magnetic properties.