The magnetic properties of a magnetic detector using oxidized amorphous Co95-xFe5(BSi)(x) alloys

A comparative oxidation study of several amorphous Co7-xFe5(BSi)(20+x) allo ys was carried out. Reentrant magnetization behavior and field-induced anis otropy which are of a critical importance for a magnetic detector were obta ined after oxidation of the amorphous Go-rich ribbons. During this oxidatio n, the ribbons develop surface oxides which are primarily nonmagnetic boros ilicate or a combination of borosilicate and magnetic oxides such CoO or Fe O. Beneath this lies a 100-1000 Angstrom thick Go-rich magnetic alloy which may be either HCP or FCC in its crystal structure. The thickness of the Go -crystallized layer is determined by the type of the surface oxides. The ox idation products such as appear to affect the reentrant magnetization behav ior of Go-rich amorphous alloys significantly. We have determined the amoun t of metalloids (a critical concentration of B and Si) which is necessary t o form a continuous layer of the most thermodynamically stable oxide, in ou r case borosilicate, on the surface. We also observed that there is a good correlation between reentrant magnetization and the thickness of Co layer. The best reentrant M-H loop for the magnetic detector was obtained in ribbo ns with a surface berate-rich borosilicate since it ensures conditions such as (1) metalloid depletion in the substrate and (2) formation of oxygen im purity faults in Co grains that are required for strong reentrant magnetiza tion behavior. (C) 2000 Elsevier Science B.V. All rights reserved.