EXCHANGE COUPLING AND MICROSTRUCTURE IN ANNEALED COBALT-RICH AMORPHOUS-ALLOYS

Low-field magnetic properties have been measured in annealed ribbons o f amorphous Co-95-Fe-x(5)(BSi)(x). The M- H loops show coercivities of order 100 mOe and weak but consistent exchange anisotropy of order 10 to 100 mOe. The direction of the field offset can be reversed by reve rsing the ribbons in the pickup coil or by applying a negative field o f order 30 to 40 Oe. We have made an extensive microstructural investi gation of these alloys to understand the origin and nature of the exch ange-coupling component responsible for the offset. Annealing in air f irst causes surface oxidation to B2O3 and SiO2 which reduces the glass -former content in the underlying amorphous material. Continued heatin g well below the built crystallization temperature results in prematur e crystallization of a layer of order 10 to 100 nm in thickness. The c rystallization product is either fcc or hcp Co (plus solutes). The fee cobalt is highly faulted which seems to be necessary for the exchange anisotropy.