Influence of the structural instabilities on the anisotropy fields in Co-based amorphous alloys

The influence of structural instabilities, produced by thermal treatments on the magnetic anisotropy and initial permeability, is examined in a set of Go-based amorphous alloys. The analysis is made on square strips cut out from as-received ribbons in order to study the magnetic properties along two in-plane perpendicular directions having the same demagnetizing factor. Generally, in the as-received state the samples show an easy magnetization direction parallel to the original longitudinal direction of the ribbon. Annealing, performed at various temperatures, in the absence of applied magnetic fields and mechanical stresses, enhances the original anisotropy. Some exceptions are observed: in one of these alloys the influence of the annealing is very weak, whereas in another alloy the annealing treatment gives rise to a change of the easy axis from the longitudinal direction to the in-plane transverse direction. The evolution of the anisotropy field distribution with the annealing features is also evaluated. The results are discussed on the basis of irreversible changes of local atomic order.