Experimental evidence for radial dependence of induced anisotropy in cold drawn permalloy wires

Measurements of the induced anisotropy in cold drawn niobium-silver Permalloy wires of about 1-mil diameter show that there is a marked radial dependence with the anisotropy increasing rapidly inside of the cold drawn wire. Further, most of the structure in the radial dependence of the anisotropy is removed if the wire is given a mild anneal. Measurements are made by etching away outer layers of material and using a magnetic resonance technique to measure the effective anisotropy within the skin depth below the surface of the remaining wire. The disappearance of the strong radial dependence of the anisotropy on annealing together with the behavior of the anisotropy in the annealed wire under an externally applied tension leads to the conclusion that the radial variation of anisotropy observed in the unannealed wire arises from residual stresses.