A NEUTRON DEPOLARIZATION STUDY OF STRESS-ANNEALED AMORPHOUS FE40NI40B20

The three-dimensional neutron depolarization (ND) technique has been a pplied to characterize the bulk magnetic domain structure and the spat ial distribution of the magnetic anisotropy in amorphous Fe40Ni40B20, which was annealed under the application of a uniform bending stress. Such an annealing treatment results in a viscoelastic strain, which is demonstrated by the ribbon remaining curved after cooling down and re moving the applied stress. In order to perform the ND measurements the annealed ribbon had to be straightened. The bending moment necessary to straighten the ribbon introduces internal stresses which couple wit h the positive magnetostriction constant of the material to induce a u niaxial magnetic anisotropy. The ND measurements show that the bulk do main structure of the stress-annealed ribbon after straightening consi sts of two layers, corresponding to the positive and negative values o f the anisotropy constant. The application of tensile stress reduces t he thickness of the layer containing the negative anisotropy in favour of the thickness of the other layer. This allows us to scan the spati al distribution of the negative uniaxial anisotropy.