Anisotropy distribution and magnetoimpedance in stress annealed amorphous ribbons

The magnetic anisotropy and the magneto-impedance of stress annealed FeCoCrSiB amorphous ribbons have been studied. Selected heat treatments have been choosen in order to induce, at different conditions, the same value of transverse induced anisotropy constant. These samples, showing nearly identical longitudinal hysteresis loops, exhibit different MI maximum value, MI curve shape and MI hysteresis. These results can be explained assuming a distribution of induced magnetic anisotropy constants, whose parameters depend on the heat treatment conditions. It is shown that even in the absence of the anisotropy distribution, theoretical magnetoimpedance ratio never reaches an infinite value when applied field equals the anisotropy field of the sample.