The orientation-effect of exchange bias on giant magnetoimpedance in surface crystallized Co₆₆Fe₄B₁₅Si₁₅ amorphous ribbons

A phenomenological model to describe the transverse differential susceptibility in the field-annealed CoFeBSi amorphous ribbon is developed. The exchange bias between surface crystalline layer and amorphous bulk is described by means of an exchange bias field. The model allows one to calculate the external field dependence of the transverse differential susceptibility. It is shown that so-called valve at low frequencies and asymmetric two- peak behavior at high frequencies appear in the transverse susceptibility if the orientation of the exchange bias deviates from the ribbon axis. The calculated results are in a qualitative agreement with the magnetoimpedance profiles observed in experiments and allow one to conclude that the exchange interaction between the surface crystalline layer and amorphous bulk is antiferromagnetic coupling.