Asymmetric giant magnetoimpedance in stress-field annealed CoFeBSi amorphous ribbons

Abstract

Asymmetric GMI in amorphous Co66Fe4B15Si15 ribbons is investigated. The asymmetry comes from a ferromagnetic exchange coupling of the soft magnetic amorphous phase with a magnetically harder surface crystalline layer. In magnetic fields larger then the coercive field of the exchange bias layer (about 50 Oe) the asymmetry of GMI curve can be reversed. Hard ribbon axis anisotropy, induced in amorphous phase by the stress/field annealing, can be changed to the easy axis one by applying tensile stress. Then the originally double-peak GMI curve changes to an asymmetric single-peak one with an extremely high-field sensitivity (about 3400%/Oe) at the transition.