Asymmetric impedance in field-annealed Co-based amorphous wires and its bias field dependence

Giant magnetoimpedance (GMI) was measured in Joule heated Co68.18Fe4.32Si12.5B15 amorphous wires. Samples heat treated in open air showed an asymmetric giant magnetoimpedance (AGMI) behaviour. The AGMI profile, measured at selected frequency values and bias circumferential fields, can be related to the exchange bias interaction between the soft magnetic amorphous material and a harder magnetic crystalline phase formed on the surface of the wire. The present data show that AGMI behaviour take place owing to a soft magnetic layer with unidirectional anisotropy that develops in the surface of the wire.