Effect of annealing under torsion stress on the field dependence of the impedance tensor in amorphous wires

Abstract The total impedance tensor in a 120 μm-diameter (Co 0.95 Fe 0.05 ) 72.5 Si 12.5 B 15 amorphous wire subjected to annealing under torsion stress has been measured as a function of a DC axial field H ex with the DC bias current I as a parameter. Helical magnetic anisotropy has been induced by heat treatment under torsional stress. The modification to the impedance-field characteristics caused by a DC bias current has been investigated in conjunction with the static magnetisation processes. The combination of the helical anisotropy and the DC bias field induced by a current I results in asymmetry in the static magnetic configuration. The modifications in the impedance plots due to I are of the same kind as those for the DC magnetisation loops: with increasing I the hysteresis loop becomes narrower and asymmetrical. This shows clearly that the asymmetry in the impedance-field (MI) behaviour is related to the static magnetic structure that originates from a combination of the helical anisotropy and DC circumferential field. Introducing asymmetry enhances the MI sensitivity and is also important to realise linear sensing.