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

The total impedance tensor in a 120 mum-diameter (Co0.95Fe0.05)(72.5)Si12.5B15 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. (C) 2002 Elsevier Science B.V. All rights reserved.