Effect of helical-induced anisotropy on the magnetoinductance response of Co-based amorphous wires

Abstract

In this letter, the effect of helical anisotropy, induced by torsion strain, on the circular permeability μφ, of a vanishing negative magnetostrictive CoFeSiB wire is presented. As a function of a dc applied magnetic field, Hdc, μφ shows an asymmetric behavior dependent on the direction of the applied torsion strain: for counterclockwise torsion angles (−), a monotonous decrease in the μφ (Hdc) double peak magnetoimpedance response is observed together with a linear increase in the wire’s circular anisotropy field Hk. In contrast, for clockwise torsion angles (+), a gradual suppression of the μφ (Hdc) maxima was evident, for which a magnetic softening of the wire is assumed. Results are interpreted in terms of a counterbalance/enhancement effect of the wire’s circular anisotropy for + and − torsion angles, respectively.

Helical anisotropy and magnetoimpedance of CoFeSiB wires under torsional stress

“…However, we agree with BV [3] interpretation of the MI asymmetry in terms of a residual torsion stress ð$150 MPaÞ that is enhanced or counterbalanced (since H Ã ¼ 0 for s ¼ À150 MPa) with an applied positive or negative torsional stress. The origin of the asymmetry was interpreted by Freijo et al [15] on the basis of the exchange coupling between the wire axis core, axially magnetized, and the rest of the volume carrying a circular magnetization.…”

“…[3]. Using a wire radius of a ¼ 60 mm and a length of l ¼ 10 cm, we obtain G ¼ 100 GPa which is a little different from the value used in Ref.…”

“…This model allows the extraction of the relevant physical parameters of the wire and explains the observed behavior in the cited work [3] as a function of the static magnetic field for all torsion angles.…”

“…Interpreting the asymmetry in terms of residual anisotropies induced during wire fabrication [3] leads to an effect that, respectively, counterbalances or enhances the wire circumferential anisotropy with positive or negative torsional stress.…”

“…Experimental results of the anisotropy field H Ã versus stress as obtained by BV[3] from the field value of H DC at MI peak value and theoretical lines for variable circular anisotropy field H K at zero-stress. As H K is decreased from 100 A/m (upper line) to 50 A/m and finally 25 A/m (lowest line) we get a weaker tapering off of the line for negative stress s and better fitting of the experimental results.…”