The effect of torsion stress on the circumferential permeability of CoFeBSi amorphous wires

In this paper, a domain model and the complex inductance formalism are employed to study the effect of torsion stress on the low-frequency magnetoimpedance (MI) response of CoFeBSi amorphous wires (125 μm in diameter). In particular, the torsional dependence of the calculated circumferential permeability μ_φ is found to be very sensitive to the wire´s scalar permeability μ_dc which, in turn, depends inversely on the wire´s induced anisotropy K_i. Calculated μ_φ exhibited a marked increase for increased μ_dc and a decrease for reduced μ_dc. Experimental spectroscopic plots of μ_φ under various torsion stresses (counter- and clockwise-oriented) which resulted in various helically induced anisotropies K_h are consistent with an enhancement/counterbalancing effect of K_i through the addition/subtraction of K_h to K_i.