Torsion dependence of domain transition and MI effect of melt-extracted Co_68.15Fe_4.35Si_12.25B_13.25Nb₁Cu₁ microwires

We present the torsional stress induced magnetoimpedance (MI) effect and surface domain structure evolution of magnetostrictive melt-extracted Co_68.15Fe_4.35Si_12.25B_13.25Nb₁Cu₁ microwires. Experimental results indicate that the surface domain structures observed by magnetic force microscope (MFM) transform from the weak circumferential domain of as-cast state to the helical domain under large torsional strain of 81.6 (2πrad/m). Domain wall movement distorts at torsional strain ζ = 20.4 (2πrad/m) and forms a helical anisotropy with an angle of around 30° versus axial direction of wire. At 15 MHz, the maximum of GMI ratio ΔZ/Z(%) increases to 194.4% at ζ = 20.4 (2πrad/m) from 116.3% of the as-cast state and then decreases to 134.9% at ζ = 102.0 (2πrad/m). The torsion magnetoimpedance (TMI) ratio (ΔZ/Z)ζ(%) is up to 290%. Based on this large torsional strain and high MI ratio, the microwire can be as an refferred candidate for high-performance TMI sensor application.