Torsion Dependence of Domain Transition and MI Effect of Melt-Extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1Microwires

Abstract

We present the torsional stress induced magnetoimpedance (MI) effect and surface domain structure evolution of magnetostrictive melt-extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1microwires. 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 (2π rad/m). Domain wall movement distorts at torsional strainξ=20.4(2π rad/m) and forms a helical anisotropy with an angle of around 30° versus axial direction of wire. At 15 MHz, the maximum of GMI ratioΔZ/Z(%) increases to 194.4% atξ=20.4(2π rad/m) from 116.3% of the as-cast state and then decreases to 134.9% atξ=102.0(2π rad/m). The torsion magnetoimpedance (TMI) ratioΔZ/Zξ(%) is up to 290%. Based on this large torsional strain and high MI ratio, the microwire can be as an referred candidate for high-performance TMI sensor application.