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.
Highlights
The ferromagnetic microwires have been recognized as possessing much more promising magnetic sensing materials, especially for giant magnetoimpedance (GMI) effect, which has attracted considerable interest from the basically theoretical viewpoint and from its wide technical applicability [1,2,3,4]
As one method of the amorphous microwire fabrication technologies, different from glass-coated spinning and in-rotating water quenching techniques, the melt-extraction technique consists of the following: (i) it has the largest solidification or cooling rate, which enables the wires to possess an excellent soft magnetic property; (ii) the melt-extracted wires without glass covering are more suitable for electronic package and GMI sensor applications; (iii) the parameters of meltextraction can be conveniently controlled to produce wires with uniform diameter and roundness [6, 7]
In the intermediate frequency range (100 kHz∼20 MHz), GMI originates mainly from the variation of the skin depth owing to the strong changes of the effective magnetic permeability resulting in both domain wall motion and magnetization rotation; namely, it can be denoted by μφ = μwall + μrot [1, 8]
Summary
The ferromagnetic microwires have been recognized as possessing much more promising magnetic sensing materials, especially for giant magnetoimpedance (GMI) effect, which has attracted considerable interest from the basically theoretical viewpoint and from its wide technical applicability [1,2,3,4]. As one method of the amorphous microwire fabrication technologies, different from glass-coated spinning and in-rotating water quenching techniques, the melt-extraction technique consists of the following: (i) it has the largest solidification or cooling rate, which enables the wires to possess an excellent soft magnetic property; (ii) the melt-extracted wires without glass covering are more suitable for electronic package and GMI sensor applications; (iii) the parameters (i.e., linear velocity of wheel, feed rate of the molten, etc.) of meltextraction can be conveniently controlled to produce wires with uniform diameter and roundness [6, 7] In another perspective, near-zero magnetostrictive amorphous wires, with low resistivity ρ, high magnetic permeability μφ, high saturation magnetization Ms, and small ferromagnetic resonance (FR) in the high-frequency range, possess outstanding GMI performance. In order to understand deeply the role of the helical anisotropy to the surface domain and GMI performance of the near-zero magnetostrictive meltextracted Co-based amorphous microwires, the imposed torsional strain on the microwires is necessary to observe the domain structure by magnetic force microscope (MFM)
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