Study On The GMI Property And Modulation Of CoFe-based Melt-extracted Microwire

Amorphous microwires have excellent soft magnetic properties,especially the magneto-impedance properties of the CoFe-based melt-extracted microwires.Their high giant magneto-impedance ratio,high response sensitivity and field response range characteristics can be used for the research and development of magneto-sensitive sensors.In this article,melt-extracted Co_68.15Fe_4.35Si_12.25B_13.75Nb₁Cu_0.5amorphous microwire were adopted by the conventional and joule heat annealing step modulation joule heat annealing for giant magneto-impedance effect.By observing the magnetic domain structure at different current amplitude of joule heat annealing,the corresponding relation of GMI effect and the magnetic domain structure was trying to establish.（1）Investigate the resistance effect and magnetic domain structure of microwires after Joule heating annealing with different current amplitudes（0 mA,30 mA,40 mA,50 mA,60mA,70 mA,80 mA,90 mA,100 mA）,and obtain With the increase of the annealing current amplitude,the impedance effect presents a change law that first increases and then decreases.The impedance performance of the as-prepared microwires is not obvious,which is due to the large residual stress inside the microwires during the preparation process,and the circumferential domains on the surface of the microwires are relatively weak;after annealing with a proper current amplitude,the surface circumferential domains are distributed regularly,and significant impedance is obtained Ratio and higher field response sensitivity;and the excessive Joule heat generated by larger current promotes the obvious local crystallization of the microwire,the magnetic domain wall appears pinning,the circumferential domain is destroyed,and the impedance performance is reduced.（2）The stepped Joule heat modulates the GMI effect of the microwire,and the stepped current amplitude increases from 40mA,60mA,80mA to 100mA.With the increase of the annealing current amplitude,the impedance effect changes significantly.The impedance ratio[ΔZ/Z₀]_max（%）of 80 mA stepped annealed microwire reached 318%.The GMI response sensitivity of 100 mA annealed microwire was as high as 293.3%/Oe.The range of magnetic field linear response increased from 0.1 Oe at the prepared state to 4.4 Oe at 100 mA stepped Joule annealing.Comparing the domain structures of different modulated states,it is found that the circumferential domain is more ordered and the surface of the microwire is more smooth after 80 mA stepped Joule annealing.After 100 mA stepped Joule annealing,the circumferential domain is clearer in whole with the blurred domain structure in part,and the microwire surface modulated by higher current is slightly rough.（3）By further analyzing the variation curves of magneto-resistance[ΔR/R₀]（%）and magneto-reactance[ΔX/X₀]（%）of GMI performance,it is concluded that the variation rule of[ΔZ/Z₀]（%）is roughly similar to that of[ΔR/R₀]（%）,which is closely related to the internal local atomic distribution of the microwire.The degradation of impedance performance is also caused by the surface roughness,the shape anisotropy and domain wall pinning damage the micro-structure and domain structure of the microwire.The GMI performance is closely related to the circumferential domain of the surface domain structure of the microwire.Modulating the domain structure of the microwire is helpful to obtain better GMI effect and the application of the magneto-sensitive sensor parts.