Giant Magneto-impedance Effect Of Multi-phase And Multi-layer Composite Microwires

New type GMI magnetic electrical sensors usually based on giant magneto impedance(GMI)effect materials,which impedance change significantly by a weak field.Its performance depend on the eigen properties of the magnetic-sensing GMI materials.Compared to traditional sensors,it owns high-resolution,quick-response,large working temperature zone,excellent stability and linearity and low-energy and so on.Therefore,it can be used to detect cancers,earth-magnetism navigation,and it also has been made into MRAM,magnetic brain-computer interface and robot bionic skin and so on.In this present dissertation,the basic issues of fabrication parameter optimization and eigen properties for composite GMI effect microwires were systematically investigated.As well as,based on successfully prapered the multi-phase composite and multi-layer composite microwires,we also analyses the mechanism of step by step annealing,build the 3D model of surface domain structure,also we verified the characteristic skin effect enhancement phenomena in composite microwire.Finally,working frequency at low,middle,high zone GMI composite microwire were achieved,and obtained the following results:There are two ways to fabricate the nanocrystal,one was the enhanced the nucleation energy of characteristic composition CoFeSiB melt-extraction GMI Zr-doped amorphous microwire;another was decreased the Cu wheel roating speed for tailoring the thermal distribution formed nanocrystal on the surface area of microwire.With Zr doping ratio enhance,organizational order and nanocrystal size would increase in surface area,then the volum of rotating magnetic domain increased induced by wider circular domain,finally enhance the permeability.When Zr doping atomic ratio equal to 2,the impedance ratio ?Z/Zmax can reach nearly 600%,over this ratio value the bigger nanocrystal would destroy the regular circular domain then decrease the GMI ratio.Tensile strength enhanced firstly then decreased with the doping ratio,because the nanocrystal would refined main crack in the surface area,on the other hand the bigger nanocrystal became the cr ack source.At ratio equal 2,the tensile strength over 3600 Mpa much bigger than undoping microwire.Builded the real 3D surface domain model throuth filtering progressing the orginal measurement image and combined the theroy Co-based GMI microwire.Based this 3D model,the domain width and average level of leakage field were calculated,then used them to anaylses the GMI properties influenced by related parameters.Formulated the step by step annealing program by simulation the inner temperature distrubtion and combined the DSC parameters,controled the Joule temperature in both low and high structure relaxation zone,Tg and Tx point.From SEM and TEM images of microwires,we found that the nanocrystal grown from inside to outside along with the thermal transfer direction,at last formed nanocrystal-core/ amorpohous-shell special structure,we named it as phase composite microwire.This phenomenon usually results from the enhancement of nucleation energy and thermal inhomogeneous distribution.The skin effect would be enhanced by this special structure,then increase the ?Z/Z0 was ~583% at 11 MHz.The edge dislocation around the nanocrystal induced by the quenching nuclear would increase the tensile strength,on the other hand nanocrystal grown during stretching process could prevent main crack producing.In 100 m A anneali ng stage the tensile stregth was ~4103 MPa,140 m A nearly 3917 MPa.Applied DC bias current during excitation current flow amorphous microwire in measurement impedance,the biad current value was small and inducing thermal would not change the microstructure.However,it increased the transverse domain angle then enhanced the skin effect depth.So GMI ratio ?Z/Z0 was getten by reducing zero field impedance and enhancing the increment impedance when applied external field.The highest GMI ratio ?Z/Z0 was nearly 1800 at 200 MHz.Meanwhile the bias current density over 5×107 A/m2,the processing was equal to annealing,it would induce the microstructure change.Conductor core/ ferromagnetic layer composite microwire was fabricated by DC electroplate.The better choice of layer composition was Ni80Fe20 pure alloy,when during large-scale industrial production,lowcost permalloy could be replaced that,the diameter of single crystal copper core between 100-120?m.Optimizing electroplate parameters,plating solution controled at ~60 ?,p H value at ~3.5,cathode current density at ~ 6 A/dm2,plating time at 20 min,core-layer thickness ratio at 4:1.As for the characteristic skin effect enhancement phenomena,the best GMI ratio ?Z/Zmax at extremely low frequency reach to ~3600%.With plating current density increasing,the throwing power and spherical degree would reduce,then the larger surface roughness destoried circular domain regularity decreased the GMI properties.With plating time increasing,the ferromagnetic layer thickness increased that would enhance the preferred orientation.While over the property plating time,there would be shown the hydrogen embrittlement and crack onf the layer surface because of the bigger agglomerate area.Combined the MFM images and the magnetism curves,the layer surface domain structure was research.The layer domain was circular distrbution in plane and the easily magnetized direction was circular with microwire.So it was similar to the shell domain structure of Co-based GMI amorphous microwire.Based on lower conductivity core/higher conductivity layer,reversing verification the characteristic skin effect enhancement phenomena.And based on the equation of permeability and impedance of composite microwire,the value and ratio of impedance,resistance and reactance were numerical simulated.The obvious skin effect exists after 1 k Hz,and the maximum GMI ratio ?Z/Zmax between 10-100 k Hz.However,the actual value lower than theroy value induced by the quality of the surface domain structure.