High-frequency Magneto-impedance Effect Of Amorphous Materials And Its Applications In Magnetic Sensing Technology

Weak magnetic field detection has shown great application and research value in non-destructive measurement,underwater target detection,biomedical,aerospace and other fields.By measuring and analyzing these weak magnetic signals,a series of information including the magnetic and non-magnetic parts can be obtained.Presently,the commonly used weak magnetic detection methods mainly include Hall sensor,magnetoresistance（MR）,optical pumping magnetometer（OPM）,fluxgate magnetometer,superconducting quantum interference devices（SQUIDs）,etc.Among these methods,the MR and hall sensors show their light-in-weight,convenience in measurement but have failed because of low accuracy.Whereas the other methods possess high sensitivity and good real-time performance,but they together with problems like high costs,bulky size and complexity.In the past 30 years,the so-called giant magneto-impedance effect（GMI）discoveried in some certain soft magnetic alloys which with high permeability,due to the extremely high sensitivity response of alloys’impedance to weak magnetic fields,proved its great application potential in the weak magnetic detection field.At the same time,the GMI magnetic sensor shows a better cost-effective ratio due to its low cost,low power consumption,high sensitivity,simplicity and universality,and random in operating conditions.Thus,this dissertation mainly investigates the magnetic devices based on the GMI effect.From the view of physical mechanism,GMI effect and impedance Z are manily related to magnetic induction effect,especially the skin effect,of which the skin effect is mainly determined by permeability and conductivity.For a given magnetic material,conductivity is almost unchangeable,thus,any methods that can change permeability will cause the variation of GMI effect.Therefore,a lot of reasearch works have been reported.In experiments,the GMI effect in Fe-or Co-based amorphous alloys and film systems has been widely concerned:（1）Scholars mostly improve the transverse permeability and thus the GMI effect of amorphous soft magnetic alloys through current annealing,magnetic field annealing,stress annealing,electro-plating magnetic or non-magnetic layers,construction of Meander inductance structure,etc.,methods.While as a key factor which may affect the GMI effect,the shape effect and demagnetization effect of amorphous alloys themselves are less concerned.At the same time,under the premise of skin effect,GMI effect itself is essentially a kind of surface phenomenon.Thus the surface conditions and direct surface treatment of the amorphous material have a non-negligible influence on its GMI effect.This has became another point to further enhance its GMI effect.（2）Among the film systems,Scholars mainly assemble Fe Ni,Co Fe B,Co Si B,Fe Si B,etc.,films into“sandwich”multilayer film to improve the magnetic permeability through interlayer coupling,thus to obtain high GMI value.Single layer films are usually use high permeability Co Nb Zr alloys instead,the material contains noble metals like Nb,Zr,etc.Which eventually,on the one hand,makes the manufacturing procedure of GMI devices complicates,on the other hand,the expense also increases.（3）In addition,in magnetic detection technology,sensor range is also a very important parameter.As a means of magnetic detection,GMI sensor range,especially the range-adjustable GMI sensor,is almost unknown.Based on the above problems,this dissertation mainly does the following researches:1.Research on GMI effect and application of Co-based amorphous ribbons.（1）The Co-based ribbons were transverse patterning and side curve demagnetization optimization treatment respectively.And the influence of both treatments on magnetism and GMI effect were investigated.The results indicated that:transverse patterning treatment brings the transverse GMI value from～3%to～50%,while degrade the longitudinal GMI value from～180%to～40%,which is mainly related to the change of permeability caused by the competition of shape anisotropy in the two directions;At the same time,during the side curve treatment,the convex optimization and the single curve optimization enhance the GMI ratio of about 10%as compared with un-treated Co-based ribbon.While the two curves optimization and the three curves optimization increase the GMI value by～14%.Besides,the curve optimizating height h_out and h_inalso help in improving the GMI ratio.These changes are mainly related to the magnetic variation caused by degradation of demagnetization effect,especially the permeability changes.（2）The Co-based amorphous ribbbons was surface treated by ion beam（IBE）and electrochemical methods,respectively.And the influence of both methods were investigated.The results shown that:after IBE treatment,the GMI ratio decrease from～152%to～90%.However,after shorter times(t_poli≤t_cri)of electrochemical treatment,the GMI ratio increase from～210%to～270%,while longer time degraded the GMI effect.This is mainly related to the change of stress and permeability.Finally,a phenomenological mode based on the stress redistribution caused by the surface quality and thickness thinning of the sample is proposed.（3）Combined with simulation and experiment,a Co-based amorphous GMI device with toroidal inductance structure is constructed,the GMI effect and current sensing performance were investigated.2.Based on the fact that the Fe₆₅Co₃₅ alloys has a high B_s of～2.45 T and is expected to obtain very high magnetic permeability through doping,the effect of N doping and thickness on the high frequency impedance and GMI effect of Fe Co N monolayer films were systematically studied.In addition,based on the fact that the“ferromagnetic/anti-ferromagnetic”system is expected to induce the exchange bias to further increase the“GMI-H_dc”response linearity and detection range,the dissertation also investigate the GMI effect in the"Fe Co N/Fe50Mn50/Ta"multilayer.The final results shown that:the Fe Co N monolayer with N doping concentration of 6%and thickness of 300 nm has a maximum GMI value of 39.71%,which is nearly eight times of the 5.9%GMI value in Huimin Yuan’s Fe Zr BNb monolayer,and is very close to the GMI value（37%-60%）of（Fe Ni/Ti）₄/Fe Ni multilayers after annealing by San Sheng Wang.However,the GMI ratio is very small in multilayer’s system due to the amorphous state Fe Co N and the signal leakage caused by Ta layer.3.High frequency Z measurement among GMI effect characterization of film is also a problem to be solved.Based on the simulation and design of"open"type microstrip line fixture,the dissertation also deduces and gives the Z extraction method.4.At last,a GMI magnetic sensor with range-adjustable based on the"Electro-striction/Inverse magnetostrictive"coupling effect was constructed.Combined with theoretical and experimental measurement,the magnetic detection performance of the"PZT ceramics actuator/Fe-based amorphous ribbon"range-adjustable GMI magnetic sensor was investigated.Which provides an idea for the future construction of high-performance GMI magnetic sensors that take into account both“weak magnetic field detection”and“conventional large magnetic field detection”.