The Research Of Anisotropic Magnetoresistance Effect Based On Exchange Bias

With the rapid development of the information age,magnetic field sensors,which play a vital role in the detection and conversion of information,have attracted widespread attention from the scientific community.Among all kinds of magnetic field sensors,anisotropic magnetoresistance(AMR)sensor has become a hot research topic in the scientific community due to its advantages such as low applied magnetic field,simple preparation process,low preparation cost and easy integration,so that AMR sensor has a better market prospect than other sensors.This research mainly studies the AMR linear sensor based on ferromagnetic(FM)/anti-ferromagnetic(AFM)structure.AMR linear sensor is widely used in many fields such as navigation and positioning,vehicle detection,mineral exploration.To realize the linear detection function of AMR linear sensor,the 45° self-bias of magnetic film is core requirement.The traditional methods of manufacturing AMR linear sensor often have the disadvantages such as complex architectures,hard to integrate and high costs.Therefore,in order to solve these problems,this research introduces the FM/AFM exchange biased structure into the fabrication of AMR linear sensor.The magnetic moment of the magnetic sensing film could deflect 45° through the competition of the unidirectional anisotropy field and shape anisotropy field,and finally the AMR linear sensor is prepared.The specific research work is as follows:Firstly,based on the Stoner-Wohlfarth continuous rotation model,a single-domain model of the FM/AFM bilayer structure is established for simulation,the Matlab program is written with all the energy fields that affect the direction of the magnetic moment counted to simulate the magnetic moment orientation under different value of energy field.The simulation results show that the exchange bias field and the shape anisotropy field can greatly regulate the deflection of magnetic moment.The orientation of magnetic moment is basically determined by the direction of their combined magnetic field.The magnetic moment can achieve a deflection of 45° with appropriate NiFe thickness,width and aspect ratio of the film.Secondly,based on the theoretical simulation results above,a comparison experiment is designed to explore the deflection angle of magnetic moment under different conditions by changing the thickness of NiFe,width and aspect ratio of the film.It is found that when the exchange bias field increases from 9.52 Oe to 52.60 Oe,the magnetic moment of the magnetoresistive film with a fixed width of 20 ?m will change from 10° to 60°.When the exchange bias field is fixed at 33.44 Oe,the magnetic moment will vary from 10° to 55° as the width of the film increases from 5 ?m to 30 ?m.By comparing the linear correlation coefficient and sensitivity of the measured AMR response curve,two experimental conditions that make the magnetic moment deflect 43.15° and 42.04° are selected to prepare the AMR linear sensor of Wheatstone bridge structure.Finally,two kinds of AMR linear sensors based on the FM/AFM structure are prepared by photolithography technique.The corresponding experimental conditions are the width of the film equal to 20 ?m,the length of the film equal to 400 ?m,the thickness of NiFe equal to 30 nm and the width of the film equal to 30 ?m,the length of the film equal to 300 ?m,the thickness of NiFe equal to 30 nm,respectively.The V-H graph of AMR linear senosrs shows that they have a good linearity in the range of about ±40 Oe,the linear correlation coefficient can reach as high as 0.9947,and the sensitivity can reach as high as 0.1964 mV/V/Oe.