Spin-orbit Torque Induced Magnetization Switching In Synthetic Antiferromagnetic And Its Application In Sensor

In recent years,the spin-orbital torque（SOT）effect in heterostructures formed by heavy metals,topological insulators or antiferromagnets and ferromagnets has become an efficient method of manipulating magnetization,which has been successfully used to reverse magnetization and drive domain wall motion.SOT has the characteristics of high speed and low power consumption in driving magnetization switch,which greatly promotes the development of spintronic devices.In addition to the application of SOT,researchers also actively explore new material systems to improve the performance of spintronic devices.Compared with the traditional single ferromagnetic layer,the synthetic antiferromagnetic combines the advantages of zero stray field and high thermal stability of antiferromagnetic,and its antiferromagnetic exchange coupling field can reach several thousand Oe.It has become an important candidate material for spintronic devices,for example,the synthetic antiferromagnetic structure can be used as a free layer of magnetic tunnel junctions to improve thermal stability and reduce critical switch current.It can also be used in the reference layer of the magnetic sensor to obtain a larger magnetic field response range.Because of the high efficiency of SOT switch magnetization and the advantage of the synthetic antiferromagnetic structure in application,we study the magnetization reversal of the synthetic antiferromagnetic structure driven by SOT.Furthermore,we use the synthetic antiferromagnetic structure as the reference layer of spin valve and realize the giant magnetoresistance sensor of Wheatstone bridge structure by SOT driving the synthetic antiferromagnetic structure magnetization reversal.The main research contents and results are as follows:1)Perpendicular magnetic anisotropic synthetic antiferromagnetic（P-SAF）structures based on Co/Pt multilayers were prepared,with a maximum antiferromagnetic exchange coupling field of 10.7 k Oe.The current induced magnetization switch behavior of P-SAF structure is studied.The critical switch current density of P-SAF structure is 2.4×10¹¹ A/m²,which is like the critical switch current density of single-layer ferromagnetic layer.In addition,we also study the dependence between current-driven magnetization switch and the auxiliary magnetic field in the external surface and find that the polarity of current-driven magnetization switch changes with the magnitude of the auxiliary magnetic field.The analysis shows that the abnormal magnetic switch behavior can be explained by modulating the asymmetric domain expansion or contraction caused by the chiral domain wall motion,that is,the direction of the magnetic switch depends only on the relative velocity of the domain wall motion.2)Implement the full Wheatstone bridge sensor in Co/Cu/Co and P-SAF/Cu/Co spin-valve structures.The spin current generated by the heavy metal Pt inserted at the bottom of the spin valve drives the magnetization of the reference layer（Co or P-SAF）to switch,so that the magnetization direction of the adjacent bridge arms in the structure of the bridge is reversed,forming a full Wheatstone bridge sensor.The sensor shows line responses to the out-of-plane magnetic field with dynamic ranges from several hundred to thousands Oe.Finally,we present the prototype device structure of TMR magnetic field sensor with out of plane vertical linear response and full Wheatstone bridge structure.We believe that this device has good application value in current sensor and three-dimensional magnetic field detection.