Research On Magnetization Reversal Driven By Spin-orbit Torque

Recently,the current-driven spin transfer torque magnetic random access memory(STT-MRAM)and spin-orbit torque magnetic random access memory(SOT-MRAM)have changed the traditional way of magnetic field driving magnetization reversal,thus the energy consumption of system is greatly reduced and the switching time is shorten,which are expected to be the new generation of magnetic random access memory.Based on Landau-Lifshitz-Gibert(LLG)equation and macrospin model,the trajectories of magnetic moments are simulated under spin transfer torque(STT)and spin orbit torque(SOT)in this paper.The main content of this paper is as follows:First,we introduces the research background and significance of MRAM,and briefly describe the development process and related content of MRAM.Second,on the basis of SOT-MRAM,we discuss the influence of the current direction in heavy metal layer on the magnetization reversal.The results show that,current directions have a significant effect on the magnetization reversal for magnetic tunnel junction(MTJ)with in-plane magnetic anisotropy;however,the current directions have no effect on the magnetization reversal for MTJ with perpendicularly magnetic anisotropy.Third,based on the perpendicularly magnetic tunnel junctions,we analyze thecurrent driving the magnetization reversal when different external magnetic fields are exerted,and find the critical switching currents corresponding to different fields.Eventually,the free-field critical switching current is obtained using fitting method.Fourth,in order to shorten the switching time of magnetic moment,we study the magnetization reversal driven by SOT and assisted by STT.The results show that STT-assisted SOT has obvious effect on MTJ with in-plane magnetic anisotropy,but it is not ideal for MTJ with perpendicularly magnetic anisotropy.Fifth,when the buffer layer being added into MTJ with perpendicularly magnetic anisotropy,the easy axis of magnetization would deviate from the z-axis and form a cone state structure.The results show that the azimuthal angle has a great influence on the magnetization reversal.Magnetic moment can be reversed without an external magnetic field when the azimuthal angle is approximately equal to 90°.