Vertical Magnetization Reversal Driven By Spin-Orbit Torque Based On Landau-Lifshitz-Bloch Equation

In recent years,with the development of science and technology,people have higher and higher requirements on the function of memory devices.Magnetic random access memory based on spin-orbit torque(SOT-MRAM)has the characteristics of non-volatile,reversible,high speed,low power consumption and good compatibility with the traditional semiconductor industry.It completely changes the magnetization reversal mode of traditional MRAM,shortens the time of magnetic moment reversal and reduces energy consumption.It has become a fast,efficient and large-capacity MRAM that people expect.In this paper,based on the macro spin model,the magnetization reversal driven by SOT in the vertically magnetized tunnel junction(MTJ)is simulated using LandauLifshitz-Bloch(LLB)equation.The main research contents are as follows:1.Firstly,the research background and significance of SOT-MRAM are introduced,and its development history and related contents are briefly summarized.2.Through comparing LLB equation with LLG equation,we find that the simulation results based on LLB model are close to that based on LLG model at low temperature,but at high temperature,especially close to the Curie temperature,the results based on LLG model has a larger deviation,while the results based on LLB model can more accurately show the motion of the magnetic moment.3.The macro-spin model based on SOT is introduced,and the corresponding LLB-SOT equation is derived.The mechanism of the magnetization reversal is explained in detail.4.With the assistance of external magnetic field,the influences of spin orbit torque coefficient,the magnitude and direction of external magnetic field,the magnitude and direction of current as well as temperature on the magnetization reversal are explained in detail;at the same time,the influences of each quantity on the oscillation,time and critical conditions of the magnetization reversal are found;at last,the optimal state of the magnetization reversal is found.The results show that the turnover time can be reduced by 33.3% or 73.1% when the external magnetic field is along a suitable direction or the current is along a suitable direction.The range of external magnetic field and current density to reverse the magnetic moment are also found.It is found that the faster the turnover of magnetic moment is not,the higher the current or the magnetic field is,but there is an optimal state.Three kinds of magnetization reversal modes(circular,elliptic and linear reversal)are found by changing the temperature,and it is found that there is the optimal temperature to reverse the magnetic moment when the external magnetic field and current density are constant.5.Three kinds of field-free magnetization reversal mechanism are introduced.By rotating the coordinate matrix,the influence of the angle of the tilted easy-axis on the magnetization reversal in the easy conical model is discussed.The magnetic moment can be reversed when the polar angle of the easy-axis is between 10° and 80°,the reversal is the fastest when the polar angle is 22°,and the turnover time is about 0.166 ns.In addition,the field-free flip is discussed in two cases of in-plane anisotropic field and coupling field.It is found that the magnetic moment flip time is the shortest,about0.231 ns,when the in-plane anisotropic field is 1330 m T;the magnetic moment flip time is the shortest,about 0.49 ns,when the characteristic attenuation length of the in-plane coupling field is 3.56 nm.In this paper,a new physical model,LLB-SOT model,is used.Based on the mechanism of magnetization reversal,the magnetization turnover is described in detail with and without the external magnetic field.Above research has a good reference for the design and optimization of SOT-MRAM.