Research On The Properties Of Spin Transport And Storage In Novel Topological Materials And Heterostructures

Two-dimensional materials exhibit excellent physical properties,but with the improvement of device performance requirements,people exfoliate two-dimensional materials and then stack them to form heterojunctions.Heterostructures can overcome the shortcomings of a single material and integrate multiple material properties.Besides,due to the existence of quantum effects in thin-layer materials,it can show more excellent properties.In this paper,aiming at the heterostructure of topological materials monolayer/two-dimensional ferromagnetic materials monolayer,unified modeling of heterojunctions,usied FLEUR software combined with wannier90 and wanniertool carried out simulation studies on the energy band structure,fermi arc and spin hall conductance of three heterojunctions Bi₂Se₃/Ni I₂,Pd Te₂/Ni I₂ and Pt Te₂/Ni I₂,and then used Open MX to calculate the quantum transport properties of the heterojunctions.Finally,the LLG model of MTJ is established,and mumax3 is used to study the performance of writing methods STT and SOT,and the main conclusions are as follows:（1）We propose a heterojunction composed of Bi₂Se₃ monolayer and Ni I₂ monolayer.The magnetism of topological insulators under the influence of the magnetic proximity,the heterojunction will show valley splitting phenomenon in the interaction between magnetism and strong spin-orbit.Since different spin electrons move in different directions under the electric field,the valley splitting will be controlled by the electric field.At the same time,the heterojunction has considerable SHC,which means that the strong spin Hall effect Existing,the performance of SHC at different Fermi energies proves that the SHC of the heterojunction can be adjusted through Fermi level transfer,which can use the strong spin Hall effect to efficiently convert the spin current to generate strong SOT and enhance the magnetization reversal.At the same time,the Bi₂Se₃ monolayer enhances the magnetic anisotropy of the Ni I₂ monolayer,which is more conducive to the magnetic moment inversion.However,according to the quantum transport results,the electron transmission coefficient and conductance of the heterostructure under zero bias are very small,which is not conducive to the current transport;（2）The Topological semimetals have high carrier mobility and the same topological properties as topological insulators.Therefore,topological semimetal XTe₂（X=Pt,Pd）monolayer is proposed to replace the topological insulator and form a heterostructures with Ni I₂ monolayer,comparing the electronic structure and quantum transport properties of these two heterojunctions with those based on topological insulator heterojunctions.Similar to the heterojunctions formed by topological insulators,these two heterojunctions also have a valley splitting phenomenon with adjustable electric field,and has a considerable and tunable SHC.The difference is that the zero-bias electron transmission coefficient and conductance of these two heterojunctions in the momentum space are three orders of magnitude higher than those of Bi₂Se3/Ni I₂,especially Pd Te₂/Ni I₂ is five orders of magnitude higher,which is beneficial to the conversion of spin currents.and low-power implementation;（3）The MTJ models with writing methods STT and SOT were established respectively,and the effects of magnetization direction,current density and damping constant on the magnetization inversion performance of MTJ were studied.The higher the current density,the smaller the damping constant and the better the inversion performance.The current density has an upper limit on the improvement of the inversion performance.At the same time,the flip performance of the MTJ is explored when the two writing methods work together.The in-plane magnetized MTJ significantly improves the performance when the SOT auxiliary current is relatively small,that is,the power consumption is slightly increased.The performance improvements of both are achieved on the basis of increasing power consumption during perpendicular magnetization.Then,the effect of the perpendicular magnetic anisotropy constant on the memory performance was studied.Only when the magnetic anisotropy constant is relatively large,the MTJ can achieve normal flipping,and the oscillation time after flipping will decrease with the increase of the constant.