Study Of Spin Transport Properties Of Novel Two-dimensional Magnetic Material Devices Based On MnBi₂Te₄ And FeX₂（X=Cl、Br、I）

With the progress and development of science and technology,the renewal cycle of electronic products is getting shorter and shorter,people are increasingly concerned with the multifunction and intelligence for the electronic devices.The research of novel electronic devices with small size,excellent performance,low power consumption and fast processing is an urgent demand.Two-dimensional materials have attracted extensive research due to their intrinsic unique properties such as ultra-thin thickness,ease of preparation and so on.It has broad prospects on power storage devices,intelligence instrument as well as the transformation of the solar energy.Two-dimensional materials has already become a frontier field of the condensed matter and materials physics.However,most of these two-dimensional materials are nonmagnetic and require some external conditions such as applied electric field,substrate,strain,flaws,or doping to induce magnetism.However,these conditions are not easy to achieve experimentally,which limits the application of two-dimensional materials in spintronics.Recent studies have reported the successful preparation of MnBi₂Te₄ and FeCl₂ materials with two-dimensional ferromagnetism,these materials have potential applications in the fields of optoelectronic devices,logic computing and spintronics.To promote the application of MnBi₂Te₄ and FeX₂（X=Cl,Br,I）in spintronics,we designed their spintronics devices and investigated their spin transport properties based on the density functional theory and nonequilibrium Green’s functions method.Our investigations can be useful to design the spintronics devices based on MnBi₂Te₄ and FeX₂（X=Cl,Br,I）materials.The main contents of this thesis are described in the following:Firstly,the transport properties of spin-polarization electron are investigated for the devices based on the single-layer MnBi₂Te₄ and double-layer MnBi₂Te₄,respectively.Our results demonstrate that the Cu/MnBi₂Te₄/Cu device has a certain spin filtering effect with a maximum value of 42.85%.Additionally,it is found that the Cu/bilayer MnBi₂Te₄/Cu devices manifest an obvious spin filtering effect,the corresponding spin polarization can reach to55%⁶0.7%on the condition of the bias voltage of±0.1V.The tunneling magnetoresistance of the device can reach to 50%⁷2%.When the bias voltage is larger than±0.1V,spin polarization will be shown in the antiparallel configuration of the Cu/bilayer MnBi₂Te₄/Cu device.Secondly,the spin transport properties of the monolayer FeX₂（X=Cl,Br,I）devices have been studied based on the nonequilibrium Green?s function method and density functional theory.It includes the current-voltage curve,magnetoresistance ratio,spin-dependent transmission spectra as well as the project density of states.Additionally,the structure and magnetism of the materials are also investigated.The calculated results indicate that the device has a spin filtering effect and a negative differential resistance effect as well as a very high magnetoresistance ratio（reach to 10⁷）on the condition of the applied bias voltage.The spin-polarized electrical transport properties of the magnetic tunnel junctions based on FeX₂（X=Cl,Br,I）materials are investigated.At the equilibrium state,our results indicate that the tunneling magnetoresistance of the devices based on FeCl₂,FeBr₂and FeI₂ are 3275%,2911%and3118%,respectively.On the condition of bias voltage,it can be found that the device based on FeBr₂show a conspicuous spin filtering effect,high spin polarization and tunneling magnetoresistance.As far as the devices based on FeCl₂and FeI₂are concerned,they manifest not only the excellent spin filtering effect,high spin polarization and tunneling magnetoresistance but also an excellent negative differential resistance effect.In conclusion,MnBi₂Te₄and FeX₂（X=Cl、Br、I）materials have potential applications in designing the spintronic devices.Our investigations can be useful to design the vd W magnetic tunnel junction based on the two-dimensional materials.