| With the advent of the era of big data and artificial intelligence,people have higher and higher requirements on the performance of microelectronic devices.However,due to quantum effects and high power consumption,the traditional microelectronic devices that rely on the degree of freedom of electrons charge have a bottleneck in miniaturization and integration.Therefore,it is necessary to develop new electronic devices that can break through the bottleneck of traditional microelectronic devices.A new electronic spin device developed by using electronic spin has the advantages of low energy consumption,high integration,and fast processing speed,which is expected to break the bottleneck of traditional devices and become a new generation of electronic devices.High-performance devices require superior materials.Two-dimensional magnetic materials are considered as the most ideal materials for spintrionic devices because they have many excellent properties and are easy to control compared with bulk materials.In this thesis,the magnetic and electronic properties of VTe2,as well as the evolution of its magnetic and electronic properties under strain,electronic doping and interface effects,are systematically studied by first-principles methods.The research results are as follows:1.By calculating the magnetic configurations of 1T-VTe2 2×2,3×3 and 4×4 supercells,we have determined that the magnetic ground state of VTe2 P(?)m1 phase is an sAFM-type antiferromagnetic metal.Three metastable phases of VTe2 with different magnetic configurations and different electronic structures are predicted,such as:P3m1 FerriM halfmetal,P21/m dAFM semiconductor,C2/m zAFM semiconductor.2.For the P3m1 ferrimagnetic half-metallic phase,we have performed more detailed studies,including the evolution of electronic structure,magnetic anisotropy and the nearestneighbor exchange coupling coefficient under biaxial strain,and the simulation of the Curie temperature.It is found that under 5%biaxial tensile strain,it can still maintain half-metallicity,but the band gap is slightly reduced;and the magnetic anisotropy energy is greatly improved,about 2 times of the pure system.When it is compressed,it transforms from a ferrimagnetic half-metal to a ferrimagnetic metal,and its nearest-neighbor exchange coupling coefficient decreases linearly with the increase of the compressive strain.The Curie temperature of the P3m1 ferrimagnetic half-metallic phase simulated by Monte Carlo simulation is about 200 K,which is higher than that of most monolayer materials prepared by experiments.3.VTe2 can be transformed from C2/m zAFM semiconductor to P3m1 FerriM halfmetal by 0.1 e/f.u.electron doping,while 0.1 hole/f.u hole doping can induce C2/m zAFM semiconductor changes to P(?)m1 sAFM metal.They have different Fermi levels and different electron structures,so the cost of introducing electrons or holes is different,leading to different phases that tend to be formed under different carrier concentrations.The diverse electronic and magnetic properties of VTe2,as well as its response to strain and electronic doping,suggesting that the system has strong spin,charge and lattice coupling.4.We construct a 1T-VTe2/CrI3 heterojunction and find that VTe2 exhibited half-metallic properties in the heterojunction.Through the analysis of electrostatic potential and Bader charge,the phase transition of VTe2 from metal to half-metal is not due to a strong interfacial effect.The interface interaction only plays a driving role,inducing VTe2 to undergo the transition from P3m1 metal to P3m1 half-metal.Therefore,we believe that P3m1 half-metal VTe2 can be prepared experimentally by using CrI3 as the substrate.5.The VTe2/CrI3 heterojunction can be transformed from half-metal to bipolar magnetic semiconductor by hydrogen intercalation.Half-metal with different spin polarization directions can be obtained by shifting the Fermi level of bipolar magnetic semiconductors by applying gate voltage(carrier doping). |
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