First-principles Investigations On Electronic Structure And Magnetic Properties Of Two-dimensional Magnetic Materials

With the rapid development of microelectronics technology and device integration,two-dimensional（2D）materials play an important role in nanoelectronic devices.Spin devices based on electron spin degrees of freedom provide a new direction for high-density,low-power information transfer and storage technologies.Magnetic materials exhibit different physical properties at the two-dimensional scale than their three-dimensional systems,and have excellent electrical and magnetic properties,which will surely create more opportunities for magnetoelectric and magneto-optical applications.In addition,theoretical studies and predictions based on density functional theory have promoted the development of 2D magnetic materials,and many theoretical predictions have been experimentally verified.In this paper,we use density functional theory based on first-principles to study the electronic structure of the ground state,excited state and high temperature phase,and magnetic anisotropy of magnetic two-dimensional materials through several material systems such as Cr I_3.The main research contents are as follows:1.We investigate the effects of isotropic and anisotropic pressures on the atomic and electronic structures of VI₃ using first-principles methods.It is found that in-plane strain induces structural deformation,breaking the triple rotational symmetry of the lattice.Both in-plane strain and out-of-plane strain increase the width of conduction and valence bands,reduce the band gap,and change VI₃ from semiconductor to three-dimensional metal.Structural deformation is not responsible for the insulator-to-metal transition.At the same time,the calculation results of the magnetic anisotropy energy show that under the isotropic pressure,the easy magnetic axis changes from out-of-plane to in-plane.It is further demonstrated that applying external stress is an effective means to control the magnetic anisotropy.2.We apply the disordered local moment picture for describing the paramagnetic states of two-dimensional magnetic semiconductors.We calculated the electronic structure of paramagnetic phases of Cr I₃,Cr Si Te₃,and Ni PS₃ using the density functional theory with static Hubbard corrections.The semiconducting electronic structures are successfully reproduced without any inclusion of dynamical correlation effects.The local electronic structure of magnetic ions in the paramagnetic phase resembles those in the magnetically ordered phase.The band structures of the paramagnetic phases are also analyzed.The description of the electronic structure of the paramagnetic state of the material will help to deepen the understanding of magnetic order at low temperature,especially the role of magnetic order on symmetry breaking.3.We propose a completely first-principles-based theoretical framework to study spin waves in magnetic 2D materials.The spin waves of magnetic two-dimensional materials such as Cr I₃,Cr₂Br₃I₃,Cr₂Cl₃I₃ and metallic Mn Te₂,Mn Se Te and Mn STe under this theoretical framework are calculated.The calculated energy range of the spin-wave dispersion is consistent with the experimental observations.The calculated energy range of the spin-wave dispersion is consistent with the experimental observations.For 2D materials such as Mn Te₂,the spatial inversion symmetry breaking leads to an increase in the anisotropy in the spin-wave dispersion.Our results provide another option for exploring spin waves in2D magnetic materials.24 Figures,149 References.