First-principles Study Of Strain Impact On The Magnetic Properties Of Two-dimensional CrTe₃

Self-magnetization can be remained on atomic scale in two-dimensional magnetic materials,providing new opportunities for the research of low-dimensional systems’magnetism and potential application in information storage and data processing.In this thesis,we have studied the structural and electronic properties of Cr Te₃monolayer with strain and the effect of strain to Cr Te₃monolayer’s stability and magnetism.In the first chapter,we briefly introduce some basic concepts and theories of magnetism.Then we expound the development of two-dimensional magnetic materials and the manipulation to two-dimensional materials’magnetic materials,including strain,defect,chemical modification and electric field,before introducing the main research contents of this work.In the second chapter,we mainly introduce the first-principles methods based on density functional theory,and the calculation software employed in this work.In the third chapter,we discuss the effect of biaxial strain to the lattice structure and electronic structure of Cr Te₃monolayer.Firstly,we optimize the geometric structure of Cr Te₃bulk and analyze its electronic structure.Then we build the model of Cr Te₃monolayer and analyze its variation of bond length and bond angle with strain.Its spin-polarized band structure,along with the density of state are studied,and a transition from semiconductor to metal under 9%tensile strain is predicted.Lastly,ab initio molecular dynamics（AIMD）simulations are performed and the kinetic stability of Cr Te₃monolayer under strain are examined at room temperature.In the fourth chapter,we discuss the effect of biaxial strain to Cr Te₃monolayer’s magnetism.We firstly verify the most stable antiferromagnetic（AFM）and ferromagnetic（FM）configuration after searching out all the possible magnetic configurations in the studied Cr Te₃monolayer models.Then energy difference between AFM and FM coupling under different biaxial strain,and their spin charge densities,have been studied.A transition from AFM to FM ground state under 4%tensile strain is found.In addition,its strength of FM（AFM）coupling coupling will be enhanced with tensile（compression）strain.Its magnetic moment can also be enhanced by tensile strain.We also find that its magnetocrystalline anisotropy energy（MAE）is very small and insensitive to strain.Then we find the magnetic transition in Cr Te₃monolayer fits well with Goodenough-Kanamori-Anderson rule,which depends on the competition between direct and superexchange interaction.Lastly,the Curie temperatures of Cr Te₃monolayer under 4%and 10%tensile strain have been estimated by Heisenberg Model based Monte Carlo（MC）simulations after regressing the magnetic exchange parameter of Cr Te₃monolayer.It is found that its Curie temperature can be slightly enhanced by tensile strain but they are still far below room temperature.In this thesis,we emphasize that the effect of strain to Cr Te₃monolayer’s magnetic properties,predicting a transition from AFM to FM ground state under a range of tensile strain with its semiconductor characteristics remained.In addition,its magnetic stability and the underlying mechanism of magnetic transition are both studied.This research provides not only the theoretical basis for the application of Cr Te₃monolayer in spintronic devices,but also guides to the manipulation of two-dimensional magnetic semiconductors.