Research On Magneto-optical Effect Of Two-dimensional Agnetic Semiconductors Chromium Trihalides

Two-dimensional materials have been widely applied in the fields of electronics,optoelec-tronics.sensors,energy conversion and storage,and biomedicine due to their abundant and excel-lent electronic,optical,thermal,mechanical,and chemical properties.CrX3(X=Cl.Br,I)mono-layers are two-dimensional materials with intrinsic ferromagnetism and semiconducting charac-ter.There has no publication devoted to the magneto-optical Kerr spectra of this compound.The magneto-optical Kerr spectra are not only a powerful tool for investigating the electronic struc-ture of magnetic materials,but also being sufficiently sensitive to probe subtle changes in a spin-polarized band structure.In this thesis,we hereby systematically study the structural,electronic,magnetic,and magneto-optical properties of CrX3 monolayers.The effects of external magnetic field and out-of-plane strain on the magneto-optical Kerr spectra in CrX3 monolayers are investi-gated in detail.We also study the relationship between the magneto-optical Kerr spectra of CrI3 and the layer number.The main research contents in this thesis are as follows:1.The structural,electronic,and magnetic properties of CrX3 monolayers are calculated using first-principles density functional theory.Based on the macroscopic linear response theory,the magneto-optical properties of CrX3 monolayers are calculated and show that CrI3 monolayer possesses the strongest magnetic anisotropy and the maximum Kerr rotation.2.The relationship between the magneto-optical Kerr spectra of CrX3 monolayers and ex-ternal magnetic field is studied via changing the direction of the magnetic field,which further verifies that CrX3 monolayers have a magnetic anisotropy with an out-of-plane easy axis.3.The effect of out-of-plane strain on the magneto-optical Kerr spectra of CrX3 monolayers is studied.Not only can the peak of the magneto-optical Kerr spectra in CrX3 monolayers but also the photon energy of the peak be tuned by changing the size of out-of-plane compressive and tensile strain.4.The magneto-optical Kerr spectra of CrI3 monolayer,bilayer,trilayer,and bulk are re-searched,which shows that the magneto-optical properties of CrI3 exhibit quantum confinement effect and the magneto-optical Kerr effect of CrI3 monolayer is the most significant.The intrinsic ferromagnetism and semiconducting character,and its strain tunable and layer number dependent magneto-optical properties making CrX3 monolayers excellent two-dimensional materials for spintronic and magneto-optical applications.The research contents in this thesis not only provide theoretical basis for the practical applications of CrX3 monolayers,but also pro-vide reference significance for the research on magneto-optical effect of other two-dimensional materials.