First-principles Calculations Of Monolayers And Bilayers Properties For CrX₂?x=Cl,Br,I?

Monolayer chromium triiodide?CrI₃?and chromium germanium tellurium?Cr2Ge2Te6?with intrinsic two-dimensional?2D?magnetism have been discovered experimentally and attract significant interests.They could realize spontaneous magnetization in monolayer,which provides a new platform for understanding and engineering the low-dimensional magnetism.The discovery of 2D ferromagnetism also opens a new direction for realizing of spintronics devices.Researchers found that CrI₃ monolayer was ferromagnetic?FM?and bilayer was antiferromagnetic?AFM?.Cr I2 and CrI₃ were paramorphs.Does Cr I2 also have intrinsic magnetism like CrI₃ or possess other novel physical properties? Do other chromium dihalides?CrX₂?X = Cl,Br,I??have the same physical properties as Cr I2? We try to answer these questions in this thesis.In Chapter 1,we start from the induced magnetic response of non-magnetic 2D materials and the research methods for the magnetism of non-magnetic 2D materials.Then we introduce the 2D FM and AFM materials,respectively,particularly the progress and significance of 2D AFM materials.Finally,we point out the importance of the study of CrX₂?X = Cl,Br,I?.In Chapter 2,we focus on the theoretical methodology to obtain the various physical properties of CrX₂?X = Cl,Br,I?materials.The density functional theory is deemed a good scheme for material magnetism.Its various theoretical details are introduced,including the choice of exchange-correlation functionals,the limitation of the calculations.In Chapter 3,we calculated the electronic structure magnetic properties of CrX₂?X = Cl,Br,I?monolayer and bilayer in detail.The results of the first-principles calculation are as follows: 1)CrX₂?X = Cl,Br,I?is similar to transition metal chalcogenides?TMDs?,and the monolayer has two configurations: 1T and 2H.The 1T configuration of CrX₂?X = Cl,Br,I?is more stable,and monolayer magnetism presents antiferromagnetism;2)CrX₂?X = Cl,Br,I?show half-metal according to electronic structure;3)Strong correlation interaction has not changed the AFM properties of the monolayer structure;4)In calculating the interlayer magnetic interaction of CrX₂?X = Cl,Br,I?,we consider two different stacking: AA and AB.AB is more stable than AA,and the interlayer magnetic interaction is AFM.We predict that the CrX₂?X = Cl,Br,I?monolayers are semi-metallic AFM materials,which would help realize the 2D materials-based AFM spintronics.