Study On Electronic Structures And Magnetism Of Two-dimensional Ferromagnetic CrI₃ Based Van Der Waals Heterostructures

Since the successful fabrication of two-dimensional(2D)ferromagnetic(FM)monolayer CrI₃,2D FM materials are becoming an exciting research topic in condensed matter physics and materials fields.The 2D FM materials provide a good platform for people to study the fundamental physical properties of the magnetic materials under the atomic layer thickness,which is expected to be used in the design of 2D high-performance spintronic devices.With the in-depth study of 2D materials,the van der Waals heterostructure engineering has gradually attracted more and more attention.Just like building blocks,we can stack different 2D materials to form heterostructures at will under the premise of lattice matching,and the heterostructures may own novel physical properties which are different from those of component materials.The emergence of 2D FM materials undoubtedly provides a richer choice for people to construct heterostructures.In this paper,the electronic structures and magnetism of MX₂/CrI₃(M=Mo,W;X=S,Se,Te)and stanene/CrI₃2D FM heterostructures are studied using the first principle calculation method.The main contents are as follows.The theoretical model of MX₂/CrI₃2D FM heterostructures is constructed by stacking the monolayer transition metal chalcogenide MX₂vertically with the monolayer CrI₃.Due to the magnetic proximity effect,MX₂appears magnetization,and the symmetry of time inversion of MX₂is broken,so that the valley degeneracy of MX₂in K and K?valleys is lifted,that is to say,the valley polarization occurs.Moreover,the magnetization and valley polarization of MX₂are closely related to the atomic number of material elements.When the M atom is the same,the larger atomic number of X atom is,the more obvious the magnetization of MX₂is,the larger the valley polarization is;When the X atom is the same,the same law of change exists with the increase of the atomic number of M atom.This result shows that we should look for better valley polarization materials in the materials containing heavy metals.In addition,it is found that the external electric field,the interlayer coupling and the stacking mode of heterostructure can effectively regulate the valley polarization,which is helpful for the experimental research on the performance of the valleytronic devices.The stanene/CrI₃2D FM heterostructure is designed theoretically,and the value of its intrinsic valley polarization is found to be 39.6 me V.By changing the spin orientation of Cr atom in CrI₃layer,the valley polarization can be regulated regularly.When the spin direction of Cr atom is parallel to the c axis,the valley polarization value reaches 71.7 me V,while when the spin direction of Cr atom is perpendicular to the c axis,the valley polarization value is only 1.7 me V.In addition,the stanene/CrI₃heterostructure also has strong interlayer interaction,which makes it have obvious band hybridization and interlayer charge transfer phenomenon.When the spin orbit coupling is not considered,there are hole doping and electron doping in stanene layer and CrI₃layer,respectively.And stanene shows a spin polarized Dirac electron behavior.Its Dirac cone is completely contributed by the electrons of spin down state,and its cone point opens a band gap of 187.6 me V.These results indicate that the stanene/CrI₃2D FM heterostructure is very promising to be applied in future 2D high-performance spintronic and valleytronic devices..