First-principles Calculations Of Two-dimensional Transition Metal Compounds

In the last decade,the successful preparation of graphene has led to a boom in two-dimensional(2D)materials.Among them,two-dimensional magnetic materials are of great interest because of their potential applications in spintronics.At present,some materials have been found to be the intrinsic 2D magnetic materials,and 2D magnetism could be induced by external electromagnetic fields,doping,adsorption,external stress and Van der Waals hetero-structures.It is still important to find more excellent 2D magnets for the fundamental research and spintronic application.In this paper,we systematically studied the structure,stability,electronic structure and magnetism of multilayer transition metal chalcogenides and phosphorous M_nX_n+1(M=V,Cr,Mn;X=S,Se,Te,P,As,Sb;n=2,3,4)by first principles calculations.It is found that the properties of materials highly depend on the number of layers.There are many stable magnetic semiconductors and magnetic half-metal materials in multilayer transition metal chalcogenides and phosphorous.Among them,V₂Se₃,Cr₂S₃ and Cr₂Se₃ are ferromagnetic semiconductors,and Cr₃S₄,Cr₃Se₄,Cr₄Se₅,Cr₃Te₄,Cr₄Te₅,Mn₂S₃,Mn₂Se₃ and Mn₃Se₄ are ferromagnetic half-metal materials.Further studies show that the cleavage energy of these materials is low and the properties of these materials do not change significantly under biaxial strain.Meanwhile,the dependence of the properties of multilayer transition metal compounds on the number of layers is studied for the first time,and the physical origin of the change of properties with the number of layers is explored.Compared with monolayer transition metal compounds,molecular orbital states are formed between layers of multilayer materials,and the charge distribution of inner and outer layers is different.The competition between molecular orbital splitting,crystal field splitting and bandwidth will result in richer electronic structure and magnetism.Although the charge imbalance between layers makes the exchange interaction tend to be double exchange coupling,our results indicate that the ferromagnetism of most multilayer transition metal compounds should be induced by the super exchange coupling.Considering that the Curie temperature of multilayer materials may exceed room temperature,these two-dimensional multilayer materials have good application potential.Our research not only enriches the types of two-dimensional magnetic semiconductor and half-metal material,but also provides help for the design and synthesis of more novel two-dimensional multilayer magnets.