| Spintronic devices have the advantages of multi-functionality,low energy consump-tion,and high integration density compared with conventional electronic devices,which can realize high-density information transmission,processing,and storage.A key issue is to find spintronics materials with high spin polarization conduction electrons.Among them,magnetic half-metallic and magnetic semiconductor materials have attracted the attention of researchers due to their stable magnetic properties and high spin polarization rates,and have become hot research materials,which are ideal candidates for future spintronic devices.However,most of the synthesized two-dimensional magnetic materials often have no intrin-sic magnetism,limiting their practical applications in spintronics.In this context,this thesis investigates the prediction of the electronic structure and magnetic properties of the 2D in-trinsic magnetic materials NiXCl（X=S,Se）and NiXY（X,Y=Cl,Br,I,X≠Y）monolayers based on density generalization first-principles calculations,in the hope of further broaden the family of two-dimensional magnetic materials and their applications in the field of spin-tronic devices.Firstly,the structures optimized of the ferromagnetic and antiferromagnetic states of NiXCl（X=S,Se）and NiXY（X,Y=Cl,Br,I,X≠Y）monolayers,and found that the ground states of both systems are ferromagnetic by comparing the energies.Subsequently,their stability was determined by means of elastic constants,phonon spectra and molecular dynamics simulation calculations.Secondly,based on the first-principles calculations,we demonstrated that NiSCl and NiSe Cl monolayers are 2D intrinsic ferromagnetic half-metallic with 100%spin polarization and wide half-metallic bandgaps.Based on the Heisenberg model,the Curie temperatures of NiSCl and NiSe Cl monolayers are predicted to be 311 and 180 K by Monte Carlo simulations,respectively.The electronic structures calculated used the Heyd–Scuseria–Ernzerhof（HSE06）hybrid functional indicate that the NiSCl and NiSe Cl monolayers have half-metallic bandgap-s of 1.06 and 0.53 e V and spin bandgaps of 3.40 and 2.68 e V,respectively.These results indicate that the two-dimensional NiSCl and NiSe Cl monolayers are promising half-metallic materials.Finally,The NiXY（X,Y=Cl,Br,I,X≠Y）monolayer is systematically studied,and it is predicted that the NiXY（X,Y=Cl,Br,I,X≠Y）monolayer is a two-dimensional intrinsic ferromagnetic semiconductor material with a wide semiconductor bandgap.The indirect bandgaps of monolayers NiCl Br,NiCl I,and NiBr I are 3.42,2.19,and 2.39 e V,respectively,and the magnetic moments of each magnetic atom are 2,obtained by generalized gradient approximation.We demonstrate that the NiXY（X,Y=Cl,Br,I,X≠Y）monolayers have large in-plane magnetic anisotropy energies.The predicted T(（8）values of NiXY（X,Y=Cl,Br,I,X≠Y）monolayers are predicted to be between 98 K and 308 K by Monte Carlo（MC）simulations.In addition we have investigated the modulation of the system by strain and carrier doping.The results suggest that monolayers of NiXY（X,Y=Cl,Br,I,X≠Y）may be ideal candidates for applications in nano-spintronic devices. |
