Theoretical Study On The Modulation Of Magnetism In The Transition Metal Atoms Doped Two-dimensional SnSe

In recent years,diluted magnetic semiconductors have attracted much attention due to their potential applications in spin devices.On one hand,dilute magnetic semiconductors have excellent optical properties of optical transition metal ions,which can be used as optical switches,optical isolators and other optical devices.On the other hand,in the semiconductor technology,because of the dual characteristics of electronic charge and spin,it has a wide application prospect in micro nano devices and spintronic devices.Two dimensional diluted magnetic semiconductors have the advantages of easy doping,magnetic modulation and high Curie temperature compared with the three-dimensional system.For two-dimensional semiconductors,the use of magnetic transition metal atoms(TM)doping is an effective method to introduce the stable magnetic moments.The magnetic moments are usually modulable,and the Curie temperature of the magnetic system is higher.In this paper,the magnetic mechanism and modulation of diluted magnetic semiconductors formed by six kinds of 3d transition metal doped with vanadium,chromium,manganese,iron,cobalt and nickel are studied using the first principle calculation method based on density functional theory on the basis of the new two dimensional semiconductor material selenide tin.Our results show that when the transition metal is adsorbed on the monolayer tin selenide surface,the hollow position is the most stable adsorption position.When the transition metal is replaced by the Se atom,the doped TM is bonded to the adjacent four Sn atoms to form a tetragonal conical structure with the point group symmetry of C4v.When replacing the Sn precursor,the vanadium,chromium,manganese and the adjacent four Se are bonded,forming a tetragonal conical structure of C4v point group symmetry,while iron,cobalt and nickel are bonded to three adjacent Se atoms,forming a triangular structure of the group symmetry of C3v points.Through defect formation energy analysis,we found that TM substituted Sn(TM@Sn)is the energy optimal doping system.Moreover,in Co@Sn and Ni@Se systems,a shallow acceptor level is located at 0.03 eV and 0.015eV energy.This indicates that the semiconducting properties of Co@Sn and Ni@Se can be activated at room temperature to form effective P type semiconductors.Taking the most stable system TM@Sn as an example,we have studied in detail the magnetic properties and modulation of Sn diluted magnetic semiconductors.We find that TM@Sn exhibits high spin polarized stable ground state,and the magnetic moment mainly comes from TM spin polarized 3d state electrons.We used the crystal field splitting and spin exchange splitting models to analyze the hybridization of TM-3d orbital.We find that in TM@Sn,the orbital characteristics of TM-3d satisfy the Hund's rule and form the electron configuration with high spin polarization.Therefore,TM@Sn exhibits high spin polarized states,corresponding magnetic distances of 3?B?4?B?5?B?4?B?3?B and 2?B,respectively.Due to the change of the relative position between the TM and the surrounding atoms,the external electric field affects the crystal field splitting of the 3d orbit,so the modulation of the magnetic state is realized.In particular,in the Fe@Sn system,when the external electric field reaches 0.4eV/A,the local structure of the defect is transformed from the triangular structure of the C3v to the C4v tetragonal structure,and the crystal field splitting changes obviously,thus realizing the transition from the "Spin-on"(S=2)state to the "Spin-off"(S=0)state.