Magnetic And Electric Properties And Regulation Of Graphene-like Nano-sheet MXene

Graphene was found in 2004,which broke the general view that any two-dimensional crystal may not exist at a finite temperature based on thermodynamic fluctuations.The excellent physical and chemical properties of two-dimensional materials have aroused a research upsurge.Any material always has defects and impurities.These defects and impurities both cause certain influence on the properties of materials.How to utilize effectively these defects and impurities to expand the application of materials has become a new research hot spot.In this paper,the first-principles calculation based on the density functional theory is mainly used to comprehensively study the atomic vacancy defects,exchange disordered Frenkel-type defects and the doping of transition metal atoms Z（Z = Sc,V and Zr）in graphene-like Ti₄N₃ monolayer MXene nanosheet.The specific work is as followed.Firstly,the geometric structure of the graphene-like Ti₄N₃ monolayer MXene nanosheet was optimized under the condition of spin polarization.Then physical properties of the optimized nano-sheet were calculated,Results show that the Ti₄N₃ nanosheet has a hexagonal lattice structure.N atoms are located in the twisted octahedron.The nanosheet has inherent magnetic distance,which is mainly derived from spin-polarized d electrons of surface Ti-atoms.Our calculated results are in good agreement with the reported experimental data.At last,the microscopic mechanism of related physical properties is analyzed.Secondly,the single vacancy defect and exchange disordered Frenkel defect effect of the graphene-like Ti₄N₃ monolayer MXene nanosheet were calculated.According to the calculated binding energy and formation energy,the structures corresponding to surface Ti and subsurface N atomic vacancy are both stable.However,the the former has lower binding energy and formation energy than the latter,showing the Ti atomic single vacancy defect is more likely to occur experimentally than N.Two atomic vacancy defects（Ti and N vacancy defects）in Ti₄N₃ nanosheet can enhance the magnetism of the material.When exchange atoms are disordered,the surface of Ti-N after exchange is disordered and unstable,and will cause the Frenkel type defect.In the Frenkel type defect system,the total magnetic moment is reduced due to the enhancement of the indirect magnetic exchange between the surface Ti atoms and theourside N atoms.Furthermore,the corresponding nano-materials are highly spin-polarized,with the spin polarization rate up to 70%.Thirdly,the physical properties of the graphene-like Ti₄N₃ monolayer MXene nanosheet doped by transition metal Z（Z = Sc,V,Zr）were calculated.Results show that all the doped structures are stable and have high magnetic moment,mainly due to the directional magnetic exchange between Z and Ti atoms on the surface.Especially,in the doped Ti₄N₃-Sc system the high spin polarizability is still sustained,which indicates that the doped system has great application potential in spintronics.