Structure,Magnetic Properties And Spin-Electronic Transport Of Two-Dimensional MXene Tunnel Heterojunction

Two-dimensional MXene is a new type of transition metal-carbon/carbon-nitrogen/nitride material,the earliest discovered MXene is Ti₃C₂T_x,which was obtained by Gogotsi research group of Drexel University in the United States using HF acid to selectively etch Al atoms from ternary layered precursor MAX material Ti₃Al C₂.Over the past decade,a large number of theoretical and experimental studies have been doned on MXene materials,it is found that MXene has excellent mechanical,optical,magnetic and thermal properties,et.Previous studies on MXene mainly focused on capacitors,batteries,photocatalysis,optoelectronic devices and so on.However,taking into the rich magnetic effects caused by the surface functional groups account.The MXene materials can also be applied to new mesoscopic field effect transistors,magnetic readers,information processing converters and sensors et.Becaused of reason mentationed above,this paper aims to design a new type of MXene tunnel heterojunction.In order to search for half-metallic MXene ferromagnetic layer materials,the two-dimensional monolayer MXene material Nd₂N modified by surface functional groups of-OH,O,S,F,Cl and Br were studied firstly.The next work was to study the electronic properties of bilayer Fe₂NO₂H_x/Ti₂CO₂(x=1.5,1)heterojunction.In the end,study the transport properties of van der Waals heterojunction Cr₂NO₂/Ti₂CO₂/Cr₂NO₂ studied also.Details are as follows:(1)The half-metallicity of MXene material Nd₂NT₂(T=OH,O,S,F,Cl and Br)was studied.The thermodynamic stability analysis shows that Nd₂N and Nd₂NT₂(T=OH,O,S,F,Cl and Br)can exist stably.The effects of surface functional groups-OH,-O,-S,-F,-Cl and Br in the electronic structure of Nd₂N were studied.The results show that the MXene materials with the functiona is half-metallic ferromagnetism(HMF).In such HMF,the half-matellic gap width is higher than 1.70e V and the work function is ranged from 1.83e V to6.5e V.Under biaxial strain,the Nd₂NT₂(T=OH,O,S and Br)transforms from half-metal to metal under compressive strain and from half-metal to semiconductor under tensile strain,respectively.For Nd₂NF₂ and Nd₂NS₂,the half-metallic characteristics is destroyed under both compressive and tensile strain,resulting in the transformation from half-metal to metal.Finally,the electronic properties of surface functional groups with different proportions of Nd₂NT_x(T=OH,O,F;x=0.5,1(I,II),1.5)were calculated.It was found that Nd₂NO_1.5 is semiconductor,while Nd₂NO(II)has half-metallic characteristics.However,the structures with other functional groups in different proportions showed metallic characteristics.This study shows that the new lanthanide MXene materials have high application potential in spintronic devices.(2)The structure,magnetic and electronic properties of Bilayer Fe₂NO₂H_x(x=1.5,1)/Ti₂CO₂ stacked heterostructures were investigated.The results show that the bilayer Fe₂NO₂H_x(x=1.5,1)has a half-metallic characteristic and a large magnetic moment is 11?_Band 12?_B,respectively.Four different atomic interfaces,namely Bridge(H-O),Top(H-O),Bridge(O-O)and Top(O-O)were studied.It is found that the atoms at the interface are affected by adjacent atoms,resulting in different atomic relaxation behaviors.In addition,the rehybridization caused by the interface symmetry breaking makes the atomic resolution spin moment of magnetic atoms change,and RKKY magnetic exchange exists at the interface.The results of electronic structure show that the Bridge(H-O)and Top(H-O)interfaces still maintain very high spin polarization,up to more than 90%,the Bridge(O-O)and Top(O-O)interfaces maintain 100%spin polarization.It indicates that in the application of spintronic devices,the Bridge(O-O)and Top(O-O)atomic termination may have better advantages than those of Bridge(H-O)and Top(H-O)atomic termination in the application of spintronic devices.(3)The electronic transport properties of Cr₂NO₂/Ti₂CO₂/Cr₂NO₂ heterostructures connected by MXene-based van der Waals were investigated.Under zero bias voltage,by analyzing the electron transmission spectrum coefficient and the projected density of state,it is found that when the two electrode magnetic fields are parallel configuration,the electron transmission spectrum coefficient is about 11 orders of magnitude higher than that of the anti-parallel configuration,and thus the tunneling magnetoresistance(TMR)ratio of1.92×10¹³%.The spin current and electron transmission spectra under different bias voltages are studied,when the bias voltage increases from 0 V to 0.1 V,the Cr₂NO₂/Ti₂CO₂/Cr₂NO₂magnetic tunnel junction maintains good transport properties,and the TMR ratio is estimated to remain above 7.51×10¹²%.It can be considered that the van der Waals heterojunction has the potential of excellent magnetic tunnel junctions.In general,this work study comprehensively the half-metallicity of the two-dimensional layered material MXene,the magnetoelectric properties and spin electron transport properties of the MXene/MXene heterojunction and the MXene/MXene/MXene magnetic tunnel junction,which is great help to understand the source of magnetism,the magnetic exchange and spin polarization of the heterojunction interface,and the spin electron transport efficiency of the magnetic tunnel heterojunction.It also provides theoretical guidance for the preparation of two-dimensional spintronic devices.