Prediction And Modification Of Spin Electronic Properties In Semiconducting Two-dimensional Structures

With the development of society and the rise of emerging information technology,there appear new challenges for electronic devices.Traditional electronic devices work by manipulating the degree of freedom of electron charge.When the size is approaching the physical limit,the quantum effect and heat dissipation of the device seriously hinder the further improvement of device performance.Spintronic devices,working by manipulating the degree of freedom of electron,have the advantages of spin,smaller power consumption,faster data processing and higher integration density,which provide hardware support for the development of modern emerging information technology.Focusing on the research hotspots in spintronics,this paper predicts and modifies the spintronic properties in the two-dimensional semiconductor structure based on the first principlecalculations.The specific research contents and results are as follows:(1)In convential Fe/MgO heterojuction,the interfacial oxidation is not conducive to spin-state transportation.In this work,a method of inserting a B layer was proposed to prevent interface oxidation.The stability and spin-electron coupling properties of FeO/MgO,Fe/FeO/MgO and Fe/FeB/MgO heterointerfaces were explored by the first-principles simulation method.The calculation results show that the Fe/FeB/MgO heterointerface formation energy is between that in Fe/MgO and Fe/FeO/MgO heterojunctions,indicating that the B interlayer can effectively prevent interfacial oxidation and maintain a stable structure.Through the study of the interface state of ?1 electronic state,it is found that the coupling efficiency of the spin-up ?1 electronic state in Fe/MgO interface is the highest.When the interface is oxidized,i.e.Fe/FeO/MgO interface,FeO at the interface will reduce the coupling of ?1 electronic state;when inserting a layer of B atomic layer,i.e.Fe/FeB/MgO interface,?1 electronic state can not only be effectively coupled into the MgO layer,and moreover,the coupling efficiency is substantially equivalent to that in Fe/MgO interface.In short,the insertion of the B atomic layer can not only improve the stability of the interface,but also maintain the high spin-electron coupling efficiency.This study provides some in-depth analysis on interface design of tunnel junctions or spin injection junctions(2)In order to explore how the mismatch strain affects the spin electrons transport of ferromagnetic(FM)/MgO heterointerfaces,we studied the spin coupling properties of FM/MgO(FM=Fe,CoFe,CoFeB)heterointerfaces under different biaxial sttains.It is found that the majority-spin ?1 electronic state in the Fe/MgO interface is most susceptible to biaxial strain,and the interfacial spin coupling efficiency decreases rapidly with the increase of strain.The CoFeB/MgO interface,which is superior to the Fe/MgO and CoFe/MgO interfaces,can markedly maintain stable and effective coupling channels for majorityspin ?1 state under large biaxial strain.Bonding interactions between Fe,Co,and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin ?1 state,directly influencing the coupling effect for the strained interfaces.Layer-projected wave function of the majority-spin ?1 state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface,which is expected to maintain a higher tunneling magnetoresistance(TMR)value under large biaxial strain.This work reveals the internal mechanism for the state coupling at strained FM/MgO interfaces.This study may provide some references to the design and manufacturing of magnetic tunnel junctions with high tunneling magnetoresistance effect(3)In order to modulate the electronic,spintronics and optical properties of two-dimensional materials,we studied the relevant properties of single-layer GaS under external electric field.Optical absorption spectra for both E ? c and E//c directions are calculated under various external electric fields.A reversal of the dipole transition from E//c to E ? c anisotropy is found with a critical external electric field of about 5 V/nm.The band structure calculations indicate a reduction of the band gap and a transition from indirect to direct and gap in GaS ML with an increasing external vertical electric field.Decomposed projected band contributions exhibit the asymmetric electronic structures in GaS interlayers under the external electric field,which explains the evolution of the absorption preference.Spatial distribution of the partial charge and charge density difference suggest that the strikingly reversed optical anisotropy in GaS ML is closely linked to the additional crystal field which originated from the external electric field.Finally,we also found that the electric field can modulate the spin texture chirality of the conduction band and the valence band,which provides some theoretical guidance for the design of spintronic devices such as spin field effect transistors and spin LEDs.