Modulation On Electronic Structure Of Two-Dimensional Intrinsic Magnetic Semiconductor MnPSe₃ And CrI₃

Two-dimensional(2D)intrinsic magnetic semiconductors combine the characteristics of semiconductors and magnetic materials,which are one of the hottest materials in the fields of condensed matter physics and materials science.The spintronics devices based on them have the advantages of low consumption,high speed and small size.Generally,most of 2D semiconductors are nonmagnetic,where the magnetic characteristic can be induced by doping and other external stimuli.Hence,2D intrinsic magnetic semiconductors are necessary in practical applications.In this dissertation,the typical 2D intrinsic antiferromagnetic(AFM)MnPSe₃ and ferromagnetic(FM)CrI₃ semiconductors are studied systematically.The electronic structure,magnetic property and valley characteristic of monolayer MnPSe₃ and CrI₃are calculated using density functional theory by considering strain,doping,electric field and interfacial hybridization.The results facilitate the promising applications of2D intrinsic magnetic semiconductors in highly efficient spintronic and valleytronic devices.The main results of the dissertation are as follows:(1)The strain effect on the electronic structure and magnetic property of monolayer MnPSe₃ is investigated.A biaxial tensile strain of 13%can trigger an AFM-FM magnetic phase transition in monolayer MnPSe₃.The underlying physical mechanism of the strain-dependent magnetic ordering is elucidated.(2)The electronic structure and magnetic property of5d transition-metal substituted monolayer MnPSe₃ are investigated.Specific 5d transition-metal impurities can bring out half-metallicity and spin-valley coupling in monolayer MnPSe₃.By considering spin-orbit coupling,spin and valley splittings appear simultaneously in Hg-substituted MnPSe₃.Therefore,Hg-substituted MnPSe₃can be regarded as a ferrovalley material,which has potential applications in the valleytronic devices.(3)A novel spin splitting appears in the 2D MnPSe₃/Mo S₂ van der Waals heterostructure with specific stacking patterns,and the opposite spin orientations at valleys can be observed by transforming the configurations.(4)The electronic structure of 2D MnPSe₃/Cr Si Te₃ van der Waals heterostructure is investigated by considering strain and electric field.The band alignment of heterostructure can be tailored by tensile strain or electric field.The efficient band structure modulations via external stimuli provide guidance for future development in novel electronic devices.(5)The valley polarization and magnetic property of monolayer MnPSe₃ on a ferroelectric YMn O₃ substrate are investigated,where the valley-ferroelectricity coupling is predicted.The mechanism of valley-ferroelectricity coupling is further elucidated.Moreover,the conductivity and magnetism of monolayer MnPSe₃ are effectively modulated by the magnetoelectric coupling.(6)The electronic structure of 2D CrI₃/Ag Bi P₂Se₆ van der Waals heterostructure is investigated,where the ferromagnetism,ferroelectricity and ferrovalley exist simultaneously.So,this heterostructure is predicted as a triferroic system.The control of the valley degree of freedom is realized in the triferroic system,which provides a new material system for the electric field controllable anomalous valley Hall effect.