| The successful peel of graphene has stimulated intense experimental and theoretical interest in low-dimensional materials such as silene,germanene,stannene,phosphene,transition metal disulfide(TMDs),transition metal trisulfide(TMTs),etc.2D solid materials bound together by van der Waals interaction have more abundant physical and chemical properties,which attracts much attention.Two-dimensional materials typically exhibit significantly different electronic,optical,and structural properties from bulk materials.Therefore,many two-dimensional crystals with layered structures are potential candidates for nanoelectronics and optoelectronics.With the rapid development of modern information science,semiconductor technology is seeking for small size devices with high memory density and strong processing capacity,which require materials to have more stable electrical and magnetic properties even when the size is reduced to the nanometer level.Exploring two dimensional ferromagnetic materials has become an important research topic in low dimensional condensed matter physics.Currently,although there are not many intrinsic twodimensional ferromagnetic nanomaterials,it has been found that two-dimensional materials can be spin polarized by doping or applying an external field.On the other hand,similar to twodimensional ferromagnetic materials,two-dimensional ferroelectric materials are another hot topic in the research of low-dimensional materials.Two-dimensional ferroelectricferromagnetic multiferroic materials can realize the correlation and regulation of electric and magnetic states through magnetoelectric coupling effect.For example,they can realize nonvolatile storage of read/write separation and electrical and magnetic energy conversion at nanometer scale.Therefore.it has outstanding significance for the development of nanoelectronics and low-dimensional spintronics.Based on the density Functional theory(DFT)calculation method,we investigated the structure,electron and spin polarization of α-In2Se3,and discussed the effects of hole doping and atom substitution on the physical and chemical properties of the system,and further revealed the microphysical mechanism and practical application value of α-In2Se3.Monolayerα-In2Se3 is a structure composed of five atomic layers.The center symmetry of the structure is broken in the vertical direction,so it is a polar two-dimensional material.The results show that hole doping can introduce magnetism in the double-layer α-In2Se3 system,and the spin magnetic moment can reach 0.8 μB/hole.What is more interesting is that when selenium(Se)atom is replaced by arsenic(As)atom to introduced into the hole,the magnetic properties of the system are enhanced due to interlayer charge transfer,and M>1 μB/hole.Moreover,we predict that layered α-In2Se3 can be multiferroic due to its extra-surface ferroelectric properties at room temperature.Based on this structure,a high-density magnetic memory device for pure electrical writing and magnetic reading is proposed.Under the control of gate voltage,the direction of polarization can be changed,and the molecular magnetic moments can be switched between 0 or 1.20 μB,showing very strong magnetoelectric coupling.It provides theoretical reference for experimental design and fabrication of new low-dimensional functional materials and quantum devices.This paper includes the following chapters:The first chapter is the introduction,which introduces the development status and application of two-dimensional nanomaterials,origin of ferroelectric properties and two-dimensional ferroelectric materials,research status of d0 ferromagnetism,magnetoelectric coupling effect and related materials.The second chapter is the theoretical basis of the calculation method,mainly introduces density functional theory.In the third chapter,we studied the magnetic regulation of hole-doped bilayer α-In2Se3.In the fourth chapter,we summarized the research content of this paper,and prospected the development of new two-dimensional nano functional materials. |
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