Modulation Of The Properties Of Two-dimensional Magnetic Materials Based On Surface Adsorption

With the rapid development of the information age,there is a growing demand for spintronic devices,nanoelectronic devices,and optoelectronic devices,and the emergence of two-dimensional（2D）van der Waals（vd W）magnetic materials has provided a new direction for their research and development.Traditionally,2D vd W magnetic materials have been the main candidates for the study of low-dimensional magnetic material systems.At present,many experimentally prepared 2D materials do not contain ferromagnetic order,and even if a small amount of ferromagnetic order material exists,its ferromagnetism is still not stable enough.Faced with this situation,how to regulate the magnetic properties of 2D materials has become an urgent research topic.Meanwhile,with the continuous development and progress of computer technology,the first-principles calculation method based on density functional theory plays an indispensable role in the electronic and magnetic properties of 2D magnetic materials.In this paper,a systematic study of the adsorbed atoms on the surface of monolayer Cr₂Ge₂Te₆ and 1T-CrSe₂ is carried out using a first-principles approach based on density functional theory.（1）The adsorption of H/Cl/OH atoms on the surface of the monolayer ferromagnetic semiconductor Cr₂Ge₂Te₆ is performed to investigate the modulation of its electronic and magnetic properties.In terms of electronic properties,the results show that the adsorption of H atoms can still maintain the semiconducting properties of the monolayer Cr₂Ge₂Te₆,while the adsorption of Cl/OH atoms makes it metallic.In terms of magnetic properties,on the one hand,the adsorption of H/Cl/OH atoms both keep the monolayer Cr₂Ge₂Te₆ in a ferromagnetic state.On the other hand,the magnetic anisotropy increases with the adsorption of H/Cl/OH atoms,where the magnetic anisotropy increases linearly with the increase of the adsorption concentration of H atoms,but the increase is small;with the increase of the adsorption concentration of Cl/OH atoms,the magnetic anisotropy increases up to five times of the original one,and the corresponding Curie temperature reaches the Curie temperature of bulk Cr₂Ge₂Te₆.Not only that,during this period,the transition of the easy magnetization axis can be achieved.The discovery of the regulation of the electronic and magnetic properties of the monolayer ferromagnetic semiconductor Cr₂Ge₂Te₆ provides opportunities for applications in a new generation of magnetic memories,sensors,and spintronic devices.（2）The adsorption and diffusion of Li/Na atoms on the surface of the monolayer magnetic material 1T-CrSe₂ are carried out as a way to investigate the effect on its related properties.Firstly,the adsorption of multiple Li/Na atoms on the monolayer 1T-CrSe₂ surface is performed,and the results show that the adsorbed system is still an exothermic reaction and the adsorption energy is greater than that of its adsorption on other 2D materials such as graphene and Mo S₂.Secondly,in the high concentration of Li/Na atom adsorption,the monolayer 1T-CrSe₂ appears to change from metallic to semiconducting properties,and the emergence of this emerging semiconducting property is mainly caused by the lattice expansion effect,which provides a feasible way to obtain semiconductor materials from metallic materials.Finally,the individual Li/Na atoms have small diffusion potential barriers of 0.21 e V and 0.12 e V on the monolayer 1T-CrSe₂,indicating that the Li/Na atoms can diffuse rapidly at room temperature and possess a large diffusion mobility.The modulation of the relevant properties of the monolayer magnetic material 1T-CrSe₂ offers the possibility of its future use as nanodevice integration.