The First-principles Study Of Two-dimensional Intrinsic Ianthanide Based Magnetic Materials

With the rapid development of microelectronics technology,the integration and operating frequency of electronic chips known for their high speed,high density,low power consumption,and low cost are bound to rise.However,with the end of Moore’s Law,traditional electronics that solely relies on manipulating charge properties cannot meet the needs of electronic devices.2D magnets with dual degrees of freedom of charge and spin are undoubtedly the preferred materials to solve this problem.This novel two-dimensional material with unique magnetic properties has broad application potential in future non-dissipative spintronic devices.The ideal two-dimensional magnetic materials should have the characteristics of high magnetization and stable magnetism above room temperature,but so far,most of this kind of materials are realized by introducing magnetism inside the non-magnetic materials.However,the external controlling method is difficult to accurately be achieved,so it is urgent to develop new two-dimensional intrinsic ferromagnets（two-dimensional materials with intrinsic ferromagnetism）.In addition,with the improvement of density functional theory and the rise of high-performance computer science,it has become normal to design two-dimensional materials with higher density,non-volatile and low energy consumption in theory to guide experimental synthesis.Therefore,designing two-dimensional materials with high magnetic anisotropy and high Curie temperature is crucial for developing high-density non-volatile magnetic memory devices.Based on theoretical predictions,this article investigates two new types of two-dimensional intrinsic lanthanide based magnetic materials.They have excellent metal,semi metal,or semiconductor band structures,as well as significant magnetic anisotropy and relatively high Curie temperatures,providing theoretical support for the potential applications of room temperature spintronics in the future.（1）First principles study of two-dimensional lanthanide trihalidesSince the successful synthesis of two-dimensional（2D）layered Cr I₃and Ru Cl₃monolayers,transition metal（TM）trihalides have attracted widespread attention from researchers.In this paper,based on first principles calculations,Firstly,the structural characteristics（cohesive energy,phonon spectra,and elastic constants）of 2D rare earth metal（Ln）trihalide LnI₃（Ln=Ce-Tm）monolayer were studied,and the mechanical and dynamic stability of LnI₃ monolayer were demonstrated.Subsequently,molecular dynamics simulations were conducted at a temperature of 1000 K,and the results show that they had good thermodynamic stability.Then,this paper studies the electronic characteristics of all LnI₃ monolayers by calculating their energy band structures and magnetic properties.The calculation results show that Ce I₃,Nd I₃,Tb I₃ and Tm I₃monolayers are semi-metals,while the other monolayers are broadband-gap semiconductors with energy gaps of 2.52-4.73 e V,which are very suitable for high temperature resistance and radiation resistance;Ce I₃,Dy I₃,and Tm I₃ monolayers exhibit significant vertical magnetic anisotropy（PMA）,which is very rare in 2D ferromagnets,indicating their enormous potential for application in the field of spintronics.Finally,the Monte Carlo simulation results based on the Heisenberg model indicate that the Curie temperatures of Ce I₃ and Ho I₃ are lower than room temperature,which is not conducive to the preparation of two-dimensional materials.Nevertheless,they also provide a possibility for future research.（2）First principles study of two-dimensional lanthanide trihalides doped with intrinsic magnetic LiBased on the spin orbit coupling density functional theory theory（DFT）calculation,this paper proposes several single layers of LnI₃Li_0.5 with 1T structure,namely 1T-LnI₃Li_0.5,on the basis of pure LnI₃ system.Theoretical calculations have confirmed that the LnI₃Li_0.5 monolayers are thermodynamic,kinetic,and mechanically stable at room temperature.The calculation results show that all LnI₃Li_0.5 monolayers are semi-metallic,and LnI₃Li_0.5（Tb-Tm）monolayers are antiferromagnetic.After doping with Li,LnI₃Li_0.5 monolayers perform more excellently than pure LnI₃monolayers.For example,the monolayer LnI₃Li_0.5（Ln=Pr,Nd,Pm,Tb,Dy,Er,and Tm）systems exhibit significant perpendicular magnetic anisotropy（PMA）,while the others in-plane magnetic anisotropy.In addition,according to the Heisenberg model,the Neel temperatures of single layers Tb I₃Li_0.5,Dy I₃Li_0.5 and Er I₃Li_0.5 are predicted as high as612,816 and 826 K,respectively,suggesting that the antiferromagnetism can survive at room temperature.The calculated results of this article provide a theoretical basis for further research on two-dimensional magnetic materials,which is of great significance for the development of efficient spin electron nanodevices.