Study Of The Mechanism Of Strong Magnetic Coupling Based On Kagome Lattice Electron Flat-band Two-dimensional Van Der Waals Magnetic Materials

Since the discovery of graphene in 2004,two-dimensional materials have become one of the most important research directions in the scientific community.However,researchers have found that despite some progress in the study of two-dimensional magnetic materials,there are still some key issues that need to be addressed.Among them,some two-dimensional ferromagnetic materials are structurally unstable in air,and the long-range ferromagnetic coupling is relatively weak,leading to their Curie temperature mostly being below 75K.Therefore,researchers need to explore a two-dimensional material that has both intrinsic magnetism and high Curie temperature.In this regard,the Kagome lattice is considered to be one of the typical obstructive materials because it can simultaneously possess both intrinsic magnetism and high Curie temperature,making it a promising solution to the challenges facing the study of two-dimensional intrinsic magnetic materials.Through first-principles calculations,we found that the Kagome lattice has good stability and strong ferromagnetic coupling in two-dimensional magnetic materials.In addition,we also studied the mechanism of magnetic interactions in the Kagome lattice,revealing its close relationship with material structure and geometric shape:1.By using spin-polarized density functional theory calculations,we designed a new two-dimensional material Fe₃As with a Curie temperature（T_c）that can reach room temperature.The predicted Fe₃As has strong in-plane Fe-Fe coupling,and its large magnetic anisotropy energy（MAE）helps the material maintain long-range ferromagnetic ordering,which means that Fe₃As can become an ideal platform for studying long-range ferromagnetic ordering and magnetic materials.This two-dimensional Fe₃As has both flat bands and Dirac points in its band structure.After considering spin-orbit coupling（SOC）,the Dirac points will open up and a band gap will appear,indicating that the Fe₃As monolayer is a room temperature topological material.It is worth noting that the position of the flat bands is positively correlated with the strength of the magnetic coupling,which provides theoretical guidance for further research.In addition,under the effect of biaxial strain,as the distance between the flat bands and the Fermi surface decreases,the Curie temperature gradually increases.This further demonstrates that the Fe₃As monolayer can be a promising candidate material for two-dimensional room temperature spintronics devices.2.n this work,density functional theory was applied to discover that the two-dimensional honeycomb Kagome lattice compounds V₂X₃（X=O,S,Se）are essentially ferromagnetic semimetals with a spin polarization of 100%,while also possessing Dirac points and flat bands.Additionally,it was calculated that the Chern numbers of these three materials are all non-zero,indicating that they are topological material.The flat bands in the system result in large magnetic anisotropy energy（MAE）and high Curie temperature（T_c）,endowing the system with excellent application prospects.It is worth noting that the ferromagnetic and antiferromagnetic phase transitions,as well as magnetic anisotropy and Curie temperature,of these materials are influenced by biaxial strain,thus this study investigated the effects of biaxial strain on these compounds.Moreover,it was discovered that magnetic anisotropy is also affected by biaxial strain,further indicating that the magnetic properties of these materials can be tuned by strain.Therefore,this study reveals the relationship between the magnetic and topological properties of these materials,providing new ideas and insights for their application in spin-electronics materials and devices.At the same time,it also provides new directions and challenges for further exploring the properties of these compounds and developing new spin-electronics materials.