Structural Design,Auxetic Mechanical Properties And Electronic Magnetism Of Two-dimensional Transition Metal Halide CuCl₂

Due to their excellent electronic properties,two-dimensional magnetic materials have a broad application prospect in the fields of spintronics and nano-spin devices.In recent years,two-dimensional magnetic materials have attracted extensive attention and research at home and abroad.However,there are relatively few candidates for two-dimensional magnetic materials,so it has become a hot topic in materials physics to further expand two-dimensional magnetic materials and explore their application potential.This paper adopts the structure prediction technique based on particle swarm optimization algorithm and calculation method of the first principles with density functional theory to transition metal halide Cu-Cl two-dimensional space and proposed a novel two-dimensional magnetic materials Cu Cl₂through the global search of the structure system,its related electronic properties,mechanical properties,and magnetic properties were studied.The data of structure search shows that Cu Cl₂ has P-4m2 spatial symmetry and its tetragonal lattice configuration is similar to-2D Si O₂,showing good thermodynamic,kinetic and mechanical stability.Through the study of its mechanical properties,it is found that it has a large negative Poisson ratio value（|0.4|）,which can present a flat stretch expansion（auxetic）character.It is found that Cu Cl₂ exhibits semi-metallic ferromagnetism and magnetic anisotropy with a Curie temperature of～47 K simulated by the Heisenberg model.Through crystal field theory and related calculations,it is revealed that the ferromagnetism of Cu Cl₂ is affected by Cu-Cu exchange and Cu-Cl-Cu superexchange,and the ferromagnetism is derived from p-d hybridization of Cu 3d orbital and Cl 3p orbital.The effects of biaxial strain and carrier doping on the electronic and magnetic properties of Cu Cl₂ were investigated.Under tensile strain and electron doping,the electron structure remains ferromagnetism.However,under the condition of 4%compression and 0.4holes doping,the system will become non-magnetic.Under the condition of 2%compression and 0.2 holes doping,the system changes from semi-metallic phase to metallic phase.In this paper,a novel two-dimensional Cu Cl₂ with auxetic character and ferromagnetism is proposed,which provides a candidate material for nano-mechanical devices and spin devices.