2D auxetic material with intrinsic ferromagnetism: a copper halide (CuCl2) monolayer.

The discovery of ferromagnetism in monolayer transition metal halides exemplified by CrI3 has opened a new venue in the field of two-dimensional (2D) magnetic materials, and more such 2D materials are awaiting explorations. Herein, by means of swarm-intelligence global minimum structure-searching methods in conjunction with first-principles calculations, we identified a novel CuCl2 monolayer which exhibits not only intrinsic ferromagnetism but also auxetic mechanical property originating from the interplay of lattice and Cu-Cl tetrahedron symmetries. The predicted Curie temperature of CuCl2 reaches ∼47 K, and its ferromagnetism is associated with the strong hybridization between Cu 3d states and Cl 3p states in the configuration. Moreover, upon a biaxial tensile strain or carrier doping, the CuCl2 monolayer can be converted from ferromagnetic to nonmagnetic as well as from half-metal to metal. These properties endow this CuCl2 monolayer with great potential for applications in auxetic/spintronic nanodevices.