Novel two-dimensional ferromagnetic materials CrX2 (X = O, S, Se) with high Curie temperature

Abstract

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials with high Curie temperature (T_C), half-metallicity, and ferroelasticity are promising for applications in spintronic devices. We propose a new kind of 2D CrX₂ (X = O, S, Se) with an orthorhombic lattice through a structural search using an evolutionary algorithm. The predicted CrO₂ and CrS₂ in the orthorhombic phase are energetically lower than previously widely studied 1T and 2H phases. They have stable dynamics, thermodynamics, and mechanics, and display ferromagnetic (FM) semiconducting, half-metallic, and metallic characteristics with Curie temperatures (T_C) of 686, 842, and 776 K, for CrO₂, CrS₂, and CrSe₂ monolayers, respectively. Carrier doping can change a semiconductor into a half-metal in CrO₂. Meanwhile, the CrO₂ and CrS₂ in FM states exhibit a significant in-plane magnetic anisotropy energy (MAE) of 99.5 and 88.5 μeV per Cr, respectively, and the CrSe₂ shows a larger out-of-plane MAE of 664.0 μeV per Cr. Moreover, the CrS₂ and CrSe₂ exhibit ferroelasticity and magnetoelastic coupling with an energy barrier of 273.9 and 174.4 meV per atom, respectively. The features of high T_C, half-metallicity, tunable magnetic properties, and magnetoelastic coupling in CrX₂ systems provide promising applications in nanospintronics.