First-principles prediction of two-dimensional MnOX (X = Cl, Br) monolayers: the half-metallic multiferroics with magnetoelastic coupling

Two-dimensional (2D) multiferroics have attracted extensive attention in recent years due to their potential applications in nano-electrical devices such as nonvolatile memory and magnetic sensors. However, 2D multiferroic materials with intrinsic ferromagnetism and ferroelasticity are very rare and most of them have low Curie temperatures. Herein, by performing the first-principles calculations, we systematically investigated the electronic structure and the magnetic properties of the MnOX (X = Cl, Br) monolayers. We demonstrated that the MnOX monolayers were intrinsic half-metallic multiferroics with the coexistence of ferromagnetism and ferroelasticity. The Curie temperatures evaluated from Monte Carlo simulations based on the Heisenberg model were about 220 K for MnOCl and 210 K for MnOBr, which could be further enhanced to 235 K and 230 K by 3% tensile strain. Moreover, their ground states exhibited significant big magnetic anisotropy energies of about 0.59 meV along the z-axis for MnOCl and 0.62 meV along the y-axis for MnOBr per unit cell. The in-plane magnetic easy axis of the MnOBr monolayer can be modulated by the ferroelastic switching due to the robust magnetoelastic coupling. These findings highlight that the MnOX monolayers (with 100% spin polarizability and high Curie temperature) are good candidates for next-generation multifunctional nanodevices.