Ferromagnetic GdX (X = Cl, Br) Monolayers with Large Perpendicular Magnetic Anisotropy and High Curie Temperature

Two-dimensional (2D) ferromagnets with high Curie temperatures (T_C) and large perpendicular magnetic anisotropy (PMA) are rare, but have great potential in the field of spintronics. The present work investigates the electronic and magnetic properties of GdX (X = Cl and Br) monolayers and the two layers of GdCl/GdBr heterojunctions by conducting in-depth theoretical calculations. As expected, both GdCl and GdBr monolayers are ferromagnetic and have large magnetic moments of ∼8 μ_B per Gd atom. Besides, they both show large PMA with magnetic anisotropy energies of 0.88 and 0.85 meV/unit cell and ultrahigh T_C of 826 and 704 K, respectively. Significantly, they both have topological properties and spin-orbit-induced energy band reversion. In addition, we found two stable stacking configurations for the GdCl/GdBr bilayer heterojunction. The ultrahigh T_C and topological properties are maintained in the two stacking configurations. Their easy magnetization axes shift from out-of-plane to in-plane directions as a result of the competition mainly between the Gd p and Gd d orbitals. These properties endow GdCl and GdBr monolayers with great potential for practical applications in the field of spintronic devices at the nanoscale.