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

Two-dimensional (2D) ferromagnets with high Curie temperatures (TC) 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 μB per Gd atom. Besides, they both show large PMA with magnetic anisotropy energies of 0.88 and 0.85 meV/unit cell and ultrahigh TC 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 TC 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.