Realization of the quantum anomalous Hall effect in germanene/NiXY (X, Y = Br, I, and X ≠ Y) heterostructure through proximity coupling

Proximity-induced exchange interactions present a novel avenue for manipulating physical properties in spintronic materials. The germanene (Ge) monolayer exhibits metallic behavior, and the NiXY (X, Y = Br, I, and X ≠ Y) monolayer displays semiconducting behavior. Here, utilizing first-principles calculations, we investigate the magnetic characteristics and topological properties in Ge/NiXY heterostructures induced by proximity coupling. Phonon dispersion and ab initio molecular dynamics simulations confirm their dynamical and thermal stability. Both heterostructures demonstrate in-plane magnetic anisotropy. The critical transition temperatures for Ge/NiBrI and Ge/NiIBr reach up to 108 and 85 K, respectively. With spin–orbit coupling, the Ge/NiBrI heterostructure exhibits half-metallicity, whereas the Ge/NiIBr heterostructure possesses a bandgap of 20.3 meV. Their electronic properties are robust against variations in the Hubbard U values. Remarkably, the Ge/NiIBr heterostructure hosts the quantum anomalous Hall effect with Chern number C = −1, and the easy magnetization axis transitions from in-plane to out-of-plane upon modulation of the interlayer distance. These results establish a versatile platform for proximity coupling engineering and enable practical quantum anomalous Hall devices.