Septuple XBi2Te4 (X=Ge, Sn, Pb) intercalated MnBi2Te4 for realizing interlayer ferromagnetism and quantum anomalous hall effect

Realizing the quantum anomalous Hall effect (QAHE) at high temperatures remains a significant challenge in condensed matter physics. MnBi₂Te₄, an intrinsic magnetic topological insulator, presents a promising platform for QAHE. However, its inherent interlayer antiferromagnetic coupling hinders practical realization at high temperatures. In this study, we propose a novel approach to achieve interlayer ferromagnetic (FM) coupling in MBT bilayer by intercalating the septuple-layer of topological insulators XBi₂Te₄ (X=Ge, Sn, Pb). Using first-principles calculations, we demonstrate that the p_z orbital of the X atom mediates interactions between interlayer Mn atoms, enabling FM coupling. Monte Carlo simulations predict a magnetic transition temperature of 38 K for the MnBi₂Te₄/PbBi₂Te₄/MnBi₂Te₄ heterostructure. Our band structure and topological analyses confirm the preservation of QAHE in all MnBi₂Te₄/XBi₂Te₄/MnBi₂Te₄ heterostructures, while the MnBi₂Te₄/PbBi₂Te₄/MnBi₂Te₄ heterostructure exhibits a topological band gap of 72 meV, significantly exceeding that of the pure MnBi₂Te₄ bilayer. Furthermore, a continuum model is developed to elucidate the underlying mechanism of the nontrivial topological states. Our work provides a practical pathway to achieving interlayer FM coupling in MnBi₂Te₄ bilayers, paving the way for high-temperature QAHE and advancing the development of magnetic topological insulators for quantum and spintronic applications.