Electronic Correlations Control Interlayer Coupling and Magnetic Transition in MnBi${}_2$Te${}_4$/MnBr${}_3$ Heterostructure

Bulk MnBi${}_2$Te${}_4$ (MBT) is an intrinsic antiferromagnetic topological insulator. However, its low Néel temperature of $\sim 25\mathrm{K}$ severely restricts its practical applications. Here, we propose a van der Waals heterostructure composed of monolayer MBT (ML-MBT) and monolayer MnBr${}_3$, an intrinsic Chern insulator possessing a high Curie temperature ($T_{\mathrm{C}}\sim 200\mathrm{K}$). By employing density functional theory calculations and Monte Carlo simulations, we demonstrate that interfacing ML-MBT with MnBr${}_3$ significantly enhances the $T_{\mathrm{C}}$ of ML-MBT by a factor of four to five. Electronic correlations characterized by the Hubbard parameter $U_2$ for Mn-$d$ orbitals in MnBr${}_3$ play a crucial role in governing magnetic coupling within the system. At a moderate correlation strength of $U_2=3.0\mathrm{e}\mathrm{V}$, slight structural distortions in MnBr${}_3$ break intralayer symmetry, enabling robust interlayer ferromagnetic coupling and yielding a single, unified magnetic transition. Increasing $U_2$ reduces these structural distortions, weakens interlayer coupling, and induces two distinct magnetic transitions, indicating interlayer magnetic decoupling. Thus, the MBT/MnBr${}_3$ heterostructure offers a novel approach for controlling magnetic order and enhancing the performance of spintronic devices.