Ferromagnetic Interlayer Exchange Coupling in Magnetic Topological Insulator Sandwich Heterostructures

ABSTRACT A single septuple layer (SL) of MnBi ₂ Te ₄ is a promising 2D ferromagnetic insulator for integrating magnetism with topology in van der Waals heterostructures, using topological insulators such as the nearly lattice matched Bi ₂ Te ₃ with quintuple‐layer (QL) units. Here, electrical transport measurements are performed on 1 SL MnBi ₂ Te ₄ / n QL Bi ₂ Te ₃ /1 SL MnBi ₂ Te ₄ sandwich heterostructures ( n = 0–4) to investigate the role of Bi ₂ Te ₃ spacer thickness in tuning interlayer magnetic interactions. Magnetotransport reveals that even 1 QL Bi ₂ Te ₃ is sufficient to switch the intrinsic antiferromagnetic coupling in 2 SL MnBi ₂ Te ₄ to ferromagnetic, evidenced by Hall hysteresis and the absence of spin‐flop transitions. Increasing n leads to a monotonic decrease in coercivity and Curie temperature, reflecting progressively weaker interlayer coupling, with a simultaneous enhancement in anomalous Hall response at n = 4. These results demonstrate reversible control of spin configuration by magnetic field and confirm the role of magnetic proximity‐induced exchange coupling in determining the interlayer magnetic ground state, highlighting this atomic‐scale spacer‐engineered heterostructure as a compelling platform for spintronic applications and tunable symmetry‐broken topological quantum phases.