Ferromagnetic Interlayer Exchange Coupling in Magnetic Topological Insulator Sandwich Heterostructures.

A single septuple layer (SL) of MnBi2Te4 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 Bi2Te3 with quintuple-layer (QL) units. Here, electrical transport measurements are performed on 1 SL MnBi2Te4/n QL Bi2Te3/1 SL MnBi2Te4 sandwich heterostructures (n = 0-4) to investigate the role of Bi2Te3 spacer thickness in tuning interlayer magnetic interactions. Magnetotransport reveals that even 1 QL Bi2Te3 is sufficient to switch the intrinsic antiferromagnetic coupling in 2 SL MnBi2Te4 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.