# Ferromagnetic Interlayer Exchange Coupling in Magnetic Topological Insulator Sandwich Heterostructures

## TL;DR

Inserting a thin Bi2Te3 layer between MnBi2Te4 layers changes their magnetic coupling from antiferromagnetic to ferromagnetic, offering a tunable platform for spintronics and topological quantum phases.

## Contribution

Demonstrates that a single quintuple layer of Bi2Te3 can switch interlayer coupling to ferromagnetic in MnBi2Te4 heterostructures.

## Key findings

- A single quintuple layer of Bi2Te3 is sufficient to switch antiferromagnetic coupling to ferromagnetic.
- Increasing Bi2Te3 thickness reduces coercivity and Curie temperature, indicating weaker interlayer coupling.
- Enhanced anomalous Hall response is observed at four quintuple layers of Bi2Te3.

## Abstract

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.

A thin topological insulator (Bi2Te3) inserted between two single magnetic septuple layers of MnBi2Te4 is shown to convert the intrinsic antiferromagnetic interlayer coupling into robust ferromagnetism. As the Bi2Te3 spacer thickness increases from 1 to 4 quintuple layers, the weakening coercivity, Curie temperature, and interlayer coupling reveal tuneable magnetic interactions and offer a pathway toward higher‐temperature quantum anomalous Hall states.