  Controlling magnetic order in magnetic topological insulators (MTIs) is a key
to developing spintronic applications with MTIs, and is commonly achieved by
changing the magnetic doping concentration, which inevitably affects
spin-orbit-coupling strength and the very topological properties. Here, we
demonstrate tunable magnetic properties in topological heterostructures over a
wide range, from a ferromagnetic phase with Curie temperature of around 100 K
all the way to a paramagnetic phase, while keeping the overall chemical
composition the same, by controlling the thickness of non-magnetic spacer
layers between two atomically-thin magnetic layers. This work showcases that
spacer-layer control is a powerful tool to manipulate magneto-topological
functionalities in MTI heterostructures. Furthermore, the interaction between
the MTI and the Cr2O3 buffer layers also led to robust topological Hall effect
surviving up to a record-high 6 T of magnetic field, shedding light on the
critical role of interfacial layers in thin film topological materials.
