Gate-Tunable Anomalous Hall Effect in Van der Waals ferromagnetic insulator–topological insulator heterostructure

The search of novel topological phases like the quantum anomalous Hall insulator has motivated different schemes to introduce magnetism in topological surface states.  One way to achieve this was obtained by the growth of ferromagnetically doped topological insulators (TI), but the dopants added disorder and introduced defects. A different route is by achieving the magnetic proximity effect, in which a ferromagnet is directly in contact with a topological insulator forming a heterostructure. Previously, most of the heterostructures have been assembled via growth techniques that have materials constraints related to chemical diffusion, difference in the growth conditions and lattice mismatch. Here, we show that the magnetic proximity effect can still be obtained in heterostructures assembled via a more generally-applicable dry transfer method, as we demonstrate for exfoliated micrometer-sized thin flakes of van der Waals TI and ferromagnetic materials (BiSbTeSe₂/Cr₂Ge₂Te₆) and evidenced in the observation of an anomalous Hall effect (AHE). We further show that the AHE can be modulated by electrostatic gating as the carrier density in the heterostructure changes.