and Their Heterostructures with Topological Insulators*

As a 2D van der Waals material, Fe₃GeTe₂ (FGT) stands out because of its strong perpendicular magnetic anisotropy and high Curie temperature (T_C). A lot of interesting phenomena have been studied in FGT thin films and heterostructures, such as skyrmions and room temperature ferromagnetism. However, most studies are based on exfoliated FGT. Here, we ultilize molecular beam epitaxy for high-quality epitaxial monolayer and multilayer FGT. Cross-sectional transmission electron microscopy (TEM) shows an atomically-sharp interface between the FGT film and Ge(111) substrate. We also developed heterostructures with topological insulators such as FGT/Bi₂Te₃ and FGT/SnTe which are very interesting for spin-orbit torque and magnetic topological states. Magneto-optic Kerr Effect (MOKE) and Anomalous Hall Effect (AHE) were used to confirm square hysteresis loops and MOKE microscopy made it possible for us to catch a glimpse of its domain structure during magnetization switching. By doing MOKE measurements on both FGT/Ge and FGT/Bi₂Te₃, we observed an enhancement of T_C in the FGT/Bi₂Te₃ system. Finally, we utilized MOKE to probe the few-layer limit to determine the layer dependence of FGT films on Bi₂Te₃.