Interface-induced 2D ferromagnetism in Fe₃GeTe₂/Bi₂Te₃ heterostructures studied via the circular photogalvanic effect

Two-dimensional van der Waals ferromagnetic materials hold broad prospects in spintronics due to their unique physical properties. Interface engineering is an effective method to tune the magnetic properties of van der Waals magnets and their heterostructures. In this study, the circular photogalvanic effect (CPGE) in Fe₃GeTe₂ (1, 2, 4, 6 nm)/Bi₂Te₃ (8 nm) heterostructures was systematically investigated to reveal the relationship between the interface coupling and the high-temperature ferromagnetism. While both the top Fe₃GeTe₂/Bi₂Te₃ interface and the Bi₂Te₃ bottom surface may contribute to the observed CPGE current, the former was confirmed to be the dominant driver for a Fe₃GeTe₂ thickness larger than 2 nm. A significant spin–orbit coupling effect was found to be present at the Fe₃GeTe₂/Bi₂Te₃ interface and it plays a substantial role in defining the CPGE current. By combining magnetotransport and CPGE measurements, we identified interfacial exchange coupling as the key mechanism for the enhanced Curie temperature (T_C) in FGT/BT heterostructures relative to pure FGT of equivalent thickness. This work highlights the importance of interfacial interactions in tuning physical properties of van der Waals magnet/topological insulator heterostructures, with CPGE serving as a sensitive probe of these effects, and paves the way for utilizing such interactions in magnetic and topological state control.