Electronic Structures and Magnetic Transitions via Layer Control in Two-Dimensional Ferromagnetic van der Waals Films*

Fe₃GeTe₂ (FGT) has attracted significant attention due to its intriguing properties, notably its two-dimensional (2D) itinerant magnetism, and correlated behavior. Experimental studies have verified that the Curie temperature (T_C) of FGT can be tuned by adjusting the layer number and carrier concentration. Our current empirical understanding of these phenomena, particularly in the monolayer and multilayer regime, is still limited. In this study, we employed molecular beam epitaxy (MBE) to grow high-quality stoichiometric FGT films with precise layer control, down to the monolayer limit. By employing angle-resolved photoemission spectroscopy (ARPES), we observed distinct evolution in the band structure from monolayer to bilayer systems, which are corroborated by density function theory calculations. Additionally, we investigate the evolution of carrier density with respect to both sample thickness and temperature. Through a detailed comparison with theoretical calculations, we established a direct link between band structures, carrier concentrations, and the ferromagnetic phase transitions, highlighting the influence of exchange coupling between localized and itinerant carriers. Our research offers valuable insights into the fundamental properties of this 2D van der Waals ferromagnetic material and motivates investigation of coupling mechanisms between localized and itinerant carriers in the field of 2D van der Waals ferromagnetic materials.