Electronic Structure of van der Waals Ferromagnet Fe_5-xGeTe₂ in Correlation with Structurally-Dependent Magnetic Domains

The intrinsic magnetic ordering discovered in two-dimensional (2D) materials offers exciting opportunities for both fundamental understanding of spin states in quantum materials and potential development of new spintronic systems. Particularly, magnetic order has been reported in thin films of various 2D materials down to few-layer van der Waals (vdW) flakes or even monolayers, where the magnetic texture becomes highly dependent on the local structure of the film. One of the major research efforts in this field focuses on the understanding and coherent control of the magnetic patterns through material engineering, for achieving certain magnetic domains on small scales can be highly beneficial for building high-density memory devices. Another research avenue of great interest involves developing systems with near-room-temperature magnetism which can significantly enhance the applicability of the device. Among vdW ferromagnets, Fe_5-xGeTe₂ not only exhibits variable ferromagnetic textures but also a critical temperature close to room temperature even in the form of vdW flakes, making it a promising system for future spintronic applications. However, the underpinning electron behaviors accounting for the exotic magnetic ground states have not been well understood. The challenge lies in the lack of technological solutions that can effectively correlate the magnetic domain patterns with the electronic structure of Fe_5-xGeTe₂. While the bulk properties of Fe_5-xGeTe₂ are relatively better understood, its ferromagnetism and corresponding contributions from orbital magnetic moments in thin film form remain largely unexplored. While the tendency of Fe_5-xGeTe₂ to form stacking faults, namely the only partially occupied Fe(1) position, presumably plays a minor role in the magnetic behaviors in bulk crystals, its impacts can be much more pronounced in exfoliated flakes in deciding the local spin states. Bridging this knowledge gap requires new investigative strategies: In this study, the electronic structure and magnetic domains of Fe_5-xGeTe₂ were investigated simultaneously by X-ray photoemission electron microscopy (X-PEEM) which enables a combination of magnetic imaging, X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). Subsequent density functional theory (DFT) simulation was performed to rationalize the X-PEEM results. The combined experimental and computational approach was able to correlate the electron transitional behaviors with structurally-dependent magnetic order of exfoliated Fe_5-xGeTe₂ thin films, identifying crucial contributions from hybridized orbitals to the formation of specific spin textures as observed by X-PEEM.