Site-Ordering/Disordering-Induced Magnetic Textures in a vdW Ferromagnet via Engineered Inversion-Symmetry Breaking

Fe_5-xGeTe₂ single crystals exhibit nonquenched (NQ) and quench-cooled (QC) phases with distinct magnetic properties, but their structure-dependent magnetic behaviors remain insufficiently understood in real space. Here, we combine cryogenic magnetic force microscopy and scanning tunneling microscopy to correlate magnetic domain evolution with local structural characteristics. Thermal history controls the disorder/order of Fe(1) sites, leading to global inversion symmetry in the NQ phase and broken inversion symmetry in the QC phase. During spin reorientation, the NQ phase undergoes a branching-to-labyrinthine domain transition and stabilizes distinct 3D spin textures through magnetic dipolar interactions, resulting in a more robust global magnetic state. In contrast, the QC phase shows enhanced perpendicular magnetic anisotropy and exchange coupling, giving rise to a higher Curie temperature. The broken inversion symmetry gives rise to Dzyaloshinskii-Moriya interaction, whose spatial distribution is further fragmented by structural domains. This combined effect promotes localized magnetic states, suppresses domain transformation during spin reorientation, and yields irregular field-induced domain patterns. These results clarify the microscopic mechanisms underlying the contrasting magnetic behaviors of Fe_5-xGeTe₂ and provide guidance for its spintronic applications.