Thickness tunable zoology of magnetic spin textures observed in Fe₅GeTe₂

Two-dimensional van der Waals (vdW) materials offer avenues to modulate structure and magnetic interactions. In this context, Fe₅GeTe₂ (FGT5), a ferromagnetic compound, stands out. Using a laboratory x-ray source, we reveal the predominant (1×1) FGT5 phase, previously assumed centrosymmetric, lacks inversion symmetry. We also identify a minority phase with a (√3×√3)-R30° superstructure, distinctively two-dimensional, originating from ordered Te-vacancies in the top FGT5 layers.

Real-space magnetic imaging showcases three magnetic states in FGT5 lamellae, varying with thickness: a multi-domain state, a stripe phase, and an uncharted fractal state. The stripe phase houses unconventional type-I and type-II bubbles with non-uniform core spin textures. In thicker FGT5 (~170 µm), a magnetic field induces a 'bobber' or 'cocoon' spin texture stemming from the fractal state.

FGT5's varied magnetic phases make it a captivating subject in the study of 2D vdW magnetic interactions.