Thickness-Dependent Skyrmion Evolution in Fe3GeTe2 During Magnetization Reversal

The van der Waals (vdW) ferromagnet Fe3−xGeTe2 (FGT) offers a versatileplatform for studying 2D magnetism and for potential spintronic applications,owing to its relatively high Curie temperature (200 K to 230 K) andstrong perpendicular magnetic anisotropy. Although some efforts at skyrmioncontrol in FGT have been reported, the details of domain behavior duringmagnetization reversal remain largely unexplored. Here, in situ cryo-Lorentztransmission electron microscopy (LTEM) is used to image the magneticdomain behavior during the field-driven reversal in a single exfoliated FGT flakewith stepped thicknesses. The field-cooling conditions are varied to establishthe initial domain state, and the evolution of stripe domains, skyrmions, anda faceted, patch-like domain phase formed by 360° domain walls is directlyobserved. These transitions show a strong dependence on thickness, andnaturally occurring step edges between thickness regions act as strong pinningsites. Micromagnetic simulations reproduce the experimental behavior andreveal the role of sample thickness, magnetic anisotropy, and applied field onthe resulting domain behavior. This systematic study demonstrates efficientcontrol of skyrmion size, density, and transitions to novel domain structures,offering more precise mechanisms for tailoring topological spin textures.