Iron-based van der Waals (vdW) ferromagnets with relatively high ordering temperatures are a current research focus due to their significance in fundamental physics and potential applications in spintronics. Competing magnetic interactions and anisotropies can give rise to nontrivial spin textures in these materials, resulting in novel topological features. ${\mathrm{Fe}}_4{\mathrm{GeTe}}_2$ (F4GT) is a nearly room-temperature vdW ferromagnet, well known for hosting a spin-reorientation transition (SRT) arising from the competition between perpendicular magnetic anisotropy (PMA) and shape anisotropy. In this work, we investigate the angle-dependent magneto-transport properties of F4GT single crystal nanoflakes. We report a large topological Hall effect (THE) associated with noncoplanar spin textures, persisting over a wide temperature range around SRT in presence of in-plane external magnetic field. Moreover, we find a thickness-sensitive THE signal for the $c$-axis orientation of the magnetic field at a low-temperature regime which is associated with a reentrant Lifshitz transition, suggesting interplay between magnetism and the Fermi surface in F4GT.

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• Hall effect
• Magnetism
• Magnetotransport
• Topological materials
• Ferromagnets
• Transport techniques