Fe5-xGeTe2 is a centrosymmetric, layered van der Waals (vdW) ferromagnet that displays Curie temperatures Tc (270-330 K) that are within the useful range for spintronic applications.However, little is known about the interplay between its topological spin textures (e.g., merons, skyrmions) with technologically relevant transport properties such as the topological Hall effect (THE), or topological thermal transport. Here, we show via high-resolution Lorentz transmission electron microscopy that merons and anti-meron pairs coexist with Néel skyrmions in Fe5-xGeTe2 over a wide range of temperatures and probe their effects on thermal and electrical transport. We detect a THE, even at room T, that senses merons at higher T's as well as their coexistence with skyrmions as T is lowered indicating an on-demand thermally driven formation of either type of spin texture. Remarkably, we also observe an unconventional THE in absence of Lorentz force and attribute it to the interaction between charge carriers and magnetic field-induced chiral spin textures. Our results expose Fe5-xGeTe2 as a promising candidate for the development of applications in skyrmionics/meronics due to the interplay between distinct but coexisting topological magnetic textures and unconventional transport of charge/heat carriers.

The anomalous Hall, Nernst, and thermal Hall coefficients of the itinerant ferromagnet Fe 3−x GeTe 2 display anomalies upon cooling that are consistent with a topological transition that could induce deviations with respect to the Wiedemann-Franz (WF) law. This law has not yet been validated for the anomalous transport variables, with recent experimental studies yielding material-dependent results. Nevertheless, the anomalous Hall and thermal Hall coefficients of Fe 3−x GeTe 2 are found, within our experimental accuracy, to satisfy the WF law for magnetic-fields µ 0 H applied along its c-axis. Remarkably, large anomalous transport is also observed for µ 0 H a-axis with the field aligned along the gradient of the chemical potential generated by thermal gradients or electrical currents, a configuration that should not lead to their observation. These anomalous planar quantities are found to not scale with the component of the planar magnetization (M ), showing instead a sharp decrease beyond µ 0 H = 4 T or the field required to align the magnetic moments along µ 0 H . We argue that chiral spin structures associated with Bloch domain walls lead to a field dependent spin-chirality that produces a novel type of topological transport in the absence of interaction between the magnetic field and electrical or thermal currents. Locally chiral spin-structures are captured by our Monte-Carlo simulations incorporating small Dzyaloshinskii-Moriya and biquadratic exchange interactions. These observations reveal not only a new way to detect and expose topological excitations, but also a new configuration for heat conversion that expands the current technological horizon for thermoelectric energy applications.

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