Cobalt doping induced emergent humps of Hall resistance in van der Waals ferromagnetic nanodevices of (Fe0.74Co0.26)3GeTe2

As a promising van der Waals (vdW) magnet, Fe3GeTe2 (FGT) has an inversion symmetry in structure, thus nominally prohibiting the generation of the Dzyaloshinskii–Moriya interaction and the resultant topological Hall effect (THE), which is manifested as hump-like features in transport. By virtue of doping, like the method of fabricating heterostructures, the crystal inversion symmetry of FGT could be broken artificially; therefore, humps of Hall resistance due to the THE are expected. However, alternative interpretations indicate inhomogeneity-induced multi-channel anomalous Hall effect (AHE) could also give rise to these humps. Here, besides the magnetic properties modified by Co doping, we report emergent humps in (Fe0.74Co0.26)3GeTe2 (FCGT) nanodevices. By scanning minor loops, partial anomalous Hall loops exceeding the full loop cannot be attributed to the THE, while it is in line with the multi-channel AHE scenario. These channels likely develop as a result of the Co atoms in FGT being randomly distributed, leading to multiple spatially separated magnetic regions with distinct coercive fields and magnetizations. By combing these AHE channels, the hump features in FCGT are effectively reproduced. Our work implies that the underlying multi-channel transport could also facilitate the development of versatile nanodevices utilizing the doped vdW ferromagnets.