Fe5-xGeTe2 is a layered and exfoliable van der Waals (vdW) ferromagnet that displays Curie temperatures Tc ranging between 270 and 330 K, which are within a useful range for spintronic applications. Nevertheless, little is known about the interplay between topological spin textures (e.g., merons, skyrmions) and their transport properties (e.g., the topological Hall effect (THE)) which might influence the response of devices and be harvested for applications. Here, we show through a Lorentz transmission electron microscopy study in Fe5-xGeTe2 the coexistence of merons and anti-meron pairs with Néel skyrmions and antiskyrmions over a broad range of temperatures upon approaching a magneto-structural transition. We measured the THE associated to both types of spin textures finding that it is affected by their coexistence being measureable at room temperature and beyond 1. Remarkably, we also observe a sizeable unconventional THE for currents and magnetic fields aligned along a planar direction, a configuration that is insensitive to the Lorentz force 2. We attribute this to carrier interaction with magnetic field-induced chiral spin textures. Given that the Curie temperature of Fe5-xGeTe2 can be increased via either Ni 3 or Co 4 doping, we conclude that 2D centro-symmetric vdW magnets are ripe for the exploration of their possible applications in skyrmionics/meronics 5 and also of new hybrid spin quasiparticles as well as their possible manipulation via external stimuli such as current and light. Our results suggest that unconventional topological spin textures (that is, those distinct from merons or skyrmions) might exist in atomically thin vdW layers whose properties have yet to be unveiled.

References:

1 Brian W. Casas, Yue Li, Alex Moon et al., Room temperature unconventional topological Hall response in a van der Waals ferromagnet driven by meron-antimeron pairs (unpublished)
2 Juan Macy, Danilo Ratkovski, Purnima P. Balakrishnan et al., Magnetic field-induced non-trivial electronic topology in Fe3−xGeTe2, Appl. Phys. Rev. 8, 041401 (2021).
3 Xiang Chen, Yu-Tsun Shao, Rui Chen et al., Pervasive beyond Room-Temperature Ferromagnetism in a Doped van der Waals Magnet, Phys. Rev. Lett. 128, 217203 (2022).
4 Hongrui Zhang, David Raftrey, Ying-Ting Chan et al., Room-temperature skyrmion lattice in a layered magnet (Fe0.5Co0.5)5GeTe2, Sci. Adv.8, eabm7103 (2022).
5 Hamed Vakili, Jun-Wen Xu, Wei Zhou et al., Skyrmionics—Computing and memory technologies based on topological excitations in magnets, J. Appl. Phys. 130, 070908 (2021).