Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials CoTa₃S₆ and CoNb₃S₆

Recent theoretical studies predicted that non-coplanar antiferromagnetic (AFM) order with scalar spin chirality can often induce large spontaneous Hall effect even without net magnetization or external magnetic field. This phenomenon, i.e. spontaneous topological Hall effect, can potentially be used for the efficient electrical readout of the AFM states, but its experimental verification has long been elusive due to the lack of appropriate materials hosting such exotic magnetism. Here, we report the discovery of all-in-all-out type non-coplanar AFM order in triangular lattice compounds CoM₃S₆ (M = Nb, Ta), by performing the detailed magnetic structure analysis based on polarized neutron scattering experiments and DFT calculations. These compounds are reported to host unconventionally large spontaneous Hall effect despite their vanishingly small net magnetization, and our analysis revealed that it can be well explained in terms of topological Hall effect, which originates from the fictitious magnetic field associated with scalar spin chirality in non-coplanar AFM orders. The present results indicate that the scalar spin chirality mechanism can offer a promising route to realize giant spontaneous Hall response even in compensated antiferromagnets, and highlight intercalated van der Waals magnets as an unique quasi-two-dimensional material platform to enable various nontrivial manner of electrical reading/writing of non-coplanar AFM domains.