Magnetic states in a triangular antiferromagnet – a model for CoNb₃S₆

CoNb₃S₆ (CNS) is an antiferromagnet (AFM) with triangular planes of Co intercalated with NbS₂ planes. The crystallographic unit cell breaks inversion symmetry, which allows for a Dzyaloshinskii-Moriya interaction. It was recently shown [1, 2] that CNS exhibits a large anomalous Hall effect (AHE) and a very small uniform magnetic out-of-plane moment below the Neel temperature; the magnetic susceptibility was also found to be very small, both in-plane and out-of-plane. The magnetic structure cannot be that of a collinear AFM because a collinear AFM with a small out-of-plane moment cannot yield a large AHE. We used finite-temperature atomistic modeling as well as a reduced 2D model to study the zero-temperature phase diagram. Increasing in-plane next-nearest neighbor interactions leads, together with a biquadratic interaction, to a transition from a single-wavevector spin spiral to a non-collinear AFM. While the former cannot yield a nonzero AHE, the latter does, and this is confirmed by first-principle calculations [3]. We will discuss our model and results in the context of experimental and first-principle electronic structure calculations.

[1] N. Ghimire et al, Nature Comm. 9, 1 (2018).

[2] G. Tenasini et al., Phys. Rev. Research 2, 023051 (2020)

[3] H.  Park, O. Heinonen, and I. Martin, arXiv:2110:03029