Resonant Raman Spectroscopy of the Chiral Antiferromagnet CoNb3S6

We report the first full Raman characterization of the chiral antiferromagnet CoNb3S6; i.e. cobalt-doped NbS2. CoNb3S6 exhibits a large c-axis anomalous Hall effect (AHE) not entirely attributable to the small intrinsic ferromagnetic component (Co) along the c-axis [1]. This interesting behavior suggests that the enhancement in AHE may be because of a combination of magnetic field in the presence of the near-Fermi energy Weyl nodes as predicted [2]. Neutron scattering experiments show incommensurate peaks; however, it was not clear whether the peaks are due to a spin spiral or a spin density wave. Magneto-Raman spectroscopy represents an optimal method to differentiate these structures. Wavelength- and polarized-dependent Raman spectra were collected at room temperature from CoNb3S6 flakes. DFT calculations of modes and band structure were performed and compared to experimental results. Experiments of temperature- and magnetic field-dependent Raman spectroscopy to seek magnon (spin wave) signatures detected no change in the spectral weight below the Neel temperature implying absence of spin density waves, thereby identifying the magnetic structure as helical.

(1) N. Ghimire et al., Nature Commun. Vol. 9, 3280 (2018)
(2) Z. Raines et al., Phys. Rev. B Vol. 96, p. 161115(R) (2017)