Lattice and magnetic dynamics in the polar, chiral, and incommensurate antiferromagnet Ni2InSbO6

Complex systems with coexisting polarity, chirality, and incommensurate magnetism are of great interest because they open new degrees of freedom in the interaction between crystal and magnetic subsystems and therefore they host a plethora of intriguing physical properties. Here we report the optical properties and lattice and spin dynamics of ${\mathrm{Ni}}₂{\mathrm{InSbO}}₆$ single crystals. This material was studied with the use of polarized optical microscopy and micro-Raman spectroscopy in the temperature range 10--300 K. ${\mathrm{Ni}}₂{\mathrm{InSbO}}₆$ crystallizes in a polar structure described by the noncentrosymmetric space group $R3$ and the two types of structural domains were visualized due to the natural optical activity of opposite chirality. Raman tensor elements of most $A$ and $E$ phonons along with their symmetry were determined. The manifestation of LO-TO splitting was observed for the $A$ modes. By tracking the temperature dependencies of phonon frequencies, the well pronounced spin-phonon interaction was observed for several modes below and above the N\'eel transition temperature ${T}_N =76\phantom{\rule{4pt}{0ex}}\mathrm{K}$. In the antiferromagnetic phase, a broad excitation centered at $247\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, was detected and assigned to the two-magnon mode and this value was used for estimating exchange parameters through linear spin-wave theory calculations.