Magnetic dynamics and spin-phonon coupling in the antiferromagnet Ni2NbBO6

Antiferromagnetic systems with rich spin dynamics and pronounced interplay between magnetic and lattice degrees of freedom are of great interest in the emerging field of terahertz and subterahertz magnonics and spintronics. Here we report on spin and lattice dynamics of single crystals of ${\mathrm{Ni}}_{2}{\mathrm{NbBO}}_{6}$ studied with the use of polarized Raman spectroscopy in the temperature range of 10--300 K which includes the antiferromagnetic transition at ${T}_{N}=23.5$ K. Well-defined and highly polarized magnetic excitations were observed below and partly above ${T}_{N}$. Three magnetic modes at 30, 84, and 113 ${\mathrm{cm}}^{\ensuremath{-}1}$ (at $T=10$ K) were detected. The two high-energy magnetic excitations were identified as two-magnon modes. In total, 57 out of the expected 60 Raman-active phonons were registered and identified. Several modes revealed a nontrivial spin-phonon coupling manifesting either hardening or softening mostly below ${T}_{N}$. The possible magnetic space groups were determined through symmetry analysis. Spin-wave spectra and density of states were calculated within the linear spin-wave theory for supporting the experimental findings.