Symmetries of modes in Ni3V2O8: Polarized Raman spectroscopy and ab initio phonon calculations

Knowledge of symmetries of vibrational modes is essential for understanding the mechanism of structural transitions and spin-phonon coupling in multiferroics where phonons play a vital role. Using polarized Raman spectroscopy, we have identified and assigned symmetries of 30 out of the 36 expected Raman active modes in Ni3V2O8. The zone-centred phonon mode wavenumbers are calculated using ab initio calculations. The gerade mode wavenumbers are compared with our polarized Raman data whereas ungerade mode wavenumbers are compared with the reported infrared measurements and a good agreement was observed between the experimentally measured wavenumbers and the calculated wavenumbers. The displacements of different types of vibrations calculated and visualized using ab initio phonon calculation are presented. These assignments will be useful for visualization of Raman modes that may be sensitive to different magnetic states and to explore spin-lattice coupling across magnetic transitions.