Structural and spectroscopic properties of the polar antiferromagnet Ni2MnTeO6

We present a structural and spectroscopic study of the compound $\mathrm{N}{\mathrm{i}}_{2}\mathrm{MnTe}{\mathrm{O}}_{6}$, closely related to the polar antiferromagnet $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Te}{\mathrm{O}}_{6}$ known to show a colossal magnetoelectric effect and pronounced elementary magnetoelectric excitations. We prepared single crystals and polycrystalline samples of $\mathrm{N}{\mathrm{i}}_{2}\mathrm{MnTe}{\mathrm{O}}_{6}$ showing the same polar structure as $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Te}{\mathrm{O}}_{6}$ from room temperature down to 4 K with the $R3$ space-group symmetry. Magnetic and dielectric measurements have indicated an antiferromagnetic phase transition at ${T}_{\mathrm{N}}\ensuremath{\approx}70\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, almost 20 K higher than that of $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Te}{\mathrm{O}}_{6}$. Extensive infrared, Raman, and terahertz spectroscopy experiments were employed for investigating lattice and spin excitations, revealing all phonons predicted by the factor group analysis. Terahertz spectra below ${T}_{\mathrm{N}}$ reveal one new excitation, which is strongly influenced by external magnetic field, thus assigned to a magnon.