Vibrational properties of SrVO2H with large spin-phonon coupling

Abstract

The antiferromagnetic transition metal oxyhydride ${\mathrm{SrVO}}_{2}\mathrm{H}$ is distinguished by its stoichiometric composition and an ordered arrangement of H atoms. The tetragonal structure is related to the cubic perovskite and consists of alternating layers of ${\mathrm{VO}}_{2}$ and SrH. ${d}^{2}$ V(III) attains a sixfold coordination by four O and two H atoms. The latter are arranged in a trans fashion, which produces H--V--H chains along the tetragonal axis. Here, we investigate the vibrational properties of ${\mathrm{SrVO}}_{2}\mathrm{H}$ by inelastic neutron scattering and infrared spectroscopy combined with phonon calculations based on density functional theory. The H-based vibrational modes divide into a degenerate bending motion perpendicular to the H--V--H chain direction and a highly dispersed stretching motion along the H--V--H chain direction. The bending motion, with a vibrational frequency of approximately 800 ${\mathrm{cm}}^{\ensuremath{-}1}$, is split into two components separated by about 50 ${\mathrm{cm}}^{\ensuremath{-}1}$, owing to the doubled unit cell from the antiferromagnetic structure. Interestingly, spin-phonon coupling stiffens the H-based modes by $50\ensuremath{-}100\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ although super-exchange coupling via H is very small. Frequency shifts of the same order of magnitude also occur for V--O modes. It is inferred that ${\mathrm{SrVO}}_{2}\mathrm{H}$ displays the hitherto largest recognized coupling between magnetism and phonons in a material.