Elastic properties of the vanadate spinel MnV$_{2}$O$_{4}$

Spinel vanadates AV$_{2}$O$_{4}$ are known to undergo a cubic-to-tetragonal structural phase transition (SPT) at temperature T$_{S}$ and order magnetically at lower temperature T$_{N}$. ZnV$_{2}$O$_{4}$ is characteristic of the entire series and has received extensive theoretical attention. When Mn occupies the A site there is an additional superexchange interaction between Mn and V. This superexchange interaction leads to ferrimagnetic order at about 56 K, involving a ferromagnetic configuration of the V spins. The current work focuses on the elastic properties of MnV$_{2}$O$_{4}$. Resonant Ultrasound Spectroscopy (RUS) has been used to measure the elastic response of the sample, as a function of temperature (5-300K) and magnetic field (0-7 Tesla). The temperature dependence of the frequencies is found to be quite unusual, displaying a softening over a large temperature range. Measurements in magnetic field reveal an additional feature near 50 K, which could represent a striking manifestation of direct spin-orbital coupling.