Magnetic Excitations in MnV$_{2}$O$_{4}$ Studied by Inelastic Neutron Scattering

We focus on the dynamical structure of a spin-orbital coupled system MnV$_{2}$O$_{4}$, which crystallizes in the spinel structure. Each V$^{3+}$ ion with the 3d$^{2}$ configuration is surrounded by an oxygen octahedron. The orbital degree of freedom consequently exists in the t$_{\mathrm{2g}}$ states. Below T$_{\mathrm{oo}}=$53K, the t$_{\mathrm{2g}}$ orbitals are arranged in the layered antiferroic way. Simultaneously, non-collinear ferrimagnetic ordering takes place. In this spin-orbital correlated system, in addition to conventional spin waves, orbital waves and spin-orbital coupled excitations are expected to appear. A measurement of inelastic neutron scattering on single crystals of MnV$_{2}$O$_{4}$ was carried out at 5K using a Fermi-chopper type spectrometer 4SEASONS installed at BL01, J-PARC, Japan. The dispersion of the magnetic excitations at 8-9meV have been revealed, which was only rather vaguely observed in the previous study. We have performed spin-wave calculations based on the spin Hamiltonian and compared with the experimental results in order to identify the 8-9meV modes.