Neutron Scattering Study of Magnetic and Orbital Order in MnV$_{2}$O$_{4}$

Neutron diffraction and inelastic scattering has been used to study the spinel system MnV$_{2}$O$_{4}$. The results confirm the existence of two phase transitions. The first, near 56 K, is from a paramagnetic state to a collinear ferrimagnetic phase. There is a second simultaneous structural and magnetic transition at 53 K to a tetragonal structure with a non-collinear ferrimagnetic state. The low T magnetic structure has been definitively resolved, and is seen to be associated with a gap in the magnetic excitation spectrum. The magnetic structure is compatible with a staggered orbital ordering.Inelastic scattering has been carried out using both triple axis and time of flight techniques, and several branches of magnetic excitations are visible. These observations put tight constraints on theoretical models for MnV$_{2}$O$_{4}$. An initial account of some of the results of this work appears in arXiv:0711.1844v1.