Crystallographic and magnetic structure of ZnV2O4 -: Structural phase transition due to spin-driven Jahn-Teller distortions

We report on the crystallographic and magnetic structure of the geometrically frustrated spinel ZnV2O4 as determined by neutron powder diffraction. At T = 51 K, a cubic-to-tetragonal phase transition takes place. The low temperature crystallographic structure is characterized by the space group I4(1)/amd and unit cell dimensions a/root2 x a/root2 x a with a being the lattice constant of the cubic phase. The corresponding antiferromagnetic structure of the vanadium sublattice can be described by a propagation vector k = (001) with the magnetic moments being aligned parallel to the c-axis. The ordered magnetic moment is 0.65(5) mu(B) per V3+ ion. The experimental results are in accord with recent theoretical models proposing spin-driven Jahn-Teller distortions. The results are also compared with reports on non-ordering ZnV2O4.