Growth and magnetic properties of stoichiometric and site-disordered single crystalline MgV sub(2)O sub(4)

We have grown several single crystals of the highly frustrated S = 1 spinel MgV sub(2)O sub(4) using different starting compositions and growth conditions. From our study of their physical properties by magnetic susceptibility, heat capacity, and single-crystal neutron and powder-diffraction measurements, we observe that a minute amount of disorder suppresses the structural and magnetic phase transitions. As little as 3% disorder in the octahedral site introduced random strain, which was enough to completely suppress the transitions and induce a spin-glass phase at low temperatures. We believe that the reason is spin-exchange disorder rather than disorder in the weakly diluted magnetic lattice. Our results also show that the MgO-V sub(2)O sub(3) system is a solid solution that melts slightly incongruently, and we demonstrate that by using an optimized solvent in the traveling-solvent floating-zone configuration a large single crystal (l = 25 mm, d = 6 mm) with a homogeneous composition, free of site disorders can be grown.