Magnetism of the single crystal Mg-V-O spinel

In MgV₂O₄ with normal spinel structure (AB ₂O₄), there is magnetic frustration of V³⁺ (3d²⁺) ions located on B-sites, if an antiferromagnetic interaction among B-site spins is essential for its magnetism. The excess Mg substituted materials such as Mg_1+xV_2-xO₄, may construct isolated magnetic triangular lattices, because some of B-sites forming magnetic tetrahedral lattice are substituted by non-magnetic Mg ions, while the normal spinel MgV₂O₄ contains tetrahedral magnetic ion networks. Here, we have succeeded in growing single crystals of Mg-V-O system spinel oxide by conventional floating-zone method. The valence numbers and abundance ratio of V ions in the single crystal were estimated by wavelength-dispersive X-ray fluorescence analysis and X-ray photoelectron spectroscopy analysis. Although the composition ratio was Mg:V 1:2, a small amount of Mg and V ion partly replace each other between A- and B- sites in this crystal. The composition formula is described as (Mg_1-xV_x)(V_2-xMg _x)O₄. The single crystal shows magnetic transition at around 12 K and large negative antiferromagnetic Weiss temperature about -840 K, and the frustration parameter f 70 estimated by those temperatures. This result suggests the existence of strong magnetic frustration in our material.