Magnetism of the Single Crystal Mg-V-O Spinel

Abstract

In MgV2O4 with normal spinel structure (AB2O4), 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 Mg1+xV2−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 (Mg1−xVx)(V2−xMgx)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.