Magnetic frustration in the site ordered Mg3Fe4(VO4)6 vanadate

The magnetic properties of the site ordered multicomponent vanadate Mg3Fe4(VO4)(6) are studied using dc magnetization and electron paramagnetic resonance (EPR) measurements. The static susceptibility shows antiferromagnetic interactions between Fe3+ spins with a Curie-Weiss temperature Theta=-111(1) K, while a transition to a spin-glass-like state is observed at T approximate to 8.5 K, indicating appreciable spin frustration. EPR measurements corroborate the presence of antiferromagnetically coupled Fe3+ spins from high temperatures, while a distinct change in the temperature variation of the EPR parameters is observed at T < 80 K, complying with the mean-field energy scale provided by the Curie-Weiss temperature of the system. The resulting magnetic inhomogeneity that persists despite the absence of cation disorder between magnetic and diamagnetic metal ions is attributed to the presence of small amounts of oxygen deficiency that modifies the connectivity and superexchange coupling between Fe3+ spins and leads to a disordered magnetic ground state. (c) 2007 American Institute of Physics.