G. Zolnierkiewicz

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 Θ=−111(1)K, while a transition to a spin-glass-like state is observed at T≈8.5K, 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<80K, 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 mag...

The preparation and EPR study of nanocrystalline ZnFe2O4

Nanocrystalline zinc oxide doped with different concentrations of Fe2O3(from 5 to 50 wt.%) has been prepared by means of coprecipitation and calcination processes. Depending on the chemical composition, phases of hexagonal ZnO, and/or cubic ZnFe2O4 were identified. The mean crystallite size of the latter phase, determined using the Scherrers formula, varied from 8 to 12 nm. The EPR spectra for six different concentrations of Fe2O3 were recorded. A symmetrical, very intense and broad EPR resonance line has been obtained for the all the samples where the intensity strongly depended on the ratio of ZnO/Fe2O3 in the samples. The resonance field slightly shifted in the direction of lower magnetic field and the integrated intensities increased with increasing concentration of magnetic nanoparticles of ZnFe2O4, where the linewidth showed an extraordinary behaviour. The dipole-dipole interaction depended essentially on the concentration of magnetic nanoparticles.