English abstract
Single-phased EuCr)-»FeO3 perovskite-related nanocrystalline particles (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized via the prolonged milling of stoichiometric mixtures of Eu2O3, Cr2O3 and a-Fe2O3 followed by sintering. The formation temperatures of the resulting EuCr-/Fe,O3 nanoparticles are ~ 550°C to ~ 800°C lower than those at which the materials are conventionally synthesized. Both the milling time of the initial reactants' mixtures and the formation temperature of the EuCrı-xFe,O3 nanoparticles were found to decrease with increasing Fe content (x). Increasing the x value resulted in decreasing the average crystallite size from ~ 35 nm to ~ 19 nm with concomitant expansion of the unit cell of the resultant EuCr-xFexO3. The nanoparticles, which are generally spherical in shape, were found to cluster with increasing x value. The EuCr/-xFexO3 samples with x < 0.7 were found to be paramagnetic at room temperature, whereas those with x > 0.7 exhibited a weak ferromagnetic behavior and Curie temperatures that increased with increasing x value. The Curie temperature of the nanoparticles with x = 1 (EuFeO3) was found to be ~ 40 K lower than that of larger, conventionally-prepared EuFeO3 particles suggesting that the magnetic anisotropy energy is lowered by virtue of the small size. Mössbauer measurements have shown that only Eu' and Feions are present in the synthesized EuCr-/Fe,O3 samples with no traces for other Eu and Fe oxidation states. In consistency with the abovementioned magnetic properties, the 295K "Eu and "Fe Mössbauer spectra have shown magnetic hyperfine interactions to exist only for the EuCrı-zFe,O3 nanoparticles with x > 0.7. Some superparamagnatic nanoparticles were found to exist in the samples with x = 0.7 and 0.9. Additionally, Mössbauer spectroscopy has shown that the superparamagnetic blocking temperatures as well as the Curie temperatures of all the EuCrı-xFeO3 nanoparticles are higher than 78 K.
