Structural, magnetic and 151Eu Mössbauer studies of mechanosynthesized nanocrystalline EuCr1−xFexO3 particles

Abstract

We report on the mechanosynthesis of single-phased EuCr1−xFexO3 (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) nanocrystalline particles (∼20–50nm) at temperatures that are significantly lower than those at which the corresponding bulk materials are conventionally synthesized, and their structural and magnetic characterization. It was found that the average crystallite size decreased, the lattice parameters increased and the unit cell gets more distorted with increasing x. All samples showed weak ferromagnetism due to spin canting. Although Curie temperatures increase with increasing x, they are significantly lower than those of the corresponding bulk materials. Simple Curie–Weiss fits for the paramagnetic susceptibilities were found to be more physically plausible relative to fits where Vleck-type contributions to the paramagnetic susceptibilities due to Eu3+ ionic sublattices, which are separate from of the Cr3+/Fe3+ ones, were assumed. The non-existence of such separate Eu3+ and Cr3+/Fe3+ sublattices was further supported by 151Eu Mössbauer spectra of the nanoparticles which favor a non-equilibrium cation distribution wherein a considerable amount of Eu3+ and Cr3+/Fe3+ ions exchange their normal dodecahedral and octahedral perovskite-related sites, respectively. The supertransferred hyperfine magnetic field at the site of the 151Eu nuclei, induced by neighboring Cr3+/Fe3+ ions, was found to be considerably larger for B-site nuclei than for A-site ones. The antisite behavior concluded in this study is consistent with 57Fe Mössbauer spectral analysis of the nanoparticles that favor the presence of the majority of the Fe3+ ions at the usual B-sites and minority Fe3+ ions either at the A-sites or at B-sites with Eu3+/Cr3+ nearest B-site neighbors. The relative site occupancies associated with the cationic site exchange inferred from both the 151Eu and 57Fe Mössbauer spectra are remarkably consistent.