Structural, magnetic and ¹⁵¹Eu Mössbauer studies of mechanosynthesized nanocrystalline EuCr_1-xFe _xO₃ particles

We report on the mechanosynthesis of single-phased EuCr_{1- x}Fe_xO₃ (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) nanocrystalline particles (∼20-50 nm) 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 Cr ³⁺/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.