Generalized Low-Temperature Synthesis of Nanocrystalline Rare-Earth Orthoferrites LnFeO3 (Ln = La, Pr, Nd, Sm, Eu, Gd)

Abstract

Rare-earth orthoferrite LnFeO3 nanocrystals were traditionally synthesized at temperatures higher than 700 °C. In this study, we developed a general nanosized heterobimetallic precursors approach for the synthesis of nanocrystalline rare-earth orthoferrite LnFeO3 (Ln = La, Pr, Nd, Sm, Eu, Gd) at 500 °C. The nanosized heterobimetallic precursors were obtained via the reaction between the Ln and Fe oleates synthesized from their corresponding metal nitrates and sodium oleate. Subsequently, the calcination of the nanosized heterobimetallic precursors at a relatively low temperature (500 °C) produced nanocrystalline rare-earth orthoferrites. The precursors and products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption, thermal analysis (TGA/DSC), and Fourier transform infrared absorption spectroscopy (FT-IR). On the basis of characterization results, we attributed the low temperature formation of nanocrystalline rare-earth orthoferrites to the reduced diffusion distance between the nanosized heterobimetallic precursors. We thought these heterobimetallic precursors ensured the desirable stoichiometry ratio of the orthoferrite products and avoided the formation of garnet. The magnetization features of the orthoferrites were evaluated at room temperature. The M-H curves revealed that EuFeO3 and GdFeO3 exhibit better weak ferromagnetic behavior, corresponding to the antisymmetric-exchange anisotropy. Our method may be extended to prepare other ternary metal oxides at relatively low temperatures.