Synthesis and Characterization of Rare‐Earth Orthoferrite LnFeO₃ Nanoparticles for Bioimaging

A combination of sol–gel synthesis and thermal decomposition was developed for preparing nanosized, perovskite‐type LnFeO 3 (Ln = Eu, Gd, Tb) powders. Perovskite‐type powders with crystalline particles of 100 nm average size, as determined by transmission electron microscopy (TEM), could be obtained after a thermal treatment at 800 °C. The perovskite nanoparticles (NPs) were further characterized by X‐ray powder diffraction and Mössbauer spectroscopy. These were in agreement with the pure perovskite LnFeO 3 structure with the expected Zeeman sextet corresponding to a magnetically ordered phase. Magnetization measurements [ M ( H )] at 5 K and 300 K showed a behavior that is dominated by antiferromagnetic interactions and weak ferromagnetism in EuFeO 3 , while for Ln = Gd, Tb, they were dominated by the low ordering temperature Ln magnetic sublattice. The colloidal aqueous NPs suspensions exhibited no significant leaching of free Ln 3+ ions. Their relaxivities define them as potential T 2 MRI contrast agents for further biomedical applications. The NPs showed fast uptake and no cytotoxicity at concentrations below 62.5 µg/mL with respect to Hela cells.