Large Magnetodielectric Effect in Composites of Eu ₂ O ₃ Nanoparticles and Mesoporous Silica

Eu ₂ O ₃ nanoparticles were grown within the nanochannels of KIT‐6 mesoporous silica by the impregnation method. The crystallinity and morphology of the samples were investigated by transmission electron microscope (TEM), while phase purity, surface chemistry, and specific surface area were analyzed using XRD, X‐ray photoelectron spectroscopy (XPS), and BET techniques, respectively. DC electrical resistivity of the composite was controlled by the nanoparticles whose conductivity arose due to a small polaron hopping mechanism between Eu ²⁺ and Eu ³⁺ sites. The composites showed a large magnetodielectric effect, having values in the range of 13.6% to 50% depending on the frequency of measurement. The magnetodielectric (M.D.) parameter decreased as the magnetic field was increased. The experimental data were satisfactorily fitted to Catalan's model. A space charge polarization at the interfaces between the amorphous silica and Eu ₂ O ₃ nanophase caused the appearance of dielectric permittivity. The lowering of M.D. with increased magnetic field was the result of positive magnetoresistance of the Eu ₂ O ₃ nanophase, which is ascribed to Zeeman splitting of the localized states contributing to conductivity by electron hopping between them. Magnetic measurements indicate weak antiferromagnetism with a Néel temperature of ∼35.6 K, attributed to oxygen vacancy‐mediated bound magnetic polaron formation. These Eu ₂ O ₃ nanoparticles provide multifunctional building blocks for Re‐based spintronic nanodevices.