Bound magnetic polarons, phonon confinement and charge transfer effects in Cr2O3/SiO2 composites

Cr₂O₃/SiO₂ composites with varying Cr₂O₃ content (10 %, 30 %, and 50 %) were synthesized and systematically analyzed for their structural, vibrational, chemical, and magnetic properties. X-ray diffraction (XRD) confirmed the successful incorporation of Cr₂O₃ into the SiO₂ matrix, with a gradual increase in Cr₂O₃ phase fraction and a minor shrinkage in lattice volume, indicative of strong interparticle interactions. Raman spectra exhibited a systematic redshift and peak broadening in the characteristic Cr₂O₃ mode, indicative of interfacial strain and phonon confinement, while Raman mapping revealed phase clustering at higher Cr₂O₃ content. X-ray photoelectron spectroscopy (XPS) identified a higher Cr⁶⁺ fraction at increased Cr₂O₃:SiO₂ fractions, indicating enhanced Cr-O-Si interactions. Magnetic measurements at 50 K and 300 K demonstrated dominant antiferromagnetic behavior alongside weak ferromagnetic contributions, attributed to defect-induced bound magnetic polarons (BMPs). BMP density increased with Cr₂O₃ content, highlighting localized spin interactions at the Cr₂O₃/SiO₂ interface. These findings elucidate the interplay of structural stability, charge transfer, and defect-mediated magnetism, offering insights for optimizing Cr₂O₃/SiO₂ composites in spintronic, magneto-optical, and catalytic applications.