Facile hydrothermal synthesis and characterization of novel Co-doped iron oxides nanoparticles with tunable structural, optical, and magnetic properties

Fe[Formula: see text]Co x O nanoparticles ([Formula: see text]−0.20 at.%) were synthesized via a hydrothermal method to systematically investigate the effect of cobalt incorporation on their structural, optical, surface, and magnetic properties. X-ray diffraction confirmed the formation of phase-pure rhombohedral Fe 2 O 3 with no detectable secondary cobalt phases, while progressive peak shifts indicated successful substitution of Co ions into the iron oxide lattice. Cobalt doping led to a controlled increase in crystallite size accompanied by reduced lattice strain and dislocation density, reflecting improved structural ordering. FTIR spectra revealed modifications in metal oxygen bonding consistent with dopant-induced lattice distortion. Morphological analysis showed aggregated near-spherical nanoparticles, with enhanced grain growth at higher cobalt concentrations. Nitrogen adsorption–desorption measurements demonstrated mesoporous characteristics, with a maximum BET surface area of 39.54[Formula: see text]m 2 [Formula: see text]g[Formula: see text] at ([Formula: see text]). X-ray photoelectron spectroscopy identified mixed Fe[Formula: see text]/Fe[Formula: see text] and Co[Formula: see text]/Co[Formula: see text] oxidation states, indicating strong Fe–O–Co interactions and increased surface defect density. Optical studies revealed a systematic blue shift of the absorption edge and a widening of the optical bandgap from 2.57[Formula: see text]eV to 3.23[Formula: see text]eV with increasing cobalt content. Magnetic measurements showed enhanced saturation magnetization and coercivity, reaching 9.1[Formula: see text]emu[Formula: see text]g[Formula: see text] and 275[Formula: see text]Oe at ([Formula: see text]), followed by a decline at higher doping levels due to defect-mediated spin canting. These results demonstrate that controlled cobalt doping enables effective tuning of Fe 2 O 3 nanoparticle properties, highlighting their potential for applications in spintronics, magnetic sensing, and photocatalysis.