Tailoring Optical Properties via Ru Doping and Magnetic Properties via Ce Doping in α-Fe2−4xZ3xO3 (Z = Ce, Ru) Solid-Solution Nanoparticles

α-Fe2−4xZ3xO3 (Z = Ce, Ru) nanoparticles were synthesized via a conventional solid-state reaction route. X-Ray diffraction analysis confirmed that all compositions crystallize in the single-phase hexagonal hematite (α-Fe2O3) structure, with no detectable secondary phases. Cerium substitution resulted in a pronounced reduction in crystallite size accompanied by a progressive narrowing of the optical band gap, which decreased to approximately 1.73 eV at higher Ce contents. The optical properties were further investigated through absorption coefficient, optical transmittance, and complex refractive index analyses, revealing that cerium-doped hematite exhibits enhanced light-harvesting capability, highlighting its strong potential for optoelectronic and solar-energy conversion applications. Magnetic hysteresis measurements on α-Fe2−4xRu3xO3 samples showed a systematic increase in both coercive field (Hc) and remanent magnetization (Mr) with increasing Ru concentration. This magnetic hardening behavior is attributed to strengthened magnetocrystalline and shape anisotropy induced by Ru incorporation into the hematite lattice. Mössbauer spectroscopy confirmed the presence of Fe3+ and Ru4+ species, providing valuable insight into the oxidation states and local magnetic environments within the corundum-type structure.