Effect of Co³⁺ substitution on the structural, optical, and room-temperature magnetic properties of SnO₂ nanoparticulates

To investigate the contribution of cobalt in initiating room-temperature ferromagnetism in SnO₂ nanocrystals, the structural, optical, and magnetic behaviors of Co-doped SnO₂ nanoparticulates with different dopant concentrations were examined. The structures of the samples were confirmed to be tetragonal and the shift in diffraction peaks as well as reductions in lattice parameters confirmed the incorporation of Co³⁺ ions into the SnO₂ lattice. The diffuse reflectance spectroscopy data reveal the augmentation of absorption to upper wavelength and a decrease in energy bandgap was also observed. Co-doped samples revealed room-temperature ferromagnetism with a small contribution of paramagnetic ordering, which disappears with increase in dopant concentration. An increase in the Co content leads to a rapid increase in the saturation magnetization of the system whereas the coercivity seems to be almost constant for all the Co-doped SnO₂ nanoparticles. The ferromagnetic properties of the synthesized samples depend on the distribution of defects, nanometric size, as well as the surface diffusion of Co ions on the tin oxide nanoparticles.