Characterization of Sm-doped CeO2 nanoparticles and their magnetic properties

Cubic phase Sm-doped CeO2 nanoparticles (Ce1−xSmxO2, x=0, 0.05, 0.10, 0.15 and 0.20) were synthesized by the polymer pyrolysis method. X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) were employed to characterize the phase, morphology, valence states and magnetic properties of the samples. The samples were calcined at the low temperature of 600 °C which resulted in crystallite sizes of 10–20 nm. Raman and XPS spectra showed the presence of Ce4+, Ce3+ and Sm3+ ions and oxygen vacancies in the samples. Magnetization curves obtained from all samples exhibited ferromagnetic behavior at room temperature (RT-FM) with a maximum value of 0.012 emu/g for x=0.15. The data exhibited a good fit to bound magnetic polaron (BMP) model curves which account for the RT-FM behaviour by having sufficient concentrations of electrons bound to oxygen vacancies to facilitate a long-range exchange interaction between Ce3+ ions. However, the relatively low values obtained for the BMP concentrations suggest that other mechanisms may also be at play.