Oxygen Vacancy Dependent Magnetism of CeO2 Nanoparticles Prepared by Thermal Decomposition Method

This study reports that highly oxygen-deficient CeO2 nanoparticles (NPs) can be obtained without reduction treatment by using thermal decomposition method. Different amounts of surfactants are used to control the size of the NPs. The X-ray absorption near-edge spectra (XANES) indicate that the concentration of Ce3+ is higher than 20% for all NPs. It is also found that most Ce3+ locates at the surface. Magnetic-measurement results show that room-temperature ferromagnetism (FM) of the CeO2 is closely related to the concentration of Ce3+ at the surface (I-s(Ce3+)). Saturation magnetization (M-s) reaches the maximum value with an I-s(Ce3+) of about 40%; however, M-s decreases when I-s(Ce3+) is raised further. The highest M-s in this study is obtained from the sample without surfactant (M-s = 0.12 emu/g). This is comparable with the results in other reports in which the CeO2 NPs were subjected to the reduction treatment. Notably, NPs become paramagnetic when I-s(Ce3+) reaches 48%. This study suggests that oxygen vacancy is essential for the formation of FM in CeO2 NPs. However, FM will be suppressed with excess oxygen deficiency. The effect of surfactant on the growth and the stoichiometry of the CeO2 particles will also be discussed in this report.