Defect Structure Guided Room Temperature Ferromagnetism of Y-Doped CeO2 Nanoparticles

In this study, the defect structure of Y doped CeO2 nanoparticles (NPs) was investigated systematically by using spectroscopy and microscopy. The doping level of Y ranges from 0% to 15%. It is demonstrated that Y3+ substitutes Ce and governs the formation of oxygen vacancy. At low doping level, Y3+ randomly distributed throughout the particle. However, as doping level increased above 9%, Y3+ aggregates at the surface and forms Y-rich clusters. Room temperature ferromagnetism (FM) was observed in these Y-doped CeO2 NPs. It is found that the value of saturation magnetization (Ms) increases until Y reaches 9%, then it decreases. Raman, X-ray absorption near edge spectroscopy and X-ray magnetic circular dichroism (XMCD) analysis has provided several aspects on the electronic properties of theses nanoparticles. A charge delocalization occurs upon Y doping on the Ce(Y)-O(VO)-Ce(Y) orbitals. The magnetism is evidenced by XMCD spectroscopy only on Ce orbitals, and the magnetism intensity is mainly related to the amount of Ce3+ at the surface. These features plead for the presence of a defect band at the surface, related to the Ce3+Y interaction, as the origin of the ferromagnetism.