Defect Structure Guided Room Temperature Ferromagnetism of Y‑Doped CeO<sub>2</sub> Nanoparticles
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Abstract
In
this study, the defect structure of Y doped CeO<sub>2</sub> nanoparticles
(NPs) was investigated systematically by using spectroscopy and microscopy.
The doping level of Y ranges from 0% to 15%. It is demonstrated that
Y<sup>3+</sup> substitutes Ce and governs the formation of oxygen
vacancy. At low doping level, Y<sup>3+</sup> randomly distributed
throughout the particle. However, as doping level increased above
9%, Y<sup>3+</sup> aggregates at the surface and forms Y-rich clusters.
Room temperature ferromagnetism (FM) was observed in these Y-doped
CeO<sub>2</sub> NPs. It is found that the value of saturation magnetization
(M<sub>s</sub>) 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(V<sub>O</sub>)-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 Ce<sup>3+</sup> at the
surface. These features plead for the presence of a defect band at
the surface, related to the Ce<sup>3+</sup>–Y interaction,
as the origin of the ferromagnetism