Oxygen-exposure mediated electron transfer and d0 ferromagnetism in metal oxide nanocrystals system

Enhanced Room‐Temperature Ferromagnetism in Composite CeO2/CeF3 Nanoparticles

“…Thus magnetization measurements reveal a considerable increase of the paramagnetic contribution due to paramagnetic Ce 3+ ions in the VA sample. This experimental result shows that the vacancies do not necessarily lead to ferromagnetism which is in accordance with earlier publications . However, the origin of ferromagnetism in oxide nanoparticles like ceria is frequently explained by the oxygen vacancies at the surface of nanoparticles.…”

“…A number of experimental works supported by DFT calculations point to defects like oxygen vacancies as the origin of room temperature ferromagnetism . On the contrary, some publications challenge this supposition on the basis of their experimental results . The vacancies forming in pure ceria relate to its ability to change the oxidation state of cerium ions between the Ce 4+ and Ce 3+ valence states, depending on the ambient conditions .…”

Novel Approaches of Nanoceria with Magnetic, Photoluminescent, and Gas-Sensing Properties

“…The influence of temperature on reactions with CO was previously considered by Lv et al The CCCT mechanism can also be expressed after CO exposure, according to these equations, where the electron situated in adsorbed oxygen species onto the surface returns to the system, reducing the cluster from [CeO 7 ·V O • ] to [CeO 7 ·V O × ], with a consequent decrease of the electrical resistance. We can observe that when CO reacts at the surface, two electrons become available for conduction through Ce 4f 1 states, thus increasing the number of Ce 3+ species ([CeO 8 ] O ′ ) on the right side of the equation, with the consequent decrease in resistance, as seen in Figure .…”

“…Additionally, we showed that a 8 wt % La-doped CeO 2 sample presented a significant dual sensing behavior when exposed to CO, with a response-time (tresp) of approximately 5 s and a reversibly optical reply close to 0.3 s, changing its surface color, close to 400 °C. This effect is intrinsically related to ferromagnetic, photoluminescent, and gas-sensing properties. Additionally, the electrical conduction of CeO 2 films is virtually dominated by cluster-to-cluster charge transfer (CCCT) processes, indicating an electron quantum tunneling/hopping mechanism on the film response, which stems from interaction between intrinsic vacancies among the clusters, such as [CeO 8 ] O ′...[CeO 7 ·V O •• ]...[CeO 8 ] O ′, which can still be present even above room temperature …”