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

The room temperature d 0 ferromagnetism origin is still highly controversial in oxide systems, due to the lack of subtle experimental set-up as well as sensitive defect detection. Herein, we developed O-rich treatments on Ceria nanocrystals , H 2 O 2 and O 2 ambient exposure, which creates intrinsic O defects without introducing trace level of impurities or changing crystallinity. Interestingly, results found that significant oxygen adsorption along with distinct augment of RT ferromagnetism were observed after both H 2 O 2 treatment and O 2 ambient exposure. The more the oxygen molecule adsorbed, the stronger the ferromagnetism was. Furthermore, Electron Spin Resonance (EPR) results illustrate that the Ce 3+ concentration experienced reverse variation in H 2 O 2 treated-and O 2 exposed-samples, thus excluding the possibility of Ce cation as the cause of the ferromagnetism. Similar magnetism enhancements were also observed in La 2 O 3 , ZrO 2 and SrTiO 3 nanocrystals after H 2 O 2 treatment. Based on these results, we surmise that the interstitial oxygen, rather than the other sources, facilitated the electron transfer and the dilute ferromagnetism of CeO 2 . This work established a general model in clarifying the origin of the disputed ferromagnetism in metal oxide system.