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.
Dongxu Zhu,Aiwei Tang,Haihang Ye,Miao Wang,Chunhe Yang,Feng Teng
Colloidal djurleite nanocrystals exhibit a well-defined and strong localized surface plasmon resonance absorption in the near-infrared region, which arises from the excess free holes in the valence band. The near-infrared localized surface plasmon resonance absorption wavelength of the as-obtained djurleite nanocrystals can be modulated by varying their size and shape, which are controlled through the variation of the reaction conditions during the synthesis. For a given size, the plasmonic behavior of the spherical nanocrystals exhibits an obvious surface-dependent shift due to the different electron-donating abilities of the surface ligands, which leads to the change of hole density. Moreover, the plasmonic band of the djurleite nanocrystals shifts to a shorter wavelength upon exposure to air for longer time, during which no crystal structure is altered, and this blue-shift may be attributed to the increasing density of copper vacancies. The experimental results of the near-infrared plasmonic behavior are in good agreement with the calculated results based on the Mie–Drude model.
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