Clarifying the origin of green photoluminescence and the room temperature ferromagnetism in ZnO is crucial for its potential application. In this work, we show that the characteristic 368 nm donor-bound exciton and the g = 1.96 electron spin resonance (ESR) signal in ZnO nanocrystals were eliminated after H2O2 oxidation, along with the appearance of 550 nm photoluminescence, unambiguously evidencing the creation of acceptor defects. Meanwhile, the d0 ferromagnetism was significantly enhanced. In combination with the fact that ambient O2 exposure also resulted in a significant boost of ferromagnetism in ZnO particles with different grain sizes, we surmise that adsorbed oxygen facilitates the d0 ferromagnetism in ZnO while VZn causes the 550 nm green emission. This work illustrates that oxygen exposure is an efficient way to tune the physics in metal oxides through engineering defects.
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.
With the development of spintronics, ferromagnetic nanomaterials have shown unique advantages in the fields of information storage and quantum computation. The ABO3-type perovskite oxide ZnSnO3 is expected to realize d0 ferromagnetism due to its tunable crystal structure and unique electron arrangement. In this work, for the first time, the inhomogeneous oxygen octahedral structural distortion along the c-axis induced by SC CO2 can be found in 2D ZnSnO3, i.e., distortion of ZnO6 is larger than that of SnO6, and they are served as the structural basis for the generation of room-temperature ferromagnetism. In addition, combining the change in the concentration of the oxygen vacancies to ultimately realize the room-temperature d0 ferromagnetism in ZnSnO3 (Tc = 400 K, Ms = 0.1123 emu/g) can be presented. Therefore, this study establishes a new strategy for the development of transition metal-free ferromagnetic materials for the application of spintronic devices at room temperature.
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