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Role of oxygen defects on the magnetic properties of ultra-small Sn 1x Fe x O 2 nanoparticles
| Content Provider | Semantic Scholar |
|---|---|
| Author | Dodge, Kelsey Punnoose, Alex |
| Copyright Year | 2013 |
| Abstract | Although the role of oxygen defects in the magnetism of metal oxide semiconductors has been widely discussed, it’s been difficult to directly measure the oxygen defect concentration of samples to verify this. This work demonstrates a direct correlation between the photocatalytic activity of Sn1-xFexO2 nanoparticles and their magnetic properties. For this, a series of ~2.6 nm sized, well characterized, single-phase Sn1-xFexO2 crystallites with x=0-0.20 were synthesized using tin acetate, urea, and appropriate amounts of iron acetate. XPS confirmed the concentration and 3+ oxidation state of the doped Fe ions. The maximum magnetic moment/Fe ion, μ, of 1.6x10μB observed for the 0.1% Fe doped sample is smaller than the expected spin-only contribution from either high, or low spin Fe ions, and μ decreases with increasing Fe concentration. This behavior cannot be explained by the existing models of magnetic exchange. Photocatalytic studies of pure and Fe-doped SnO2 were used to understand the roles of doped Fe ions and of the oxygen vacancies and defects. The photocatalytic rate constant k also showed an increase when SnO2 nanoparticles were doped with low concentrations of Fe, reaching a maximum at 0.1% Fe, followed by a rapid decrease of k for further increase in Fe%. Fe doping presumably increases the concentration of oxygen vacancies, and both Fe ions and oxygen vacancies act as electron acceptors to reduce e h recombination and promote transfer of electrons (and/or holes) to the nanoparticle surface, where they participate in redox reactions. This electron transfer from the Fe ions to local defect density of states at the nanoparticle surface could develop a magnetic moment at the surface states and leads to spontaneous ferromagnetic ordering of the surface shell under favorable conditions. However, at higher doping levels, the same Fe ions might act as recombination centers causing a decrease of both k and magnetic moment μ. Metal oxide semiconductors such as SnO2, ZnO and TiO2 have been investigated extensively in recent years following theoretical predictions that doping with transition metal (TM) ions could produce ferromagnetism at room temperature [1,2]. Room temperature ferromagnetism (RTFM) has been reported in several oxide semiconductor systems [3], not only in those that contain transition metal dopants [4], but even in undoped oxides [5,6]. Even after a decade-long research, the actual mechanism of ferromagnetism in these materials is still not understood, although hints about some of the key factors that contribute to the magnetism have been revealed. RTFM was observed in several undoped oxide semiconductors, however, their magnetization increased systematically when doped with increasing concentrations of TM ions [4,7], thus highlighting that TM ions still play a role. RTFM in these oxides are mostly observed in samples that are prepared in nanostructured form, with no ferromagnetism when bulk crystals are doped with TM ions. It is believed that oxygen vacancies and defects play a major role in the RTFM of semiconductor oxides; however demonstration of a direct correlation between the magnetism, dopant concentration and oxygen vacancies/defects has been difficult. Because of This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Journal of Applied Physics, published by American Institute of Physics. Copyright restrictions may apply. DOI: 10.1063/1.4794140. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1131&context=physics_facpubs |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
