Probing the Role of Dopant Oxidation State in the Magnetism of Diluted Magnetic Oxides Using Fe-Doped In2O3 and SnO2 Nanocrystals

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• 作者：Natalie S. Garnet ; Vahid Ghodsi ; Lisa N. Hutfluss ; Penghui Yin ; Manu Hegde ; Pavle V. Radovanovic
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 26, 2017
• 年：2017
• 卷：121
• 期：3
• 页码：1918-1927
• 全文大小：597K
• ISSN：1932-7455

文摘

Investigation of the origin of high-Curie temperature ferromagnetism in diluted magnetic oxides has become one of the focal points of research on solid-state magnetism. While several possible mechanisms have been proposed theoretically, broader experimental evidence is still lacking. Here we report a comparative study of the electronic structure and magnetic properties of colloidal Fe-doped In₂O₃ and SnO₂ nanocrystals, as building blocks for grain-boundary-rich diluted magnetic oxide films. The dopant ions in both nanocrystal host lattices are principally in 3+ oxidation state, with possibly a minor presence of Fe²⁺ in In₂O₃, and no conclusive evidence of the presence of Fe²⁺ in SnO₂ nanocrystals. Subsequently, we found that Fe-doped In₂O₃ nanocrystalline films exhibit only minor ferromagnetic ordering (with a magnetic moment of less than ca. 0.1 μ_B/Fe) and decreasing saturation magnetization with increasing doping concentration at room temperature. The saturation magnetic moment of Fe-doped SnO₂ nanocrystalline films is insignificant or below the detection limit. These results contrast previous findings for analogous Mn-doped nanocrystals, which contain mixed oxidation states (Mn²⁺ and Mn³⁺) and exhibit a robust ferromagnetism at room temperature. The correlation between the mixed dopant oxidation states and the observed magnetic properties implies that ferromagnetism in these systems is of a Stoner type, enabled by electron transfer between dopant ions and the local defect states arising from the grain boundaries within a nanocrystalline film. These results suggest the prospect of probing and manipulating ferromagnetism in nonmagnetic oxides by simultaneous control of the transition metal dopant oxidation states and extended structural defects.