The structural, electronic, and magnetic properties of Zn0.95Co0.05O, Zn0.95Fe0.05O, and Zn0.90Fe0.05Co0.05O nanoparticles prepared by a sol-gel method are presented and discussed. X-ray diffraction and optical analysis indicated that high spin Co2+ ions substitute for the Zn2+ ions in tetrahedral sites. 57Fe Mössbauer spectroscopy showed the presence of isolated paramagnetic Fe3+ ions in both Fe doped and Fe+Co co-doped ZnO, however, no evidence of ferromagnetically ordered Fe3+ ions is observed. In the Zn0.95Fe0.05O sample, weak presence of ZnFe2O4 was detected as an impurity phase, whereas Zn0.90Fe0.05Co0.05O was impurity-free within detection limit in all those measurements. Results of these studies suggest that Fe and Co ions in the Fe+Co co-doped sample has a strong synergistic effect because they eliminated the presence of impurities and gave the strongest ferromagnetic signal. Possible role of charge transfer ferromagnetism involving mixed valence ions is considered as a potential mechanism in these nanoparticles. Presence of both Co2+ and Fe3+ might promote more efficient charge transfer in the co-doped Zn0.90Fe0.05Co0.05O, leading to the enhanced ferromagnetism observed in this sample. However, more evidence is necessary to confirm the role of charge transfer ferromagnetism.
Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, Volume 113, Issue 17, (2013) and may be found at http://dx.doi.org/10.1063/1.4799778.
Beltrán, J. J.; Osorio, J. A.; Barrero, C. A.; Hanna, Charles B.; and Punnoose, A.. (2013). "Magnetic Properties of Fe Doped, Co Doped, and Fe+Co Co-Doped ZnO". Journal of Applied Physics, 113(17), 17C308-1-17C308-3.