Magnetic properties of Fe doped, Co doped, and FeCo co-doped ZnO

The structural, electronic, and magnetic properties of Zn _0.95Co_0.05O, Zn_0.95Fe_0.05O, and Zn_0.90Fe_0.05Co_0.05O 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 Zn ² ions in tetrahedral sites. ⁵⁷Fe Mössbauer spectroscopy showed the presence of isolated paramagnetic Fe³ ions in both Fe doped and FeCo co-doped ZnO, however, no evidence of ferromagnetically ordered Fe³ ions is observed. In the Zn_0.95Fe _0.05O sample, weak presence of ZnFe₂O₄ was detected as an impurity phase, whereas Zn_0.90Fe_0.05Co _0.05O was impurity-free within detection limit in all those measurements. Results of these studies suggest that Fe and Co ions in the FeCo 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 Zn_0.90Fe_0.05Co_0.05O, leading to the enhanced ferromagnetism observed in this sample. However, more evidence is necessary to confirm the role of charge transfer ferromagnetism.