Oxygen Vacancy as a Medium-Induced Ferromagnetism in (Fe, Sb) Codoped SnO2 Films

(Sn0.97–xSb0.03Fex)O2 films (x = 0, 0.024, 0.046, and 0.073) were prepared by radio frequency magnetron sputtering. The structural environment, electrical transport, and magnetic behavior of the films were studied by X-ray diffractometer, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure, physical property measurement system, electron paramagnetic resonance (EPR), and superconducting quantum interference methods. All of the films exhibited the tetragonal rutile structure of SnO2 by X-ray diffraction. XPS and extended X-ray absorption fine structure measurements revealed that Fe-doping ions substitute for Sn4+ sites of SnO2 lattice with a mixed-valence (Fe2+/Fe3+) and no trace of Fe cluster or second phases are in the doped system. The electrical transport measurement showed that the films have a typical semiconductor characteristic and that the carrier concentration nc decreases monotonically with Fe-doped concentration, and the carriers are strongly localized. Magnetic measurement showed that the saturation magnetization of the films increases regularly with Fe-doped concentration at room temperature. On the basis of EPR analysis, with an increase of Fe-doped concentration, the number of oxygen vacancies (Vo+) increases. The oxygen vacancies result in a long-range ferromagnetic ordering of the codoped SnO2 films. The origin of ferromagnetism of the codoped SnO2 films can be attributed to bound magnetic polaron mechanism.