Fe valence states and ferromagnetism occurring in reduced anatase Ti_(0.97)Fe_(0.03)O_(2-delta)

摘要

Fe-doped anatase TiO_2 polycrystalline films and powders have been prepared by the sol-gel method. Air-annealed film shows paramagnetic behavior at room temperature. However, when the film is further annealed in a vacuum, the ferromagnetic properties are strongly enhanced with the magnetic moment of 0.42 mu_B/Fe at 5 kOe. Mossbauer spectrum of air-annealed film at 295 K shows a single doublet of Fe~(3+). On the other hand, the absorption spectrum after vacuum annealing exhibits two doublets, in which one is the same component with air-annealed case and the other is a new doublet corresponding to Fe~(2+) state. The temperature dependence of absorption linewidth and quadrupole splitting for the Fe~(2+) doublet indicates that Fe~(2+) ions are not paramagnetic and their magnetic" interaction exists also at 295 K.