High-temperature ferromagnetism observed in facing-target reactive sputtered MnxTi1−xO2 films

The crystal structure of reactive sputtered MnxTi1−xO2 films turns from anatase to rutile as x increases. All the films are ferromagnetic, with a Curie temperature above 340K. Vacuum annealing enhances the ferromagnetism of the films, but O2 annealing weakens it, indicating that the ferromagnetism is related to the oxygen-vacancy defects created by Mn+2 dopants at Ti+4 cations. The average room-temperature moment per Mn decreases from 0.482μB at x=0.026 to 0.078 μB at x=0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35eV at x=0 to 1.73eV at x=0.375, suggesting that Mn ions substitute for Ti ions uniformly and the ferromagnetism is not from magnetic Mn oxide impurities. The high-temperature ferromagnetism makes the MnxTi1−xO2 films useful for the applications in spintronic devices.