aTianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Institute of Advanced Materials Physics, Faculty of Science, Tianjin University, No. 92 Weijin Road, Nankai District, Tianjin 300072, China
Available online 24 April 2008.
Abstract
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 340 K. 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 0.482 μB at x = 0.026 to 0.078 μB at x = 0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35 eV at x = 0 to 1.73 eV 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.
Keywords: Compound semiconductors; Magnetic thin films; Magnetic properties; Vacancies; Optical transmission
Fig. 1. XRD patterns of as-deposited MnxTi1−xO2 films with different x: (a) 0, (b) 0.026, (c) 0.048, (d) 0.066 and (e) 0.176. The inset is the XRD pattern of Mn0.066Ti0.934O2 films annealed in vacuum at 500 °C for 2 h.
Fig. 2. M–H curves of as-deposited MnxTi1−xO2 films with x = 0.066 at different temperatures. The insets are the ZFC and FC curves of the films with x = 0.066 at 500-Oe field (bottom right) and the variation of moment per Mn with x (top left).
Fig. 3. Typical Mn2p XPS spectra for as-deposited MnxTi1−xO2 films with different x.
Fig. 4. Room-temperature M–H curves of as-deposited and 500 °C annealed MnxTi1−xO2 films with x = 0.066.
Fig. 5. Transmission spectra of MnxTi1−xO2 films with different x.
Fig. 6. Dependence of 
on photon energy for MnxTi1−xO2 films with different x. The inset gives the derived optical band gap values.
Table 1.
Lattice parameters calculated from the XRD patterns of anatase and rutile phases in the MnxTi1−xO2 films
