Evolution of structural and magnetic properties of Ar2 ion irradiated TiO2 thin films annealed under argon atmosphere

摘要

In this report, the evolution of structural as well as magnetic state of 900 °C annealed TiO 2 films under argon (Ar) environment have been examined before and after irradiating with the Ar 2 ions of energy 500 keV. The pristine film stabilized with Magneli phase (Ti 4 O 7 ), the film retains its crystallinity but phase get transformed to anatase TiO 2 , irradiating with the lowest fluence, 1 × 10 14 ions/cm 2 . After rising up to 5 × 10 16 ions/cm 2 ion fluence, film again stabilize with the Magneli phase (Ti 4 O 7 ). In the previous report, we have demonstrated an unusual phase change from anatase TiO 2 to brookite, where films are annealed in O 2 atmosphere. In contrast to that here we have obtained TiO 2 from Ti 4 O 7 at lowest fluence but at highest fluence again Ti 4 O 7 is obtained. The energy deposited by the ion beam passed to the lattice and collision cascades are formed which brings atomic displacement in the lattice, results the structural transformation. Surface topography is not affected much after the irradiation as observed from atomic force microscopy (AFM). Interesting, ferromagnetic behavior at room temperature stems in all the films as a consequence of the controlled introduction of anionic defects (oxygen vacancies).