Evidence of room temperature ferromagnetism in argon/oxygen annealed TiO₂ thin films deposited by electron beam evaporation technique

TiO₂ thin films deposited by electron beam evaporation technique annealed in either O₂ or Ar atmosphere showed ferromagnetism at room temperature. The pristine amorphous film demonstrates anatase phase after annealing under Ar/O₂ atmosphere. While the pristine film shows a super-paramagnetic behavior, both O₂ and Ar annealed films display hysteresis at 300 K. X-ray photo emission spectroscopy (XPS), Raman spectroscopy, Rutherford's backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were used to refute the possible role of impurities/contaminants in magnetic properties of the films. The saturation magnetization of the O ₂ annealed film is found to be higher than the Ar annealed one. It is revealed from shifting of O 1s and Ti 2p core level spectra as well as from the enhancement of high binding energy component of O 1s spectra that the higher magnetic moment is associated with higher oxygen vacancies. In addition, O ₂ annealed film demonstrates better crystallinity, uniform deposition and smoother surface than that of the Ar annealed one from glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM). We conclude that although ferromagnetism is due to oxygen vacancies, the higher magnetization in O₂ annealed film could be due to crystallinity, which has been observed earlier in Co doped TiO₂ film deposited by pulsed laser deposition (Mohanty et al., 2012 [10]).