Tailoring of Magnetic Properties of Nanocrystalline and Amorphous Tio2 : Fe Upon Al Doping

The work is devoted to the study of the magnetic properties and electronic structure of TiO 2 : Fe, Al nanopowders, which are promising for solving various applied problems. The sol-gel methods used to obtain the nanopowders in both crystalline (average size from 3 to 20 nm) and X-ray amorphous states. The electron paramagnetic resonance and magnetic properties of TiO 2 : Fe, Al nanopowders are studied. The electron paramagnetic resonance spectra of crystalline samples TiO 2 : Fe doped with aluminum besides a resonance line with g-factor ~ 2 exhibit resonance with a g-factor of 4.3 from Fe 3+ ions with rhombohedral distortions. The fraction of Fe 3+ with rhombohedral distortions increases with increasing aluminum content. For the amorphous state at Al doping, the resonance with a g-factor of 4.3 is completely dominant in the electron paramagnetic resonance spectrum. The density functional theory calculation shows that aluminum prefers to be localized near iron ions, distorting the nearest Fe 3+ environment. The complex integral electron paramagnetic resonance spectrum of all samples was fitted with a sufficient accuracy by three separate resonance lines with different widths and intensities. The temperature dependence of the integral intensity of ​​above separate resonance components is investigated and it was established that electron paramagnetic resonance spectrum can be described by the coexistence of paramagnetic centers (isolated Fe 3+ ions) and iron clusters with negative exchange interactions