Magnetic Properties of N- and (Cr, N)-Doped TiO2 Nanoparticles

The effect of N and Cr doping on the magnetic properties of TiO₂ nanoparticles is analyzed in this paper. N- and (Cr, N)-doped TiO₂ nanoparticles were synthesized by the sol-gel method using titanium tetraisopropoxide as metallic precursor, and urea and chromium nitrate as N and Cr doping precursors, respectively. The calcined nanoparticles were analyzed through X-ray diffraction and Rietveld refinement. The samples display an anatase structure with mean grain sizes ~5 nm. A distortion of the anatase cell is detected (increase and decrease of a and c lattice parameters, respectively) with respect to the reported anatase bulk values. The room-temperature hysteresis loops of the samples display the coexistence of the paramagnetic and the ferromagnetic contributions. An enhancement in the ferromagnetic component is observed upon Cr and N codoping. The analysis of the temperature dependence of the magnetization confirms the coexistence of both the paramagnetic and the ferromagnetic contributions. Although the existence of a secondary phase cannot be completely excluded in the (Cr, N)-doped sample with the highest nitrogen content, the results confirm the achievement of intrinsic room temperature ferromagnetism in these doped semiconductor nanostructures.