Room-temperature ferromagnetism in Co and Nb co-doped TiO2 nanoparticles

Co- and Nb-doped TiO2 nanoparticles encapsulated with amorphous SiO2 were synthesized by our novel preparation method. An anatase TiO2 single-phase structure was confirmed using X-ray diffraction. The particle size could be controlled to be about 5 nm. The composition of these nanoparticles was investigated by X-ray fluorescence analysis. X-ray absorption near-edge structure spectra showed that the Ti4+ and Co2+ states were dominant in our prepared samples. A reduction in the coordination number was also confirmed. The dependence of the electrical conductivity on the frequency was measured by an LCR meter, and the carrier concentration was determined. The magnetization curves for the nanoparticles indicated ferromagnetic behavior at room temperature. We concluded that the ferromagnetism originated in oxygen vacancies around the transition metal ions.