Dose dependence of magnetism in Co-doped TiO2

The dose dependence of magnetism in Co-implanted TiO2 rutile was investigated using the magneto-optic Kerr effect method at room temperature. The (100)- and (001)-oriented single-crystalline rutile TiO2 plates were used as substrates and implanted by Co ions with a varying dose range of 0.25–1.50×1017 ions/cm2. We observed paramagnetic behaviour for the low dose doped samples, but obtain clear hysteretic-like behaviour for intermediate and high dose doped samples. For the intermediate implantation doses of Co, ferromagnetic behaviour can be explained by the F-center (oxygen vacancies) exchange mechanism, while for the highest implantation dose, in addition to Co substitution on Ti sites, formation of Co nanoclusters may take place within the TiO2 irradiated region.