Tailoring the magnetization behavior of Co-doped titanium dioxide nanobelts

Cobalt-doped titanium dioxide nanobelts which showed room temperature ferromagnetism were prepared from a ferromagnetic rutile TiO2 single crystal. The ferromagnetic ordering in these nanobelts was found to be mediated in the presence of bulk oxygen vacancies. These oxygen vacancies could be engineered by annealing the as-synthesized Co-doped titanate nanobelts under vacuum at higher temperatures. The sole presence of this type of vacancy was achieved when the titanate nanobelts were transformed into the monoclinic TiO2-B phase in which saturated magnetization was also observed. Annealing these nanobelts into the anatase phase caused the formation of other defect and active sites, such as surface and bulk Ti3+ species, which caused the non-saturation of magnetic moments in the magnetization curves. Ferromagnetism was suppressed when the Co-doped titania nanobelts were annealed in air due to the diminishing of the amount of oxygen vacancies.