Defect-mediated ferromagnetism in insulating Co-doped anatase TiO2 thin films

The nature of the defect responsible for room-temperature ferromagnetism in Co-doped anatase TiO(2) has remained elusive. Here we report atomic-resolution Z-contrast images of epitaxially grown Co(0.03):TiO(2) films showing that Co atoms are dispersed and occupy preferred interstitial sites. Density-functional calculations found that these sites are the lowest-energy configuration of Co in anatase and that O vacancies (V(O)), introduced by annealing, anchor the Co atoms into Co-Ti(+3)-V(O) complexes. The calculated magnetic moment is in agreement with our measured value and the calculated Co x-ray absorption spectrum is in agreement with data published in the literature.