Defect-Mediated Ferromagnetism in Insulating Co-Doped Anatase TiO2Thin 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 003 :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 0 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.