Clusters and magnetism in epitaxial Co-doped TiO2 anatase

We show that under certain conditions, highly Co-enriched TiO2 anatase clusters nucleate on epitaxial TiO2 anatase grown on LaAlO3(001) by oxygen plasma assisted molecular beam epitaxy. In the most extreme cases, virtually all incident Co segregates to the clusters, yielding a nanoscale ferromagnetic phase that is not ferromagnetic in homogeneous films of the same Co concentration. The nucleation of this phase simultaneous with continuous epitaxial film growth must be carefully monitored in order to avoid drawing false conclusions about the film structure.