Growth of Cr-doped TiO2 films in the rutile and anatase structures by oxygen plasma assisted molecular beam epitaxy

As part of a search for new spintronic materials, highly ordered films of CrxTi1−xO2 in both the rutile and anatase structures and for several Cr concentrations ranging from x = 0.02 to 0.16 were grown by oxygen plasma assisted molecular beam epitaxy. X-ray photoelectron diffraction data of the Cr 2p level exhibit the same patterns and the same modulation amplitudes as those observed for Ti 2p, providing a strong indication that a large fraction of the Cr atoms occupy substitutional lattice sites in both structures. The Cr 2p core-level spectra as well as a Cr 3d related dopant signal above the valence band of TiO2 are characteristic of Cr3+ ions. At room temperature, Cr-doped anatase films exhibit ferromagnetic order with a saturation magnetization of ∼0.6 μB per Cr atom and strong in-plane anisotropy.