Investigation of the cobalt distribution in the room temperature ferromagnet TiO2:Co

Recent reports of room temperature ferromagnetism in thin films of TiO2 doped with small amounts of cobalt have excited a great deal of interest due to the possible applications of this ferromagnetic, transparent semiconductor to spintronics devices. Ferromagnetism has been reported for TiO2 grown in both the anatase and rutile phases, although a range of magnetic moments has been reported by different groups. We have grown epitaxial thin films of Ti1-xCoxO2, with x=0.01-0.07 by pulsed laser deposition in both the anatase and rutile forms on single crystal substrates of LaAlO3, SrTiO3, and Al2O3. These films are ferromagnetic at room temperature with a magnetic moment of similar to1.7 mu(B)/Co in the anatase phase and similar to0.6 mu(B)/Co in the rutile phase. Detailed transmission electron microscopy measurements show a variation in the cobalt distribution in these materials that corresponds to the different magnetic moments. The cobalt does not appear to enter the anatase phase of TiO2, but rather forms crystallites of cobalt metal on the surface of anatase films. This results in a magnetic moment similar to that of bulk cobalt. In the rutile phase the cobalt has substituted uniformly throughout the lattice. We present the morphology and magnetization of TiO2:Co as a function of the TiO2 growth phase and substrate material. Preliminary electrical measurements are also mentioned. (C) 2003 American Institute of Physics.