Consequences of niobium doping for the ferromagnetism and microstructure of anatase Co:TiO2 films

Abstract

It is shown that dilute niobium doping has a significant effect on the ferromagnetism and microstructure of dilutely cobalt-doped anatase TiO2 films. Epitaxial films of anatase TiO2 with 3% Co, without and with 1% niobium doping were grown by pulsed-laser deposition at 875°C at different oxygen pressures. For growth at 10−5Torr niobium doping suppresses the ferromagnetism, while it enhances the same in films grown at 10−4Torr. High-resolution Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy show uniform surface segregation of cobalt-rich Ti1−x−yCoxNbyO2−δ phase, but without cobalt metal clusters.