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

TL;DR

This study investigates how niobium doping influences the ferromagnetism and microstructure of cobalt-doped anatase TiO2 films, revealing doping-dependent effects on magnetic properties and cobalt distribution.

Contribution

It demonstrates that niobium doping can either suppress or enhance ferromagnetism in Co:TiO2 films depending on growth conditions, with detailed microstructural analysis.

Findings

Niobium doping suppresses ferromagnetism at low oxygen pressure.

Niobium doping enhances ferromagnetism at higher oxygen pressure.

Cobalt-rich phases segregate without forming metallic cobalt clusters.

Abstract

It is shown that dilute niobium doping has 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^{-5} Torr niobium doping suppresses the ferromagnetism, while it enhances the same in films grown at 10^{-4} Torr. High-resolution Z-contrast Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy show uniform surface segregation of cobalt-rich Ti_{1-x-y}Co_{x}Nb_{y}O_{2-d} phase, but without cobalt metal clusters.