Clustering-induced high magnetization in Co-doped TiO2

High magnetization materials are highly desirable for the development of advanced multifunctional magnetic applications. Co:TiO2 is a widely investigated diluted magnetic semiconductor (DMS) system which persists ferromagnetism to above room temperature. However, the magnetic moment observed in Co:TiO2 so far typically lays between 0.01 μB per Co atom to the Co bulk value, 1.7 μB/Co, while higher saturation magnetization (Ms) surpasses 2 μB/Co which has only occasionally been reported. The huge magnetization difference suggests formation of Co nanoclusters is poorly controlled and immensely dependent on growth parameters. In this work, 5 at% Co-doped TiO2 thin films on SrTiO3 substrate were deposited via pulsed laser deposition. By delicately choosing the deposition parameters, various sized Co nanoclusters are embedded into TiO2 thin films with unique surface nanostructures. The Co nanoclusters show metallic features, confirmed by X-ray photoelectron spectroscopy. Moreover, the thin films exhibit excellent cluster-dependent Ms, reaching 2.5 μB/Co under optimal parameters. This work provides an effective approach to design high magnetization thin films with various surface morphology.