Ferromagnetism Induced by Clustered Co in Co-Doped AnataseTiO2Thin Films

We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase ${\mathrm{T}\mathrm{i}\mathrm{O}}_2$ thin film, using the magnetic circular dichroism (MCD) at the Co $L_{2,3}$ absorption edges. The magnetic moment was observed to be $\sim 0.1{\mu }_B/\mathrm{C}\mathrm{o}$ in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at $\sim 400°\mathrm{C}$, the MCD signal increases, and the moment reaches up to $\sim 1.55{\mu }_B/\mathrm{C}\mathrm{o}$, which is $\sim 90\%$ of the moment in Co metal. In the latter case, the cluster size was observed to be 20–60 nm.