Cr-doped TiO2 anatase: A ferromagnetic insulator

Epitaxial ferromagnetic films of Cr-doped $\mathrm{Ti}{\mathrm{O}}_2$ anatase $\left({\mathrm{Cr}}_x{\mathrm{Ti}}_{1-x}{\mathrm{O}}_{2-x∕2}\right)$ were grown on $\mathrm{La}\mathrm{Al}{\mathrm{O}}_3\left(001\right)$ using oxygen-plasma-assisted molecular-beam epitaxy. $\mathrm{Cr}K$ -shell x-ray absorption near-edge spectroscopy shows that the formal oxidation state of Cr is +3 throughout the films, with no evidence for either elemental Cr or half-metallic $\mathrm{Cr}{\mathrm{O}}_2$ . Cr is found to substitute for Ti in the lattice, with uniform distribution throughout the doped region of the film. The Cr-doped anatase films exhibit room-temperature ferromagnetism aligned in-plane, with a saturation magnetization of $\sim 0.6{\mathrm{\mu }}_{\mathrm{B}}$ /Cr atom.