Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2

Electric and magnetic properties of a high-temperature ferromagnetic oxide semiconductor, cobalt-doped rutile TiO2, are summarized. Cobalt-doped rutile TiO2 epitaxial thin films with different electron densities and cobalt contents were grown on r-sapphire substrates with laser molecular beam epitaxy. Results of magnetization, magnetic circular dichroism and anomalous Hall-effect measurements were examined for samples with systematically varied electron densities and cobalt contents. The samples with high electron densities and cobalt contents show high-temperature ferromagnetism, suggesting that charge carriers induce the ferromagnetism.