Ferromagnetism in cobalt-doped SrTiO3 on Si grown by molecular beam epitaxy

We report the epitaxial growth of ferromagnetic cobalt-doped SrTiO$_{3}$ directly on silicon without the use of any buffer by molecular beam epitaxy (MBE). Magnetization as a function of magnetic field was performed for samples with varying doping concentration at room temperature and at 10 K. Room-temperature ferromagnetism is confirmed in single phase samples with composition 20-30\% cobalt. We also performed x-ray photoelectron spectroscopy of the Co and Ti 2p levels to determine stoichiometry and cobalt oxidation state. In order to elucidate the origin of ferromagnetism, we also performed first-principles calculations of cobalt-doped SrTiO$_{3}$ with different doping concentrations and dopant configurations. The calculations show that intrinsic ferromagnetism can be stabilized beyond a critical concentration in SrTiO$_{3}$ under particular conditions. The ability to directly integrate a ferromagnet on silicon in epitaxial form may potentially overcome the problems of impedance mismatch and interface losses in applications involving spin injection in silicon.