Oxygen vacancy-mediated room-temperature ferromagnetism in insulating cobalt-substituted SrTiO 3 epitaxially integrated with silicon

Room-temperature ferromagnetic insulating behavior is demonstrated in cobalt-substituted SrTiO₃ grown on silicon. Ferromagnetism is exhibited by films with a composition of 30--40$%$ cobalt. Measurements of stoichiometry by x-ray photoelectron spectroscopy indicate Co replacing Ti with the concomitant creation of an approximately equal number of oxygen vacancies as the cobalt ions. First-principles modeling of this system shows that the observed local magnetic moment originates from a cobalt-oxygen vacancy complex with Co in the $+$2 valence state. The calculations also confirm the insulating nature of the material. The ability to deposit a room-temperature ferromagnetic insulator onto silicon may be useful for certain spintronics applications such as spin filters for spin-injection contacts.