Substrate effects on the room-temperature ferromagnetism in Co-doped TiO_2 thin films grown by pulsed laser deposition

Co:TiO_2 films were fabricated by laser ablation on Si, LaAlO_3 (LAO), and SrTiO_3 (STO) substrates from a ceramic target. Films on all types of substrates have Curie temperature (T_C) above 400 K. All films are highly crystallized with different structures. While films on Si substrates are rutile, films on LAO and STO substrates are single phased anatase. Due to the different lattice mismatch, films grown under the same growth conditions on Si, LAO, and STO substrates have different saturation magnetization and coercivity. While Co atoms are mostly localized near the surface of the films, magnetic measurements suggested that the ferromagnetism unlikely originates from Co clusters