The magnetic properties of Co-doped ZnO diluted magnetic insulator films prepared by direct current reactive magnetron co-sputtering

Co-doped ZnO ferromagnetic films were prepared by direct current reactive magnetron co-sputtering at significantly low growth temperature (∼200∘C). Employing complementary characterization we show that a solid solution of Co throughout the ZnO films, where Co is in the 2+ state substituting for Zn. Room temperature ferromagnetism with magnetic moment of 1.1μB/Co and a high Curie temperature TCTC of 750 K are observed in (4 at%) Co:ZnOCo:ZnO films, which is not carrier mediated, but co-exists with the dielectric state. The combination of film growth by certain concentration of cobalt doping (∼4at%) and low growth temperature deposition is proved to be key in enhancing the ferromagnetism. The mechanisms responsible for the ferromagnetism in insulating Co:ZnOCo:ZnO films are discussed, which is of help for a better understanding of ferromagnetism in transition-metal-doped oxides.