Giant magnetic moment in an anomalous ferromagnetic insulator: Co-doped ZnO

Ferromagnetic insulators that exhibit strong ferromagnetism at the atomic level are believed to be suitable for magnetic dielectric barriers in spintronic devices and solid-state qubits in quantum computing. Here a giant magnetic moment of 6.1 mu(B)/Co and a high Curie temperature T-C of 790 K are observed in (4 at. %) Co-doped ZnO films, which is not carrier mediated, but co-exists with the dielectric state. Direct current reactive magnetron co-sputtering is used to grow Zn0.96Co0.04O dilute magnetic insulator on LiNbO3 (104) substrates at considerably low growth temperature (similar to 200 degrees C), which is significant for complementary metal oxide semiconductor technology. X-ray photoelectron spectroscopy and x-ray-absorption spectroscopy reveal a solid solution of cobalt in ZnO, where Co is in the 2+ state substituting for Zn. A supercoupling mechanism in terms of bound magnetic polarons is proposed to discuss the ferromagnetism in the dielectric ground state of Co:ZnO, which would lead to different consideration for the origin of giant magnetic moment and high-temperature ferromagnetism in transition-metal doped oxides.