Bound magnetic polarons and p-d exchange interaction in ferromagnetic insulating Cu-doped ZnO

A systematic study on the magnetic and electrical transport properties of single-phase wurtzite Zn1-xCuxO is performed. Efros variable range hopping dominates the conduction, which is accompanied by a ferromagnetic order up to 700 K for x > 1%. Both the first-principles calculations and Cu/Al co-doping experiments suggest that the spontaneous spin polarization originates from the p-d exchange interaction between O 2p and Cu 3d orbitals. Furthermore, our results are consistent with the scenario that the intrinsic ferromagnetism is established through indirect interactions between bound magnetic polarons mediated by magnetic impurities. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3579544]