Raman spectroscopy of Cu doping in Zn_1-xCo_xO diluted magnetic semiconductor

The room-temperature ferromagnetism and the Raman spectroscopy of the Cu-doped Zn_1-xCo_xO powders prepared by the sol-gel method are reported. The x-ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization-field curves measured at room temperature demonstrated that all Co-doped ZnO powders were paramagnetic.Ferromagnetic ordering is observed for the samples doped with Cuin Zn_o.98Co_0.02O and strongly depends on the concentration of Cu. The relative strength of the second-order LO peak to the first-order one in the Raman spectra, which is related to the carrier concentration, of the Cu-doped Zn_o.98Co_0.02O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman-Kittel-Kasuya-Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system.