Raman spectroscopy of Cu doping in Zn1−xCoxO 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 Cu in Zn_0.98Co_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_0.98Co_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. Copyright © 2009 John Wiley & Sons, Ltd.