Effect of annealing temperature on structural and magnetic properties of Zn_0.94Co_0.05Cu_0.01O

The doped ZnO system Zn_0.94Co_0.05Cu_0.01O (ZCCO) was prepared as a nano-polycrystalline by a simple sol-gel process, then air annealed at different temperatures. Applying X-ray diffraction (XRD) and the Rietveld method, structural analysis showed that Co and Cu replace Zn substitutionally yielding ZCCO single phase. The refined u-fractional coordinate of Zn increases monotonically by an annealing temperature from 0.3546 at 500°C reaching 0.3722 at 800°C, very near from the ideal value 0.375. The Zn tetrahedrons become more symmetric and the distortion is gradually relieved by annealing up to 800°C. Annealing at 900°C introduces tetrahedron distortion in an opposite way. The zero field cooled (ZFC) and field cooled (FC) magnetization versus the temperature at different applied fields and the magnetization versus the applied field at different temperatures were carried out. The system exhibits a ferromagnetic behavior at room temperature. As the annealing temperature increases from 550 to 900°C, the saturation magnetization at 300 K increases from 0.0507 to 0.1088 emu/g.