Structural and magnetic properties of Zn_0.95Cr_0.05O annealed at different temperatures

The doped ZnO system Zn_0.95Cr_0.05O (ZCO) was prepared as nano-polycrystalline by a simple sol-gel process and annealed at different temperatures. Structural and microstructure analyses are performed by applying x-ray diffraction (XRD) and Rietveld method. Results showed that Cr ions reside in the ZnO lattice substitutionally for Zn yielding ZCO single phase. The Rietveld refined u-fractional coordinate of Zn/Cr decreased with the annealing temperature from 0.3879 Å at 400 °C to 0.3740 Å at 600 °C. The Zn tetrahedrons become more symmetric and the distortion is gradually relieved by annealing. The field cooled (FC) and zero field cooled (ZFC) magnetization versus temperature and the magnetization versus applied field at different temperatures were carried out. Measurements indicated that the absence of ferromagnetic behavior with magnetization slightly changed by changing the annealing temperature and no saturation. The Curie-Weiss paramagnetic temperature θ for annealed samples is negative indicating the antiferromagnetic nature of the samples.