Structural and Magnetic Properties of Codoped ZnO based Diluted Magnetic Semiconductors

Zn_1-xCo_xO (x=0.01, 0.02, 0.05, 0.10 and 0.20) diluted magnetic semiconductors are prepared by the sol-gel method. The structural and magnetic properties of the samples are studied using x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS) and superconducting quantum interference device (SQUID). The XRD patterns does not show any
signal of precipitates that are different from wurtzite type ZnO when Co content is lower than x=0.10. An EXAFS technique for the Co K-edge has been employed to probe the local structures around Co atoms doped in ZnO powders by fluorescence mode. The simulation results for the first shell EXAFS signals indicate that Zn sites can be substituted by Co atoms when Co content is lower than x=0.05. The SQUID results show that the samples (x<0.05) exhibit clear hysteresis loops at 300K, and magnetization versus temperature from 5K to 350K at H=100,Oe for the sample x=0.02 shows
that the samples have ferromagnetism above room temperature. A double-exchange mechanism is proposed to explain the ferromagnetic properties of the samples.