Effect of annealing on the structural and magnetic properties of sol-gel synthesized Co doped ZnO

Nanocrystalline powders of undoped ZnO and Co (5w%) doped ZnO are synthesized successfully by employing soft chemical route. The structural, vibrational and magnetic properties as a function of calcination temperatures (400-1100 degrees C) are studied by using various characterization techniques. The X-ray diffraction study has clearly revealed the evolution of the major wurtzite phase (ZnO) in addition to the secondary nanocrystalline cubic spinet phase of CO3O4 is observed at 800 degrees C which grows upto 1100 degrees C. FTIR study supports the existence of the metal cation-oxygen bonding due to secondary cubic spinet Co3O4 phase. At lower calcination temperature (800 degrees C), predominant paramagnetic behavior is demonstrated, though secondary cubic spinet phase of Zn(x)Co3-xO(4) is present. With the increase in calcination temperature (1100 degrees C), an enhanced paramagnetic behavior is observed as paramagnetic bulk cubic spinet Zn(x)Co3-xO(4) phase effectively increases the effective magnetic moment. The occurrence of paramagnetic behavior with the increase in annealing temperature is understood on the basis of inverted cubic spinet, exchange interactions and occupancy of cobalt ions in both tetrahedral and octahedral sites. With the presence of the non-magnetic secondary nanocrystalline and bulk Zn(x)Co3-xO(4) spinet phase, Co (5w%) doped ZnO cannot be used as diluted magnetic semiconductor based spintronics devices.