Properties of ZnO Prepared by Polymeric Citrate Amorphous Precursor Method: An Influence of Cobalt Concentration

This study aims to investigate the vibrational, structural, morphological, optical and magnetic properties of Zn1-xCoxO with 0.00x0.05, prepared by sol-gel method via amorphous citrate precursor. FTIR spectroscopy has been used to follow the mecha-nism of thermal decomposition process of ZnO precursor. XRD and FTIR-ATR tech-niques showed only the single wurtzite crystalline phase with the presence of oxygen deficiency and/or vacancies, and secondary phases were not detected. SEM micro-graphs shown agglomerated particles of irregular shape and size with a high distribu-tion, evidenced particles of nanometric size with a morphology change for x=0.05. We detected high spin Co2+ ions located in tetrahedral core and pseudo-octahedral surface sites, substituting Zn2+ ions. The energy band gap of the ZnO semiconductor decreases gradually by increasing the Co doping concentration. M vs H for undoped ZnO nano-particles exhibited a diamagnetic overlapped with a weak ferromagnetic signal at room temperature. Interestingly, temperature dependent magnetization showed a su-perparamagnetic behavior with a blocked state in the low temperature range. The Co doped ZnO samples evidenced a weak ferromagnetic signal and a paramagnetic com-ponent, which increased with x. The saturation magnetization increased until x=0.03 and then decreased for x=0.05, while the coercive field gradually decreased.