Transition-metal doped ZnO has attracted attention as a potential dilute magnetic semiconductor. Specifically, Co doped n-type ZnO has been theoretically predicted to show ferromagnetic properties above room temperature: a critical requirement for the achievement of spintronic devices. Currently, extensive experimental work is underway to verify these predictions, with Co doped ZnO being fabricated by conventional thin-film deposition techniques, such as pulsed laser deposition and molecular beam epitaxiy. More recently, synthesis of Co doped ZnO films by solution-based methods has become a popular alternative. In particular, synthesis with acetate precursors is being exploited as a method of cheaply and easily producing good quality polycrystalline ZnO powders and films. The appeal of this method is greatly enhanced due to the simplicity of the process and the ease of controlling the desired doping concentration. The reported structural and magnetic properties for the Co:ZnO system have, however, varied.
In this work, we present a comprehensive study of Co doped ZnO films produced using ethanolamine stabilised zinc and cobalt acetate precursors, with methoxyethanol as the solvent. The reactions and structural development in the range 100 - 1000°C were monitored by XRD, SEM, TEM-EDS and SQUID measurements in the doping range 0 - 20% Co. Mixed CoO-doped ZnO and Co-based spinel phases were detected with increasing Co concentration. Uniform nanostructured films were produced by spin-coating on Si and Al2O3 substrates. Evidence of a magnetically ordered state with a transition temperature well above 300 K was observed for certain preparation conditions. These results are also compared with a recently studied all-alkoxide based sol-gel route using zinc and cobalt methoxyethoxides in toluene-methoxyethanol solvent.
The results of this work significantly contribute towards understanding the Co:ZnO system produced by acetate synthesis.
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