Cr doped ZnO nanostructures: synthesis, electronic structures, and magnetic properties

In this experiment, we have attempted to dope Cr into ZnO nanostructure as a function of dopant concentration using sol-gel method, followed by controlled thermal annealing with some success. We have also examined the samples thus prepared with scanning electron microscopy (SEM), X-ray powder diffraction (XRD), near edge X-ray absorption fine structure (NEXAFS), both theoretical and experimental, and magnetic measurements. We found that low concentration of Cr can indeed be doped in ZnO and is substitutional, occupying the tetrahedral site. However, upon increasing dopant concentration and annealing temperature, a secondary phase with Cr occupying an octahedral site precipitates out, which was evident from SEM, XRD, and NEXAFS. Ferromagnetism at room temperature was not observed in any samples, although at low Cr concentration and 400 °C processing temperature, antiferromagnetism can be seen; however, at higher concentrations or processing temperatures, the samples show only paramagnetism.