Co and Cu co-doped ZnO epitaxial films - A magnetically soft nano-composite

Abstract

A series of Co/Cu co-doped ZnO epitaxial films has been grown on sapphire substrates to investigate the possibilities of tailoring the magnetic properties in functional ZnO-Co/Cu nano-composites. The growth was performed using reactive magnetron sputtering varying the oxygen partial pressure to tune the incorporation of the dopants and the resulting valence state. At high oxygen pressures, Co2+ is formed and the resulting magnetic properties are very similar to phase pure paramagnetic Co-doped ZnO samples. However, the formation of a secondary CuO phase reduces the overall structural quality of the layers and virtually no substitutional incorporation of Cu2+ in ZnO could be evidenced. At low oxygen pressures, a significant fraction of metallic Co and Cu forming nanometer-sized superparamagnetic precipitates of a Co/Cu alloy can be evidenced which are embedded in a ZnO host matrix.