Magnetic Properties of Cu Nanoclusters Embedded in ZnO Thin Films

Cu nonmagnetic metallic nanoclusters were embedded in the ZnO thin film by using nanocluster beam deposition. No presence of secondary phase was detected in X-ray diffraction (XRD) analysis, but secondary phases CuO and Cu₂O nanoclusters were detected in films by transmission electron microscopy (TEM). Cu nanoclusters embedded in ZnO films have the average particle size around 8-10 nm. Cu atoms were surrounded by ZnO matrix, and the interface effect caused overlapping of p-orbital from O contributed by ZnO and d-orbital contributed by Cu as suggested by XPS and UV-Vis absorbance results. Alternating gradient field magnetometer (AGM) results show that the embedment of nonmagnetic Cu nanoclusters in ferromagnetic ZnO thin films can enhance the room temperature ferromagnetism of ZnO thin film up to maximum Ms = 2.64 emu/cc with small coercivities lower than 70 Oe. The saturation magnetization (Ms) value increases with Cu volume fraction in ZnO and decreases with Cu volume fraction after certain volume fractions of Cu were achieved. Based on the clues given by XPS results, +1 valence state of Cu is in the ferromagnetism favorable state, indicating possible spin polarization occurred and ferromagnetism induced in the system.