Room-temperature ferromagnetism induced by Cu vacancies in Cu_x(Cu₂O)_1-x granular films

Cu_x(Cu₂O)_1-x (0.09≤Cux≤1.00) granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cu_x(Cu₂O)_1-x deposition. Room-temperature ferromagnetism (FM) is found in all of the samples. The saturated magnetization increases at first and then decreases with the decrease of x. The photoluminescence spectra show that the magnetization is closely correlated with the Cu vacancies in the Cu_x(Cu₂O)_1-x granular films. Fundamentally, the FM could be understood by the Stoner model based on the charge transfer mechanism. These results may provide solid evidence and physical insights on the origin of FM in the Cu₂O-based oxides diluted magnetic semiconductors, especially for systems without intentional magnetic atom doping.