Carrier Concentration Effect of Cu-Doped ZnO Films for Room Temperature Ferromagnetism

Recent reports on the observation of room temperature ferromagnetism in Cu doped ZnO have been highly regarded by the scientific community. There are several contradicting reports where some authors have confirmed the occurrence of ferromagnetism in ZnO while others have ruled it out. Even in studies where room temperature ferromagnetism is reported, the effect of carrier type with the ferromagnetic properties is still unclear. To study this problem, the observation of room temperature ferromagnetism in Cu-doped (5%) single crystalline ZnO films grown on Si substrates was observed. ZnO films were prepared by pulsed laser deposition. Hall measurements showed that the Zn0.95Cu0.05O film was n-type with carrier density around 4.3×1017 cm-3. This film exhibits room-temperature ferromagnetism with a saturation magnetization of 0.31 µB/Cu atom. The predominant valence state of the doped Cu atoms is monovalent. When additional electrons were introduced into the films, the ferromagnetism was weaken and vanished. Our results confirm that the p-type nature of the film is not essential for realizing ferromagnetic characteristics, if only the concentration of n-type carriers were not very high.