Mn-doped ZnO and (Mn, Cu)-doped ZnO thin films: Does the Cu doping indeed play a key role in tuning the ferromagnetism?

Zn_Mn_O and Zn_Mn_Cu_O thin films were grown by the pulsed laser deposition technique on R-cut Al_2O_3 substrates under various conditions. Both Zn_Mn_O and Zn_Mn_Cu_O films that were fabricated at 650 °C under an oxygen pressure of 0.1 Torr show ferromagnetism (FM) above room temperature. It appears that by applying appropriate conditions, doping Mn alone can induce FM in ZnO itself, while co-doping with Cu might enhance the magnetic moment for some extent in some specific cases, but not very crucially as theories have predicted. Growth conditions likely play more important roles to result in ferromagnetic samples