Figure 1.

(a) Magnetization curves of ZnO doped with various concentration of Cu from 0.05% to 10%. It is clear that undoped ZnO is diamagnetic. (b) Zero fields cooled and field cooled magnetization of 2% Cu-doped ZnO film indicate that Curie temperature of Cu-doped ZnO is well above the room temperature. (c) Variation of saturated magnetic moment per Cu²⁺ ion at different doping concentration measured at 300 K and 10 K. Connecting lines are guide for eyes. (d–e) X-ray photoelectron spectroscopy of 1% and 2.5% Cu-doped ZnO films, respectively. (f) Dependence of coercivity on Cu-content in ZnO. Connecting line is guide for eyes. Inset shows the magnified hysteresis loop of 0.05% and 10% Cu-doped ZnO from −0.5 kOe to 0.5 kOe.