Enhancement of ferromagnetic properties in Zn1−xCoxO by additional Cu doping

The high-temperature ferromagnetism in Co-doped ZnO samples fabricated by the standard solid-state reaction method is reported. Additional Cu doping into bulk Zn_0.98Co_0.02O is essential to achieve room-temperature ferromagnetism. Structure and composition analyses revealed that cobalt is incorporated into the lattice structure, forming a solid solution instead of precipitates. In the case of Zn_0.97Cu_0.01Co_0.02O, the coercive field measured by a vibrating sample magnetometer at room temperature is 60 Oe. The implication of the effect of Cu doping in bulk Zn_0.98Co_0.02O is also discussed.