Room-temperature ferromagnetism in epitaxial p-type K-doped ZnO films

•Epitaxial K-doped ZnO films were deposited on c-Al2O3 substrates by RF-magnetron sputtering system.•A conversion of conductivity from n-type to p-type was observed with increasing the K concentration.•The effect of K-doping and annealing on the ferromagnetism of ZnO films were examined.•The origin of the ferromagnetism was discussed using first-principle calculations.

Room-temperature ferromagnetism with p-type conductivity was observed in epitaxial K-doped ZnO films prepared by RF-magnetron sputtering. The coincident changes in the electrical, optical and magnetic properties indicate that the cation holes play important roles in mediating the ferromagnetism in K-doped ZnO films. The maximum saturation magnetization of 8 emu/cm3 was obtained in the 8% K-doped film and the thermal annealing in air could stabilize the ferromagnetic signature. Finally, first-principle calculations reveal that the magnetic properties in K-doped ZnO films are attributed to the strong p–p interaction between the unpaired 2p electrons at O sites.