Unexpected ferromagnetism in n-type polycrystalline K-doped ZnO films prepared by RF-magnetron sputtering

The room temperature ferromagnetism in highly c-axis orientated K-doped ZnO polycrystalline films prepared by RF-magnetron sputtering were systematically investigated in this work. The decrease of n-type carriers and the enhanced acceptor-related photoluminescence with the K doping imply the formation of K substitution and Zn vacancy defects. It can be speculated that the room-temperature ferromagnetism observed in K-doped ZnO polycrystalline films is related with the hole. Since the saturation magnetization was positively dependent on the amount of hole defects based on the PL spectra analysis. The ferromagnetism coupling and the room temperature ferromagnetism obtained in K-doped ZnO polycrystalline films thus is originated from p–p coupling of the surrounding O atoms of the K substitution and Zn vacancy defects. The co-existing of both the n-type conductivity and the ferromagnetism induced by localized holes, which is much different from the previous report for epitaxial samples, give new insight into the behavior of d0 ferromagnetism in oxides.