Zn vacancy induced ferromagnetism in K doped ZnO

Using first-principle calculations, we studied the mechanism of the magnetic properties of K doped ZnO. The results show that the magnetic moment originates from the O 2p hole states around Zn vacancies. K substitution in Zn can also induce magnetism, which is due to the formation of the partial Zn vacancy induced by lattice distortion. Ferromagnetic ordering occurs via p-p coupling, which is mediated by the holes that result from K doping. Further investigation indicates that a single Zn vacancy has a high formation energy, whereas the formation energy of a defect complex composed of K interstitial (K_int), K substitutional (K_Zn) and zinc vacancy (V_Zn) is significantly reduced. In addition, K dopants prefer a large separation, which suggests uniform distribution. Experimentally, K doped ZnO nanorods were fabricated using a hydrothermal method and room temperature ferromagnetism was observed. 2 at% K doped ZnO has the largest saturation magnetization, which is consistent with first-principle calculations.