Hole-induced ferromagnetic properties of Fe-added ZnO films

We investigated the structural and the magnetic properties of dilute magnetic semiconductor Zn_0.96Fe_0.04O films by using X-ray diffraction (XRD) and SQUID magnetization measurements. The films were synthesized on α-Al₂O₃ (0001) substrates by using a RF magnetron sputtering system with RF-powers of 40, 60 and 80 W. The XRD measurements revealed that the films had a wurtzite structure with their crystal (0001) directions oriented along the c-axis of the substrate. The best crystal quality was obtained at an RF-powder of 60 W. The SQUID magnetization measurements demonstrated that the films synthesized at 60 W were ferromagnetic at 10 K. An X-ray photoemission spectroscopy (XPS) analysis revealed an Fe chemical valence state of 2+ and energy dispersive spectroscopy measurements showed the presence of extra oxygen in the films. Our observations strongly suggest that Fe²⁺ ions are exactly substituted at the Zn²⁺ sites of the ZnO films and that the extra oxygen mediates the ferromagnetic properties of the films.