Combined effects of electron doping and surface polarity on the ferromagnetism in Gd implanted polar ZnO wafers

Abstract

The microstructural, electrical and magnetic properties of Gd-doped and (Al, Gd) codoped Zn-polar and O-polar ZnO wafers manufactured by the ion implantation method are systematically and comparatively investigated. We report an intrinsic ferromagnetic behaviour of Gd-implanted polar ZnO wafers enhanced by Al codoping. It was found that the saturation magnetization for the doped O-polar ZnO wafer is stronger than that of the implanted Zn-polar ZnO wafer. The introduction of Al ions into Gd-implanted polar ZnO enables a further improvement in the ferromagnetism that is directly relevant to the carrier concentration. This finding suggests that the carrier-mediated exchange mechanism may account for the establishment of the long-range ferromagnetic order in the doped ZnO wafers. First-principles calculations confirm that the interaction between the Gd-4 f state and the O-2p state is stronger in oxygen polar ZnO, producing a higher magnetic moment. The increase in the magnetic moment of (Al, Gd) co-implanted ZnO is mainly derived from hybridization of the Al and O orbitals. Our results confirm that larger ferromagnetism can be obtained in Gd-doped O-polar ZnO wafers and that the magnetization can be effectively improved by controlling the electron doping concentration, which highlights the viability of developing spintronic devices based on polar ZnO by codoping magnetic ions and group Ⅲ elements.