Enhancement of the magnetic anisotropy in single semiconductor nanowires via surface doping and adatom deposition

The magnetic anisotropy of single semiconductor (ZnO and GaN) nanowires incorporating both a transition metal (Co and Mn, respectively) as a substitutional surface dopant and a heavy metal (Au, Bi, or Pt) adatom is studied by performing density-functional supercell calculations with the HubbardUcorrection. It is found that a substantial enhancement in the magnetic anisotropy energy is obtained through the deposition of Bi; the deposition of Au and Pt leads to significant variation in other magnetic properties, but not in the magnetic anisotropy energy. An analysis within a band description shows that the coexistence of Bi adatom and a surface dopant with large spin moment activates a mechanism involving reorientation and readjustment of the spin moments of electrons in occupied bands in response to the change of magnetization direction, which promotes giant magnetic anisotropy. Our results for adsorption energetics indicate that the accommodation of Bi in the neighborhood of the surface dopant is more likely in GaN nanowires, because the Bi adatom does (not) tend to be closer to the Mn (Co) dopant on the surface of GaN (ZnO) nanowire. The stability of GaN nanowire with giant magnetic anisotropy owing to the incorporation of both Mn and Bi is demonstrated by performingab initiomolecular dynamics simulations at temperatures considerably higher than room temperature. These results suggest that adatom deposition and surface doping can be used complementarily to develop single nanowire-based spintronic devices.