Ferromagnetism in Mn-Doped GaN Nanowires

Using density functional theory we show that the magnetic coupling of Mn atoms in the nanowires, unlike that in the thin film, is ferromagnetic. This ferromagnetic coupling, brought about due to the confinement of electrons in the radial direction and the curvature of the Mn-doped GaN nanowires’ surface, is mediated by N as is evidenced from the overlap between Mn $3d$ and N $2p$ states. Calculations of the anisotropic energy further show that the magnetic moment orients preferably along the $[10\overline{1}0]$ direction while the wire axis points along the $[0001]$ direction.