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.

Figure 1

(a) Top view of a $7\times 7\times 2$ GaN supercell having wurtzite structure. (b) ${\mathrm{Ga}}_{48}{\mathrm{N}}_{48}$ supercell which yields a nanowire of infinite length along $[0001]$ direction.

Figure 2

Six configurations of ${\mathrm{Ga}}_{46}{\mathrm{Mn}}_2{\mathrm{N}}_{48}$ supercell identifying various Ga sites that have been replaced by Mn. The lighter spheres are N, the gray spheres are Ga, and the black spheres are Mn.

Figure 3

(a) Total DOS corresponding to pure nanowire ${\mathrm{Ga}}_{48}{\mathrm{N}}_{48}$ supercell, (b) total DOS of Mn-doped GaN nanowire, (c) partial spin DOS of Mn in ${\mathrm{Ga}}_{46}{\mathrm{Mn}}_2{\mathrm{N}}_{48}$, (d) partial spin DOS of Mn $3d$ and N $2p$ in ${\mathrm{Ga}}_{46}{\mathrm{Mn}}_2{\mathrm{N}}_{48}$.

Figure 4

Schematic representation of the ${\mathrm{Ga}}_{24}{\mathrm{N}}_{24}$ supercell. The lighter spheres are Ga and the darker spheres are N. The atoms occupying sites marked 0 and 1 are along $[10\overline{1}0]$ direction and these occupying positions 3 and 0 are along $[0001]$ direction.