Enhanced ferromagnetic stability in Cu doped passivated GaN nanowires

Density functional calculations are performed to investigate the room temperature ferromagnetism in GaN:Cu nanowires (NWs). Our results indicate that two Cu dopants are most stable when they are near each other. Compared with bulk GaN:Cu, we find that magnetization and ferromagnetism in Cu doped NWs are strongly enhanced because the bandwidth of the Cu t d band is reduced because of the one-dimensional nature of the NW. The surface passivation is shown to be crucial to sustain the ferromagnetism in GaN:Cu NWs. These findings are in good agreement with experimental observations and indicate that ferromagnetism in this type of systems can be tuned by controlling the size or shape of the host materials.