Surface dangling bonds dependent magnetic properties in Mn-doped GaAs nanowires

(Ga, Mn)As dilute magnetic semiconductor (DMS) is very promising for future spintronic devices, however, the lower Curie temperature ($T_c$) limits the applications. Here, using first-principles calculation based on density functional theory, we investigate the effect of the surface dangling bonds (SDBs) on the magnetic properties of Mn-doped GaAs nanowires (NWs). The results show that As (Ga)-SDBs are equivalent to holes (electrons) doping, giving rise to the magnetic moments on the surfaces of GaAs NWs. Further in the Mn-doped GaAs NWs, the SDBs can effectively regulate the total magnetic moments, due to charge transfers between the Mn-3d orbitals and the residual SDBs, which is analyzed by a carrier modulation model. Most importantly, the As-SDBs can stabilize the ferromagnetic (FM) states and enhance the $T_c$ in Mn-doped GaAs NWs because of their shallow acceptor level with lower energy compared with Mn-3d level.