Ferromagnetism in p-Type Manganese-Doped Zinc Oxide Quantum Dots

The magnetic exchange interactions between paramagnetic Mn2+ dopants in the presence of a N2– p-type defect in zinc oxide quantum dots are studied using density functional theory. Spin-dependent delocalization of the N2– 2p acceptor level among the nearest-neighbor Mn2+ dopants is observed. The calculations show that parallel Mn2+ spin alignment is favored upon the formation of a nitrogen-bridged Mn–Mn dimer. Although the effect is short-ranged, the observed magnitude of stabilization of the ferromagnetic alignment of nearest-neighbor Mn2+ spins arises from p–d exchange and suggests p-type Mn2+-doped ZnO quantum dots as excellent candidates for exhibiting room-temperature ferromagnetism. Analytical expressions are derived and supported by density functional theory calculations that show that the N2– concentration has a stronger influence on the magnetic splitting compared with that of the Mn2+ concentration.