Ferromagnetism and carrier confinement in Mn/Ge digital alloys - art. no. 035210

Ab initio electronic structure calculations within density functional theory have been performed for digital layers of Mn in Ge, focusing on the electronic and magnetic properties as a function of the Mn concentration and Ge spacer thickness. We find that all the structures show ferromagnetic alignment as the most favored and an electronic structure very close to half metallicity. The structures with two Mn monolayers bridged by one Ge spacer layer are found to be the most stable, indicating that a high local Mn concentration might be obtained in nonequilibrium conditions. As the number of Ge spacer layers is increased, the magnetic coupling between neighboring Mn layers decreases vanishing at spacings larger than five Ge monolayers, and this is seen to match the spatial extension of the hole induced on the Ge sites by Mn doping. Finally, we discuss the carrier and spin-density localization and show that, while majority spins are well localized in regions close to the Mn-doped planes, carriers extend on quite wider regions.