Accurate ab initio full-potential augmented plane wave (FLAPW) electronic calculations within density functional theory in both local density and generalized gradient approximations have been performed for ${\mathrm{Mn}}_x{\mathrm{Ge}}_{1-x}$ and ${\mathrm{Mn}}_x{\mathrm{Si}}_{1-x}$ ordered alloys, focusing on their electronic and magnetic properties as a function of the host semiconducting matrix (i.e., Si vs Ge), the Mn concentration, and the spin magnetic alignment (i.e., ferromagnetic vs antiferromagnetic). As expected, Mn is found to be a source of holes and localized magnetic moments of about $3{\mu }_B/\mathrm{Mn}.$ The results show that irrespective of the Mn content, the Ge-based systems are very close to half-metallicity, whereas the Si-based structures just miss the half-metallic behavior due to the crossing of the Fermi level by the lowest conduction bands. Moreover, the ferromagnetic alignment is favored compared to the antiferromagnetic one, with its stabilization generally increasing with Mn content; this is in agreement with recent experimental findings for MnGe systems and supports the view that this class of ferromagnetic semiconductors constitute basic spintronic materials.

• Received 23 December 2002

DOI:https://doi.org/10.1103/PhysRevB.68.155203