Interface-driven phase separation in multifunctional materials: The case of the ferromagnetic semiconductor GeMn.

We use extensive first-principles simulations to show the major role played by interfaces in the mechanism of
phase separation observed in semiconductor multifunctional materials. We make an analogy with the precipitation
sequence observed in oversaturated AlCu alloys, and replace the Guinier-Preston zones in this new context. A
class of materials, the
?
phases, is proposed to understand the formation of the coherent precipitates observed in
the GeMn system. The interplay between formation and interface energies is analyzed for these phases and for
the structures usually considered in the literature. The existence of the
?
phases is assessed with both theoretical
and experimental arguments.