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.