  The direct growth of semiconductors over metals by molecular beam epitaxy is
a difficult task due to the large differences in crystallization energy between
these types of materials. This aspect is problematic in the context of
spintronics, where coherent spin-injection must proceed via ballistic transport
through sharp interfacial Schottky barriers. We report the realization of
single-crystalline ferromagnet/semiconductor/ferromagnet hybrid trilayers using
solid-phase epitaxy, with combinations of Fe3Si, Co2FeSi, and Ge. The slow
annealing of amorphous Ge over Fe3Si results in a crystalline filmlm identified
as FeGe2. When the annealing is performed over Co2FeSi, reflected high-energy
electron diffraction and X-ray diffraction indicate the creation of a different
crystalline Ge(Co,Fe,Si) compound, which also preserves growth orientation. It
was possible to observe independent magnetization switching of the
ferromagnetic layers in a Fe3Si/FeGe2/Co2FeSi sample, thanks to the different
coercive fields of the two metals and to the quality of the interfaces. This
result is a step towards the implementation of vertical spin-selective
transistor-like devices.
