  While achieving high Curie temperatures (above room temperature) in diluted
magnetic semiconductors remains a challenge in the case of well controlled
homogeneous alloys, several systems characterized by a strongly inhomogeneous
incorporation of the magnetic component appear as promising. Incorporation of
manganese into germanium drastically alters the growth conditions, and in
certain conditions of low temperature Molecular Beam Epitaxy it leads to the
formation of well organized nanocolumns of a Mn-rich material, with a
crystalline structure in epitaxial relationship with the Mn-poor germanium
matrix. A strong interaction between the Mn atoms in these nanocolums is
demonstrated by x-ray absorption spectroscopy, giving rise to a ferromagnetic
character as observed through magnetometry and x-ray magnetic circular
dichroism. Most interesting, intense magneto-transport features are observed on
the whole structure, which strongly depend on the magnetic configuration of the
nanocolumns.
