  Electronic transport and magnetic properties of Ge1-xMnx/Ge(100) films are
investigated as a function of Mn dilution. Depending on x, characteristic
temperatures separate different regimes in both properties. Resistivity
exhibits an insulator-like behavior in the whole temperature range and, below
about 80 K, two distinct activation energies are observed. At a higher
temperature value, TR, resistivity experiences a sudden reduction. Hall
coefficient shows a strong contribution from the anomalous Hall effect and, at
TR, a sign inversion, from positive to negative, is recorded. The magnetic
properties, inferred from magneto-optical Kerr effect, evidence a progressive
decrease of the ferromagnetic long range order as the temperature is raised,
with a Curie temperature TC not far from TR. The transport and magnetic results
are qualitatively consistent with a percolation mechanism due to bound magnetic
polarons in a GeMn diluted magnetic semiconductor, with localized holes [A.
Kaminski and S. Das Sarma, Phys. Rev. B 68, 235210 (2003)].
