Magnetic and transport polaron percolation in diluted GeMn films

Abstract

Magnetic and electronic transport properties of Mn-doped Ge films have been studied as a function of Mn content. The films exhibit a long-range ferromagnetic behavior and a Mn dilution-dependent Curie temperature T C. Resistivity shows an insulator-like character with two distinct activation energies below about 80 K, while the Hall coefficient evidences a strong contribution from the anomalous Hall effect, in a p-type material. At a characteristic temperature T R, resistivity experiences a sudden reduction and the Hall coefficient reverses its sign from positive to negative. Moreover, around T R, any residual remanence and coercivity disappear. The transport and magnetic results are deeply related and can be qualitatively explained by a percolation model based on bound magnetic polarons due to localized holes in the GeMn alloy lattice.