Dilution of Mn in Ge: the evidence from samples’ electrical and magneto-transport properties

The investigation of Mn in Ge was motivated by its potential application as spintronics material. Recently various groups realized that two phases of Mn in Ge:Mn, prepared by ion implantation and MBE [1], coexist: diluted Mn ions and a Mn-rich secondary phase. Usually the Mn-rich secondary phase is believed to be responsible for the observed ferromagnetism. In this contribution, we provide direct evidence for the dilution of Mn in Ge by electrical and magneto-transport investigation. Mn ions were implanted into semi-insulating Ge wafers. We observed p-type conductivity in the implanted surface layer with the thermal activation energy similar to that of heavily doped Ge [2]. The observed anomalous Hall effect (AHE) cannot be explained by the presence of Mn5Ge3 clusters, since the AHE does not mimic the hysteresis of magnetic moments probed by SQUID. We propose that the dilution of Mn in Ge results in a large spin-splitting of the valence band, however the concentration of diluted Mn is not large enough to develop ferromagnetic coupling. [1] Appl. Phys. Lett. 88, 061907 (2006); Phys. Rev. B 77, 045203 (2008). [2] Phys. Rev. 100, 659 (1955), Phys. Rev. Lett. 91, 177203 (2003).