Room temperature ferromagnetic semiconductors, compatible with the silicon technology is one of the major challenges in the spintronic research. In this work, we show that, grown by molecular beam epitaxy (MBE), Mn-doped Ge, with a mean manganese content of 6%, exhibits ferromagnetic ordering over 400K. Structural and chemical analyses performed using Transmission Electron Microscopy (TEM) and Energy Electron Loss Spectroscopy (EELS) revealed strong non-homogeneities of Mn distribution in our MBE grown GeMn samples. Growth process induces the segregation of Mn and formation of Mn rich nanocolumns surrounded by a nearly pure Ge matrix. The average diameter of nano-columns is 3 nm and the average distance between nanocolumns is about 10 nm. This indicates that the concentration of manganese in nanocolumns is about 30% which is an unknown phase of the GeMn into the binary phase diagram of GeMn. The magnetic properties of our GeMn films grown on Ge (001) were investigated with a superconducting quantum interference device (SQUID). Magnetization measurements revealed a Curie temperature higher than 400K. The zero-field cooled (ZFC) and field cooled (FC) SQUID investigations exclude the presence in our GeMn films of the GeMn clusters and of the known stables phases of GeMn: Ge₃Mn₅ or Ge₈Mn₁₁. Magneto-transport measurements evidence a pronounced anomalous Hall effect and confirm: (i) p-type character of our GeMn layers, and (ii) pronounced holes spin-polarization.

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