We used transmission electron microscopy and magneto-optical Kerr effect measurements to investigate the chemical, structural, and magnetic properties of MnGe alloys fabricated by ion implantation of Mn+ at doses of 1× 10 16, 2× 10 16, and 4× 10 16 at.∕ cm 2 on Ge (100) single crystals at a substrate temperature of 300 C. Transmission electron microscopy images show the presence of Mn-rich clusters buried in a crystalline Ge matrix. These clusters are either Mn 5 Ge 3 crystallites (with mean diameters of 9.5 and 13.1 nm for the samples implanted at 2× 10 16 and 4× 10 16 at.∕ cm 2 doses, respectively) or in an amorphous phase (with average diameters of 4.3, 6.6, and 7.5 nm for the samples implanted at 1× 10 16, 2× 10 16, and 4× 10 16 at.∕ cm 2 doses, respectively). Chemical maps obtained by electron energy loss spectroscopy reveal also the presence of manganese diluted in the host Ge matrix. The …