Growth of ferromagnetic nanoparticles in a diluted magnetic semiconductor obtained by Mn+ implantation on Ge single crystals

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 1x10(16), 2x10(16), and 4x10(16) at./cm(2) on Ge(100) single crystals at a substrate temperature of 300 degrees C. Transmission electron microscopy images show the presence of Mn-rich clusters buried in a crystalline Ge matrix. These clusters are either Mn5Ge3 crystallites (with mean diameters of 9.5 and 13.1 nm for the samples implanted at 2x10(16) and 4x10(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 1x10(16), 2x10(16), and 4x10(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 samples with higher doses are ferromagnetic with the Curie temperature approaching 270 K. The sample implanted at the 1x10(16) at./cm(2) dose exhibits ferromagnetic hysteresis only at 5 K.