Effect of Mn concentration and growth temperature on nanostructures and magnetic properties of Ge_1-xMn_x grown on Si

The nanostructures and magnetic properties of Ge_1-xMn _x thin films grown on Si substrates by molecular beam epitaxy, with different nominal Mn concentrations (1-4%) and different growth temperatures, have been systematically investigated by transmission electron microscopy and superconducting quantum interference device. It was discovered that when Ge _1-xMn_x thin films were grown at 70 °C, with increase in Mn concentration, Mn-rich tadpole shaped clusters started to nucleate at 1% Mn and become dominate in the entire film at 4% Mn. While for the thin films grown at 150 °C, tadpoles was firstly seen in the film with 1% Mn and subsequently Mn-rich secondary precipitates became dominant. The magnetic properties show specific features, which are mainly related to the nature and amount of Mn-rich clusters/precipitates within these thin films.