Gaining Insights into the Formation of High Temperature GeMn Nanocolumns: the Effect of Substrate Crystalline Orientation on Their Structural and Magnetic Properties

Structural and magnetic characterisations along with first-principles total energy calculations based on the density functional theory have been combined to investigate the effects of (001) and (111)-oriented Ge substrates on the formation of GeMn nanocolumns. The samples were grown by means of molecular beam epitaxy (MBE) at the growth temperature (T-S) of 130 degrees C, the Mn concentration of similar to 6% and the film thickness of similar to 80 nm. We found that due to the surfactant effect of Mn atoms, Ge0,94Mn0,06 films grown on the Ge(001) substrate exhibit the nanocolumn structure along the growth direction and the Curie temperature (T-C) is higher than 400 K. On the other hand, for the Ge0,94Mn0,06 films grown on the Ge(111) substrate, Mn adatoms can easily diffuse into deeper layers through the interstitial sites, resulting in the formation of Ge3Mn5 streaks along the preferred direction [110] and surrounded by diluted matrix. The physical origin of the contrasting behaviour of Mn atoms is therefore strongly related to the different surface reconstruction.