Gaining insights into the formation of high temperature GeMn nanocolumns: the effect of substrate crystalline orientation on their structural and magnetic properties

Thi Giang Le, Lisa Michez and Vinh Le Thanh

Abstract

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 °C, the Mn concentration of ~6% and the film thickness of ~80 nm. We found that due to the surfactant effect of Mn atoms, Ge_0,94Mn_0,06 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 Ge_0,94Mn_0,06 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.