First-principles design of ferromagnetic nanostructures based on group-IV semiconductors

We perform first-principles density functional calculations for Mn doped group-IV (Ge, Si) based diluted magnetic semiconductors. It is found that the ferromagnetic spin configuration is stabilized when two Mn atoms are located along the direction in Ge and Si hosts due to the strong ferromagnetic exchange interaction between Mn impurities. Furthermore, our results show that a ferrimagnetic Mn cluster is more stable than the ferromagnetic Mn configuration along the direction, indicating that Mn impurities tend to gather and create undesired magnetic clusters in Ge and Si hosts. We conclude that the vicinal Ge( 111) and Si( 111) surfaces play an important role in the growth process of Mn doped Ge and Si in obtaining a ferromagnetically stable Mn configuration.