Modulated spinodal decomposition in (Ge,Mn) films grown on GaAs(001)

The field of ferromagnetic semiconductors evolves very fast nowadays for their potential use in spintronic devices. Up to now, efforts have mainly focused on Diluted Magnetic Semiconductors but Curie temperatures in these materials still remain modest. One possible route to increase at least locally transition temperatures is to use spinodal decomposition leading to transition metal-rich high T$_{C}$ nanostructures. We focus here on (Ge,Mn) considered as a model system for spinodal decomposition and compatible with Si-based microelectronics. While the growth of (Ge,Mn) films on Ge substrates leads systematically to Mn-rich self-assembled nanocolumns exhibiting high T$_{C}$, we demonstrate the fine control of spinodal decomposition in (Ge,Mn) films grown on GaAs. Using different surface preparations, we clearly identify the role of surface morphology and impurity diffusion from the substrate (Ga or As) on the nanocolumns growth and the electrical properties (MR and AHE).