Core-shell nanostructure in a Ge0.9Mn0.1 film observed via structural and magnetic measurements

Manganese-doped germanium films are model systems for the study of nanospinodal decomposition into Mn-rich nanostructures and its influence on the electronic and magnetic properties. Here we study a film of Ge0.9Mn0.1 forming self-organized nanocolumns perpendicular to a Ge substrate with high resolution scanning transmission electron microscopy combined with electron energy loss spectroscopy, bulk magnetization, and muon spin rotation and relaxation (mu SR) measurements. The Mn-rich nanocolumns approximately form a triangular lattice with no detectable Mn atoms in the matrix. We find that they consist of cores surrounded by shells. The combined analysis of bulk magnetization and mu SR data enables us to characterize the electronic and magnetic properties of both the cores and shells. We argue that the discovered phase separation of the columns between a core and a shell is relevant for other transition-metal-doped semiconductors.