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The morphology and composition of self organized manganese (Mn)-rich nanocolumns embedded in germanium (Ge) thin films were characterized at the atomic scale and in three dimensions with high resolution transmission electron microscopy and atom probe tomography. Experiments revealed Mn-enriched nano-columns of 3 nm in diameter with various morphologies. Their Mn-content was found smaller than that of the expected equilibrium phases and chemical fluctuations along the growth axis were additionally observed. By contrast, less than 0.05% of Mn was measured in the Ge-matrix. These results were correlated to the magnetic properties and allowed understanding the magnetic behavior of the nanocolumns. [ABSTRACT FROM AUTHOR]

In this letter, we study the structural and magnetic properties of Ge1-x-ySnxMny films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits a GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge1-x-ySnxMny layers is higher than in Ge1-xMnx films. This magnetic moment enhancement in Ge1-x-ySnxMny is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns. [ABSTRACT FROM AUTHOR]