2007/05/04 by Thibaut Devillers, Matthieu Jamet, A. Barski +11
Chemistry · Engineering · Materials Science · Physics and Astronomy · #Analytical Chemistry (journal) #Chemistry #Condensed matter physics #Crystallography #Magnetism #Magneto-Optical Properties and Applications #Materials science #Nanoclusters #Nanotechnology #Paramagnetism #Physics #Semiconductor Quantum Structures and Devices #ZnO doping and properties #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.76.205306
published as Physical Review B 76 (2007) 205306 · 10 pages 2 colonnes revTex formatted
arxiv created 2007/05/04 · openalex publication_date 2007/11/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report on the structural and magnetic properties of thin Ge_1\ensuremath-xMnx films grown by molecular beam epitaxy (MBE) on Ge(001) substrates at temperatures (Tg) ranging from 80 to 200\phantom\rule0.2em0ex\ifmmode^∘\else\textdegree\fiC, with average Mn content between 1% and 11%. Their crystalline structure, morphology, and composition have been investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy, and x-ray diffraction. In the whole range of growth temperatures and Mn concentrations, we observed the formation of manganese-rich nanostructures embedded in a nearly pure germanium matrix. The growth temperature mostly determines the structural properties of Mn-rich nanostructures. For low growth temperatures (below 120\phantom\rule0.2em0ex\ifmmode^∘\else\textdegree\fiC), we evidenced a two-dimensional spinodal decomposition resulting in the formation of vertical one-dimensional nanostructures (nanocolumns). Moreover, we show in this paper the influence of growth parameters (Tg and Mn content) on this decomposition, i.e., on the nanocolumn size and density. For temperatures higher than 180\phantom\rule0.2em0ex\ifmmode^∘\else\textdegree\fiC, we observed the formation of Ge3Mn5 clusters. For intermediate growth temperatures, nanocolumns and nanoclusters coexist. Combining high-resolution TEM and superconducting quantum interference device magnetometry, we could evidence at least four different magnetic phases in Ge_1\ensuremath-xMnx films: (i) paramagnetic diluted Mn atoms in the germanium matrix, (ii) superparamagnetic and ferromagnetic low-TC nanocolumns (120\ensuremath≤TC\ensuremath≤170\phantom\rule0.3em0exK), (iii) high-TC nanocolumns (TC\ensuremath≥400\phantom\rule0.3em0exK), and (iv) Ge3Mn5 clusters.