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Title: Structural and chemical ordering of Heusler Co xMn yGe z epitaxial films on Ge (111). Quantitative study using traditional and anomalous x-ray diffraction techniques

We found that epitaxial films of Co xMn yGe z grown on Ge (111) substrates by molecular-beam-epitaxy techniques have been investigated as a continuous function of composition using combinatorial synchrotron x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy techniques. A high-resolution ternary epitaxial phase diagram is obtained, revealing a small number of structural phases stabilized over large compositional regions. Ordering of the constituent elements in the compositional region near the full Heusler alloy Co 2MnGe has been examined in detail using both traditional XRD and a new multiple-edge anomalous diffraction (MEAD) technique. Multiple-edge anomalous diffraction involves analyzing the energy dependence of multiple reflections across each constituent absorption edge in order to detect and quantify the elemental distribution of occupation in specific lattice sites. Results of this paper show that structural and chemical ordering are very sensitive to the Co : Mn atomic ratio, such that the ordering is the highest at an atomic ratio of 2 but significantly reduced even a few percent off this ratio. The in-plane lattice is nearly coherent with that of the Ge substrate, while the approximately 2% lattice mismatch is accommodated by the out-of-plane tetragonal strain. Furthermore, the quantitative MEAD analysis reveals no detectable amountmore » (<0.5%) of Co-Mn site swapping, but instead high levels (26%) of Mn-Ge site swapping. Increasing Ge concentration above the Heusler stoichiometry (Co 0.5 Mn 0.25 Ge 0.25 ) is shown to correlate with increased lattice vacancies, antisites, and stacking faults, but reduced lattice relaxation. The highest degree of chemical ordering is observed off the Heusler stoichiometry with a Ge enrichment of 5 at.%.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [1]
  1. Univ. of North Carolina, Chapel Hill, NC (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1098-0121; R&D Project: LS001
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 92; Journal Issue: 22; Journal ID: ISSN 1098-0121
American Physical Society (APS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
OSTI Identifier: