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(Color online) In-situ RHEED patterns of Fe3Si films of various thicknesses grown on GaAs(001) (left column), MgO(001) (middle column), and MgO(001) tunneling barrier (right column). The beam energy and the emission current were 15 keV and 30 μA, respectively. The incident plane of the electron beam was parallel to the  azimuthal direction with respect to the GaAs(001)-(4 × 6) reconstructed surface and along  of the MgO substrate.
(Color online) RT-CEM spectra of Fe3Si films with the 57Fe3Si tracer layer directly at the interface to GaAs(001) (sample A, (a)), to MgO(001) (sample B, (b)), and to a MgO tunneling barrier on GaAs(001) (sample C, (c)). The dots are the experimental data; the curve on top of the dots is a least-squares fit representing the sum of different magnetic sextets (six or nine subspectra, respectively) with Lorentzian line shape. Each subspectrum (as indicated to the right of each subspectra) originates from various crystallographic configurations of Si atoms around 57Fe on A or D sites of the Fe3Si lattice. The number of nn and nnn for Fe atoms results from the octahedral (max. nn = 8 Si atoms) and tetrahedral (max. nnn = 6 Si atoms) symmetries of the Fe3Si unit cell.
Probability (in %) for nn Si and nnn Si neighboring configurations around 57Fe atoms for sample B obtained by simulation following Arita et al. 17 Probabilities ≤ 0.1% were set to zero, including all configurations of nn = 0 and 1. For sample B (sample C), r A = 0.98(2) (0.98(2)), r B = 0.37(1) (0.37), and r D = 1.0 (1.0).
Calculated short-range (α 1 and α 2) and long-range order parameters S(B2) and S(D03) for samples B and C obtained from measured CEM spectra and Fe3Si lattice simulations using the method by Arita et al. 17 x R (Si), x(Si): calculated Si concentrations (at. %), following Refs. 15 and 17, respectively. The third row gives S(B2) = 0.63(2) as measured by x-ray diffraction assuming x(Si) = 17 at. %. The last row lists the parameters of the perfectly D03-ordered Fe3Si structure.
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