Hard x-ray photoemission study of near-Heusler FexSi 1-x alloys

The structural and electronic properties of epitaxial and amorphous Fe _xSi_1-x alloys with x = 0.72 and 0.67 near the binary Heusler composition of x = 0.75 were determined using hard x-ray photoelectron spectroscopy (HXPS). By performing the measurements at a photon energy of 5950.3 eV, the bulk-sensitivity of the measurement is enhanced by a factor of 4-7 compared to conventional soft x-ray photoelectron spectroscopy at about 1000 keV. HXPS probes, on average, as far as 76 Å into the Fe _xSi_1-x samples. Via core-level spectra, it is found in the amorphous alloy that, in spite of the disordered structure that could lead to a broad distribution of chemical environments, the Si environment is mostly unique. Valence-band spectra reveal a clear distinction between the contributions of the two inequivalent Fe sites of the most highly ordered (x = 0.72, D0₃) epitaxial sample. The valence-band spectra are compared to results of fully relativistic coherent potential approximation calculations performed in the framework of the one-step model of photoemission, which reveal details of the atomic-orbital makeup of various features, and generally exhibit good agreement with experiment.