Local structural ordering in low-temperature-grown epitaxial Fe 3 + x Si 1 − x films on Ge(111)

For exploring group-IV semiconductor spintronics with ferromagnetic Heusler compounds, we study the local structural ordering of the stoichiometric Fe 3Si and off-stoichiometric Fe 3.2Si 0.8 films epitaxially grown on Ge(111) at a very low temperature of 130 ̂C. Analyzing their Fe57 Mössbauer spectra, we can discuss the site occupation of Fe atoms in the films grown directly on a semiconductor substrate, where the influence of the interfacial reactions between Fe 3Si or Fe 3.2Si 0.8 and Ge on the Mössbauer spectra is minimized. As a result, we can quantitatively obtain the local degree of the D0 3 ordering (∼67%) for the as-grown stoichiometric films, whereas we can not see the structural ordering for the as-grown off-stoichiometric films. Comparing the analytic data between as-grown and annealed films, we find that the postannealing can act effectively on the improvement of the structural ordering only for the off-stoichiometric films