Ferromagnetic Co2FeSi Heusler alloys are potential candidates for semiconductor- ferromagnet hybrid structures acting as spin injectors (see also Core Research Area Ferromagnet-Semiconductor Hybrid Structures). Besides the basic requirement of structurally perfect and thermally stable hetero-interfaces, these intermetallic alloys have to crystallize in the ordered L21 phase to achieve half metallic behavior. Long-range order is however not necessarily perfect and the degree of perfection depends on growth conditions and generally diminishes with deviation from stoichiometry. Values of average long-range order ranging between 30% and 60% were measured in different Co2FeSi/GaAs samples by grazing-incidence X-ray diffraction using Synchrotron radiation. The order parameters are calculated from the ratio of integral intensities of the superlattice and the ratio of fundamental reflections taking into account the corresponding structure factors.
These results are correlated with information about the composition of the layers provided by electron energy-loss spectroscopy in the transmission electron microscope. The composition ratio of Fe/Co is measured in parallel to a line scan and lateral inhomogeneities are revealed with relative deviations from the average composition ratio up to 6.2%. The composition ratio fluctuates on a similar length scale as the intensity of the Co2FeSi 111 superlattice reflection. This finding indicates the influence of inhomogeneities in the stoichiometry on the local order of the lattice.