Electronic structure of quasi-crystalline AlMn in comparison with amorphous and crystalline alloys

Mixing of Al/Mn multilayers by xenon ions of 500 keV allows amorphous or single-phase quasicrystalline samples to be obtained for manganese concentrations below 20 at.% depending on the substrate temperature during the mixing; at higher manganese concentrations, complex crystalline phases are found.

The optical conductivity is determined from reflectance and/or ellipsometric measurements in the energy range from 0.5 to 6 eV and is shown to be very sensitive to the atomic structure. All spectra are strongly dominated by the manganese d states. No drastic differences are observed between the amorphous and the icosahedral states in samples with 19 at.% Mn. Differences found in samples with the global composition 10 at.% Mn are more probably due to the presence of an aluminium phase and to the changes in the density of states of the amorphous phase with manganese concentration.