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Abstract:
Using circular dichroism in x-ray-absorption spectroscopy (XAS/XMCD), we
determined element-specific magnetic moments and spin-resolved
unoccupied densities of states (DOS) for Co, Fe, and Mn in the
quaternary Heusler compounds CoFeMnZ (Z = Al, Ga; Si, Ge). These
compounds belong to a class of highly spin-polarized materials with
cubic LiMgPdSn-type structure. Different structure models for the
sublattice occupation leading to similar average magnetization values
can be distinguished by comparison of element-specific moments with
theory. We find that the compounds form similar structures, where Co,
Fe, Mn, and Z occupy the X, X', Y, and Z sublattice of the related
X(2)YZ L2(1)-Heusler structure, for which half-metallic behavior was
predicted. The unoccupied partial DOS as derived from the XAS/XMCD
spectra for Co, Fe, and Mn are compared to theoretical results. A good
agreement is found for Co and Fe, while Mn spectra reveal additional
final-state effects (multiplets).
