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Abstract:
The doped Hensler compounds CO2Cr1-xFexAl with varying Cr to Fe ratio x
were investigated experimentally and theoretically. The electronic
structure of the ordered, doped Heusler compound Co2Cr1-xFe Al (x = n/4,
n = 0, 1, 2, 3, 4) was calculated using band structure calculations of
different types. The ordered compounds turned out to be ferromagnetic
with the small Al magnetic moment aligned antiparallel to the 3d
transition metal moments. All compounds show a gap around the Fermi
energy in the minority bands. The pure compounds exhibit an indirect
minority gap, whereas the ordered, doped compounds exhibit a direct gap.
The magnetic circular dichroism in the x-ray absorption spectra was
measured at the L-2,L-3 edges of Co, Fe, and Cr of the pure compounds
and the x = 0.4 alloy in order to determine element-specific magnetic
moments. Calculations and measurements show an increase of the magnetic
moments with increasing iron content. The experimentally observed
reduction of the magnetic moment of Cr can be explained by Co-Cr site
disorder. The presence of the gap in the minority bands Of Co2CrAl can
be attributed to the occurrence of pure Co-2 and mixed CrAl(001) planes
in the L2(1) structure. It is retained in structures with different
order of the CrAl planes but vanishes in the X structure with
alternating CoCr and CoAl planes.
