Design of magnetic materials:: the electronic structure of the ordered, doped Heusler compound Co2Cr1-xFexAl

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.