Design of magnetic materials: the electronic structure of the ordered, doped Heusler compoundCo2Cr1−xFexAl

Abstract

The doped Heusler compoundsCo2Cr1−xFexAl with varyingCr to Fe ratio x were investigated experimentally and theoretically. The electronic structure of the ordered, doped Heuslercompound Co2Cr1−xFexAl (x = n/4,n = 0,1,2,3,4) was calculated using band structure calculations of different types. The orderedcompounds turned out to be ferromagnetic with the small Al magnetic moment alignedantiparallel to the 3d transition metal moments. All compounds show a gap around theFermi energy in the minority bands. The pure compounds exhibit an indirectminority gap, whereas the ordered, doped compounds exhibit a direct gap. Themagnetic circular dichroism in the x-ray absorption spectra was measured at theL2,3 edges of Co, Fe, and Cr of the pure compounds and thex = 0.4 alloy in order to determine element-specific magnetic moments. Calculations andmeasurements show an increase of the magnetic moments with increasing iron content.The experimentally observed reduction of the magnetic moment of Cr can beexplained by Co–Cr site disorder. The presence of the gap in the minority bands ofCo2CrAl can be attributed to the occurrence of pureCo2 and mixed CrAl(001)planes in the L 21 structure. It is retained in structures with different order of the CrAl planes but vanishes in theX structure with alternating CoCr and CoAl planes.