Regensburg 2004 – wissenschaftliches Programm

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MA: Magnetismus

MA 8: Elektronentheorie

MA 8.5: Vortrag

Montag, 8. März 2004, 16:45–17:00, H22

The electronic structure of ordered and disordered, doped Heusler alloys: Co₂Cr_1−xFe_xAl — •H. C. Kandpal, G. H. Fecher, S. Wurmehl, H.-J. Elmers, G. Schönhense, and C. Felser — Johannes Gutenberg - Universität, 55099 Mainz

Doped Heusler alloys and compounds of the type Co₂Cr_1−xFe_xAl with varying Cr to Fe ratio x were investigated experimentally and theoretically. The electronic structure of the doped Heusler compound was calculated using different types of band structure calculations (FLAPW, LMTO, SPRKKR). The ordered compounds turned out to be ferrimagnetic with the Al magnetic moment being aligned anti-parallel to the 3d transition metal moments. Only the pure compound Co₂CrAl shows - in non-relativistic calculations - clearly a gap in the minority bands around the Fermi-energy. The ordered pure compounds exhibit an indirect minority gap, whereas the ordered, doped compounds exhibit a direct gap. Magnetic circular dichroism (MCD) in X-ray absorption was measured at the L_II,III 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 Co₂ and mixed CrAl (001)-planes in the L2₁ 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.