Berlin 2005 – scientific programme
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MA: Magnetismus
MA 9: FV-internes Symposium "Heusler-Legierungen" (Organizers: B. Hillebrands, H. Zabel)
MA 9.1: Invited Talk
Friday, March 4, 2005, 15:15–15:45, TU EMH225
Halfmetallic Alloys: Electronic Structure, Magnetism, and Spin Polarisation — •Peter H. Dederichs, Iosif Galanakis, and Phivos Mavropoulos — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich
Halfmetallic alloys are ferromagnets which show a metallic behaviour for the majority electrons, but a semiconducting behaviour with a band gap at the Fermi level EF for the minority electrons. The resulting 100% spin polarisation at EF makes them of strong interest for spin electronics. Based on ab-initio calculations, we review the basic understanding of the electronic structure of half-metallic Heusler alloys. The origin of the gap is the d-d hybridisation between the lower-valent (magnetic) and the higher valent (non- magnetic) transition elements. Due to the band gap, an integer number of minority bands is occupied, so that an ideal Slater Pauling behaviour is obtained: The total moment M per unit cell scales with the total number Z of valence electrons, such that M=Z−18 for the half and M=Z−24 for the full Heusler alloys. We discuss the role of spin orbit coupling which in principle destroys the gap, but in practice is of minor importance, since the spin polarisation remains very high. Also other relativistic effects like orbital moments and magnetic anisotropy energies are typically very small. From application point of view the existence of disorder induced impurity gap states and of surface and interface states in the gap represent the biggest challenge. We shortly discuss the halfmetallic zincblende compounds like CrAs which show many similar properties.