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MA: Magnetismus

MA 9: FV-internes Symposium "Heusler-Legierungen" (Organizers: B. Hillebrands, H. Zabel)

MA 9.2: Hauptvortrag

Freitag, 4. März 2005, 15:45–16:15, TU EMH225

The properties of Co₂Cr_1−xFe_xAl Heusler compounds — •Claudia Felser, Gerhard H. Fecher, Sabine Wurmehl, and Thomas Block — Johannes Gutenberg - Universität, 55099 Mainz, Germany

The compound Co₂Cr_0.6Fe_0.4Al was prepared, guided by striking features in the electronic structure of several magnetic Heusler compounds. Based on band structure calculations, this composition was chosen in order to obtain a ferromagnetic half metal with a van Hove singularity in the vicinity of the Fermi energy in the majority spin channel and a gap in the minority spin channel. The evidence for spinpolarized transport at room temperature was found, showing up in a magnetoresistive effect of 35% in a small magnetic field of 0.1 Tesla. Heusler compounds with composition Co₂Cr_1−xFe_xAl were prepared by arc melting and comprehensively characterized by means of XRD, SQUID magnetometry, Mößbauer spectroscopy, MXCD, ESCA and AES depth profiling. X-ray diffraction and EXAFS pointed on structural disorder phenomena. Band structure calculations are presented for ordered and disordered compounds. The connection between specific site disorder and the band structure is shown explicitly with particular emphasis on the half-metallic properties. Experimentally observed deviations from the ideal Heusler structure and from the simple Slater-Pauling rule for the magnetization are discussed in close relation to theoretical models.