Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 18: Poster I : Bio Magn. (1-2); Mag.Imgaging (3-9); Magn. Semiconductors (10-16); Half Metals & Oxides (17-20); Coupl.Phenomena (21-27); Magn. Mat. (28-41); Micro & Nanostr. Magn. Materials (42-61); Micro Magn. (62-64); Surface Magnetism (65-70); Transport Phenomena (71-85)

MA 18.84: Poster

Dienstag, 26. Februar 2008, 15:15–18:30, Poster E

An investigation of bcc-Co thin-film and bulk properties and their influence on tunneling magnetoresistance — •Marjana Ležaić, Frank Matthes, Phivos Mavropoulos, Stefan Blügel, and Claus M. Schneider — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany

We report on the electronic band structure modifications of metastable bcc Co films introduced by tetragonal distortion of the lattice along the [001] direction. Density functional calculations were performed to find the equilibrium lattice distortion and the resulting electronic structure, predicting, for individual bands, a shift in binding energy dependent on the sign and size of the tetragonal distortion. Under certain tetragonalisation, a minority band with Δ₁ symmetry along Γ−X shifts to lower energies and intersects the Fermi level. The effect can severely reduce the tunneling magnetoresistance ratio (TMR) of Co/MgO/Co junctions. This is supported by spin-resolved photoemission spectroscopy measurements on bcc-Co thin films stabilized on bcc Fe. We also investigated, both theoretically and experimentally [1], the modification of the electronic structure of Co at the surface and interface to MgO. Furthermore, we calculated the influence of tetragonal distortion on exchange interactions and the Curie temperature of bcc Co, Fe and their alloys [2], as these quantities are related to the temperature stability of TMR in Co- and Fe-based junctions.
[1] L.-N. Tong et al., Phys. Rev. B 73, 214401 (2006).

[2] M. Ležaić et al., Appl. Phys. Lett. 90, 082504 (2007).