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TT: Fachverband Tiefe Temperaturen

TT 28: Transport - Poster Session

TT 28.40: Poster

Donnerstag, 29. März 2007, 14:00–17:45, Poster A

Spin-polarized tunneling currents through magnetic layer systems — •Niko Sandschneider and Wolfgang Nolting — Humboldt-Universität zu Berlin, Institut für Physik, Newtonstr. 15, 12489 Berlin, Germany

Using the Keldysh formalism we calculate the tunneling currents through a hybrid structure where a confined magnetic insulator (I) is sandwiched between two leads. They can be either normal metals (M) or superconductors(S) (M/I/M, M/I/S, S/I/S). The insulator is assumed to have localized moments which can interact with the tunneling electrons. This is described by the Kondo lattice model (KLM) and treated within an interpolating self-energy approach. For the superconductor we used the mean-field BCS theory. We also propose an effective medium approximation for the M/I/S and S/I/S systems.

By deriving a current formula it is possible to calculate the voltage-dependent tunneling current in a self-consistent way. It is shown that the current is always spin-polarized and that the degree of polarization depends on the applied voltage and the parameters of the materials. In M/I/M systems it is not possible to get a spin polarization high enough for technological applications.

The experimental results of [1] can be reproduced qualitatively. It is also possible to determine optimal parameters for high spin polarization in the systems under consideration.

[1] X. Hao, J.S. Moodera and R. Meservey, Phys. Rev. B 42, 8235 (1990)