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AM: Magnetismus

AM 11: Magnetowiderstand II

AM 11.1: Talk

Wednesday, March 28, 2001, 14:00–14:15, S 5.4

Electronic structure and transport properties of tunnel junctions. — •Michel Freyss, N. Papanikolaou, P.H. Dederichs, and R. Zeller — Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich

We present ab-initio calculations for the electronic structure and transport properties of epitaxial Fe / I / Fe (001) tunnel junctions, where I denotes an insulating or a semiconducting barrier. Tunnel junctions are widely studied for their spin-dependent transport properties and are good candidates for technological application as non-volatile magnetic random access memories (MRAM). The aim of our study is to correlate the conductance through the junction to its electronic structure. The electronic ground state properties are determined by the ab-initio screened KKR Green’s function method. For the transport properties we use a Green’s function formulation of the Landauer formalism. We focus on tunnel junctions with a semiconducting ZnSe barrier and compare them to junctions with Si, GaAs and MgO barriers. We comment on the presence of Metal-Induced Gap States in the semiconductor, the spin-polarization of which strongly depends on the nature of the barrier. We also present results for the magnetization profile, charge transfer and the q_∥-resolved local density of states, emphasizing on the role of interface states. The spin-dependent transport properties are calculated for varying thicknesses of the barrier. We show the important contribution of resonant states to the conductance for small barrier thicknesses, and the different characteristics of the conductance for majority and minority electrons which lead to tunnel magnetoresistance.