Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 10: Superconductivity: Tunneling, Josephson Junctions, SQUIDs

TT 10.4: Talk

Monday, March 23, 2009, 14:45–15:00, HSZ 105

Josephson junctions with ferromagnetic Fe_0.75Co_0.25 and Cu₂MnAl interlayers — •Dirk Sprungmann¹, Kurt Westerholt¹, Hartmut Zabel¹, and Martin Weides² — ¹Institut für Experimentalphysik IV / Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany — ²IFF Forschungszentrum Jülich, D-52425 Jülich, Germany

We present our studies on SINFS Josephson junctions using Fe_0.75Co_0.25 and Cu₂MnAl-Heusler alloys for the F-layer. The junctions with Fe_0.75Co_0.25 represent the case of large magnetic exchange energies in the region of 500 meV. We show that these junctions exhibit an extremely short coherence length ξ_F1=0.16 nm and ξ_F2 = 0.54 nm and that the stray fields which emanate from the ferromagnetic layer cause increasing flux trapping effects for thicknesses d_F≥ 1.1 nm.
The opposite case with very small exchange energies in the region of several meV is realized in junctions with the Heusler alloy Cu₂MnAl. This alloy sputtered at room temperature features a distinct structural disorder which can be reduced by annealing. Because of the correlation between structural order and exchange energy the ferromagnetism can be fine tuned by thermal annealing. We study systematically the influence of the annealing process on the transport properties and correspondingly on the I_c(d_F)-characteristic of our junctions.
D. S., K. W. and H. Z. acknowledge financial support by SFB-491, and M. W. by project WE 4359/1-1.