Interface transparency of superconductor/ferromagnetic multilayersAarts, J.; Geers, J.M.E.; Bruck, E.H.; Golubov, A.A.; Coehoorn, R.; Olsovec, M. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We have investigated the behavior of the superconducting transition temperature T c in superconducting/ ferromagnetic ͑S/F͒ multilayers, as a function of the different layer thicknesses and for varying magnetic moment F of the F-layer atoms. The system studied consists of superconducting V and ferromagnetic V 1Ϫx Fe x alloys with x such that F on the Fe atom is varied between 2 and 0.25 B . We determined the superconducting coherence length in the F layer F , which is found to be inversely proportional to F . We also determined the critical thickness of the S layer, above which superconductivity appears. This thickness is found to be strongly nonmonotonic as function of the Fe concentration in the alloys. By analyzing the data in terms of the proximity-effect theory, we show that with increasing F , the increasing pair breaking in the F layer by the exchange field is counteracted by a decreasing transparency of the S/F interface for Cooper pairs.

We have investigated the behavior of the depairing current J dp in ferromagnet/superconductor/ferromagnet (F/S/F) trilayers as function of the thickness d s of the superconducting layers. Theoretically, J dp depends on the superconducting order parameter or the pair-density function, which is not homogeneous across the film due to the proximity effect. We use a proximity-effect model with two parameters ͑proximity strength and interface transparency͒, which can also describe the dependence of the superconducting transition temperature T c on d s . We compare the computations with the experimentally determined zero-field critical current J c0 of small strips ͑typically 5-m wide͒ of Fe/Nb/Fe trilayers with varying thickness d Nb of the Nb layer. Near T c the temperature dependence J c0 (T) is in good agreement with the expected behavior, which allows extrapolation to Tϭ0. Both the absolute values of J c0 (0) and the dependence on d Nb agree with the expectations for the depairing current. We conclude that J dp is correctly determined, notwithstanding the fact that the strip width is larger than both the superconducting penetration depth and the superconducting coherence length, and that J dp (d s ) is correctly described by the model.

We investigated ordering of the vortex lattice under the influence of a driving current in amorphous superconducting films of Nb 70 Ge 30 with varying amounts of disorder. Using the nonlinear behavior of the voltage versus current relations, i.e., the peak in the dynamical resistance, we map the occurrence of this dynamical ordering ͑DO͒ in the (B,T) phase diagram. Using the collective pinning analysis, DO is shown to appear when the size of the correlated regions drops below the order of Ϸ ten times the vortex lattice distance. This means that for weaker intrinsic disorder, DO moves closer to the melting line. The current at which DO occurs diverges at the melting transition, in agreement with the notion that increasing velocities are needed to overcome the effect of either temperature or softening of the shear modulus of the vortex lattice.

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