Depairing currents in the superconductor/ferromagnet proximity system Nb/Fe

Abstract

We have investigated the behavior of the depairing current Jdp in ferromagnet/superconductor/ferromagnet (F/S/F) trilayers as function of the thickness ds of the superconducting layers. Theoretically, Jdp 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 transparency), which can also describe the dependence of the superconducting transition temperature Tc on ds. We compare the computations with the experimentally determined zero-field critical current Jc0 of small strips (typically 5−μm wide) of Fe/Nb/Fe trilayers with varying thickness dNb of the Nb layer. Near Tc the temperature dependence Jc0(T) is in good agreement with the expected behavior, which allows extrapolation to T=0. Both the absolute values of Jc0(0) and the dependence on dNb agree with the expectations for the depairing current. We conclude that Jdp 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 Jdp(ds) is correctly described by the model.

Source-reported materials — not catalogue approval

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