Depairing currents in the superconductor/ferromagnet proximity system Nb/Fe - art. no. 094506

We have investigated the behavior of the depairing current J(dp) in ferroma gnet/superconductor/ferromagnet (F/S/F) trilayers as function of the thickn ess 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 proximit y-effect model with two parameters (proximity strength and interface transp arency), which can also describe the dependence of the superconducting tran sition temperature T-c on d(s). We compare the computations with the experi mentally determined zero-field critical current J(c0) of small strips (typi cally 5-mum wide) 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 agreemen t with the expected behavior, which allows extrapolation to T=0. Both the a bsolute values of J(c0)(0) and the dependence on d(Nb) agree with the expec tations for the depairing current. We conclude that J(dp) is correctly dete rmined, notwithstanding the fact that the strip width is larger than both t he superconducting penetration depth and the superconducting coherence leng th, and that J(dp)(d(s)) is correctly described by the model.