We have investigated the behavior of the depairing current $J_{\mathrm{dp}}$ in ferromagnet/superconductor/ferromagnet $\mathrm{}(F/S/F)\mathrm{}$ trilayers as function of the thickness $d_s$ of the superconducting layers. Theoretically, $J_{\mathrm{dp}}$ 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 transparency), 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 $J_{c0\mathrm{}}$ of small strips (typically $5-\mu \mathrm{m}$ wide) of Fe/Nb/Fe trilayers with varying thickness $d_{\mathrm{Nb}}$ of the Nb layer. Near $T_c$ the temperature dependence $J_{c0\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ is in good agreement with the expected behavior, which allows extrapolation to $T=0.\mathrm{}$ Both the absolute values of $J_{c0\mathrm{}}\mathrm{}\left(0\right)\mathrm{}$ and the dependence on $d_{\mathrm{Nb}}$ agree with the expectations for the depairing current. We conclude that $J_{\mathrm{dp}}$ 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 $J_{\mathrm{dp}}{(d}_s)$ is correctly described by the model.

• Received 10 January 2001

DOI:https://doi.org/10.1103/PhysRevB.64.094506