Inductive Critical Currents in Nb/Ni bilayers

We have carried out measurements of inductive critical currents in Nb/Ni bilayers. The films were grown by magnetron sputtering onto room temperature silicon substrates from separate sources. The bilayers were composed of an initial 33 nm Nb layer followed by a Ni layer, which was varied from 0-7 nm. Inductive critical currents were measured using a third harmonic technique at 1 kHz. $J_{c}$ varies as $(1-t)^{\gamma}$ with $\gamma$ being 3/2 as expected for pure Nb films, but decreasing as the Ni layer is increased (here $t$ is the reduced temperature, $T/T_{c}$). Our pure Nb film had a $T_{c}$ of 7.7 K with an inferred $J_{c}(0)$ of 61 MA/cm$^{2}$. As the Ni layer is increased, we see a marked reduction in the critical current which continues as the Ni layer is increased. Unlike the $T_{c}$'s for these samples, we do not see nonmonotonic behavior in the critical current, with $J_{c}(0)$ reducing to a constant value as Ni thickness goes beyond 3 nm.