The proximity effect between a superconductor ͑S͒ and a weak ferromagnet ͑F͒ in sputtered Nb/ Pd 0.86 Ni 0.14 bilayers has been studied. The dependence of the critical temperature on the Sand F-layer thicknesses can be interpreted in the framework of recent theoretical models and yields reasonable numbers for the exchange energy of the ferromagnet and the interface transparency of the S/F barrier.

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We have studied the critical current density J c for onset of vortex motion and the dynamic instability of the moving vortex lattice at high driving currents in superconducting ͑S͒/ferromagnetic ͑F͒ Nb/ Ni 0.80 Fe 0.20 bilayers and in a single Nb film with the same thickness. The samples are all characterized by relatively high values of the pinning strength. The measured current-voltage characteristics are successfully described in the framework of the Larkin-Ovchinnikov model, modified in order to take into account the effect of the pinning close to the instability. We find that J c is smaller in the S/F bilayers than in the single film and argue that this is due to the strongly inhomogeneous order parameter in the bilayers. Also, the critical velocity v * for the occurrence of the instability is found to be significantly larger in the S/F bilayers than in the single S layer. By extracting the quasiparticle energy relaxation rate from v * , we show that this effect is due to the same inhomogeneous order parameter and the resulting lower average value of the superconducting gap.

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