Static and dynamic properties of the vortex lattice in superconductor/weak ferromagnet bilayers

By measuring I-V characteristics as a function of the temperature and the external magnetic field, we have analyzed the static and dynamic properties of the vortex lattice in Nb/Pd 0 . 84 Ni 0 . 16 bilayers. In particular, the critical current density J c for the onset of the vortex motion and the dynamic instability of the moving vortex lattice at high driving currents have been studied and compared to the results obtained in a single Nb film. We find that J c is smaller in the bilayers than in the single superconducting film due to the smaller value of the superconducting order parameter in the bilayers. The critical velocity v * for the occurrence of the instability is larger in the S/F bilayers than in the single S layer. However, the quasiparticle energy relaxation rate extracted from v * is almost temperature-independent, implying that a different relaxation mechanism plays a role in the Nb/Pd 0 . 84 Ni 0 . 16 bilayers.