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/Pd0.84Ni0.16 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 upsilon* 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 upsilon* is almost temperature-independent, implying that a different relaxation mechanism plays a role in the Nb/Pd0.84Ni0.16 bilayers.