Quasiparticles relaxation processes in Nb/CuNi bilayers

The dynamic instability of the moving vortex lattice at high driving currents has been studied in superconductor (S)/weak ferromagnet (F) bilayer, Nb/Cu0.38Ni0.62. Voltage-current, V(I), characteristics have been acquired as a function of both the temperature, T, and the magnetic field, H, and interpreted in the framework of the model proposed by Larkin and Ovchinnikov. From these analysis the values of the quasiparticle relaxation time, τE, have been estimated. The results confirm the high performance of S/F hybrids in terms of velocity in the energy relaxation process, compared to corresponding single superconducting thin films. Moreover the temperature dependence of τE is extremely smooth, also if compared with the data reported in literature for other weak ferromagnet S/F based systems. This last result has been tentatively ascribed to the disorder present in the CuNi alloy