We have studied the critical current density Jc for onset of vortex motion and the dynamic instability of the moving vortex lattice at high driving currents in superconducting (S)/ferromagnetic (F) Nb/Ni0.80Fe0.20 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 Jc 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.
High-velocity instabilities in the vortex lattice ofNb/Permalloy Bilayers
ATTANASIO, Carmine
2007-01-01
Abstract
We have studied the critical current density Jc for onset of vortex motion and the dynamic instability of the moving vortex lattice at high driving currents in superconducting (S)/ferromagnetic (F) Nb/Ni0.80Fe0.20 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 Jc 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.