C. Cirillo

Interface transparency and proximity effect in Nb/Cu triple layers realized by sputtering and molecular beam epitaxy

We have investigated, in the framework of the proximity effect theory, the interface transparency T between Nb and Cu in the case of high quality Nb/Cu trilayers fabricated by molecular beam epitaxy (MBE) and sputtering deposition techniques. The obtained T values do not seem to be strongly influenced by the fabrication methods but more by the intrinsic properties of the two metals; a slightly higher value for T has even been deduced for the MBE prepared samples. The proximity effect in these samples has also been studied in the presence of an external magnetic field. In the parallel configuration a significant shift towards lower values of the 2D–3D crossover temperature has been observed for MBE samples, in good agreement with very recent theoretical predictions. In the perpendicular case a positive curvature of the temperature dependence of the upper critical field has been detected, which was less pronounced for sputtered samples. Both the effects have been observed only for trilayers with low Nb thickness (<600 A) which confirms the crucial influence of the interface transparency on the values of the upper critical field in such samples.

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 Jc 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 Jc 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/Pd0.84Ni0.16 bilayers.

New aspects of microwave properties of Nb in the mixed state

We present a study of the frequency dependence of the vortex dynamics in a conventional superconductor. We have employed a swept frequency, Corbino disk technique to investigate the temperature (3.6 K -T c ) and high-field (from H c2 /2 to H c2 ) microwave complex resistivity in Nb thin (20-40 nm) films as a function of the frequency (1-20 GHz). We have found several previously unnoticed features: (i) a field-dependent depinning frequency in the GHz range; (ii) deviations from the accepted frequency dependence [1], than can be ascribed to some kind of vortex creep; and (iii) the presence of switching phenomena, reminiscent of vortex instabilities. We discuss the possible origin of the features here reported.

Interface transparency of Nb/Pd layered systems

Abstract.We have investigated, in the framework of proximity effect theory, the interface transparency

Superconductor/Ferromagnet Hybrids: Bilayers and Spin Switching

{\cal T}

Magnetic field and temperature dependence of the critical vortex velocity in type-II superconducting films

of superconducting/normal metal layered systems which consist of Nb and high paramagnetic Pd deposited by dc magnetron sputtering. The obtained

Emergence of the stripe-domain phase in patterned permalloy films

{\cal T}

Vortex matching effects in Nb thin films due to Ni nanopillars embedded in anodic aluminum oxide substrates

value is relatively high, as expected by theoretical arguments. This leads to a large value of the ratio

Resistive transitions in Nb/Cu0.41Ni0.59/Nb trilayers

d_{s}^{cr}/ \xi_{s}

Long-range proximity effect in Nb-based heterostructures induced by a magnetically inhomogeneous permalloy layer

although Pd does not exhibit any magnetic ordering.