Wideband microwave measurements in Nb/Pd$_{84}$Ni$_{16}$/Nb structures and comparison with thin Nb films

TL;DR

This study uses wideband microwave measurements to analyze vortex dynamics in Nb/PdNi/Nb heterostructures, revealing how the ferromagnetic layer influences flux-flow resistivity and pinning compared to pure Nb films.

Contribution

It demonstrates a method to directly measure flux-flow resistivity and vortex relaxation frequency in superconductor/ferromagnet heterostructures without critical current limitations.

Findings

F layer weakens vortex pinning

Flux-flow resistivity is enhanced by the ferromagnetic layer

Characteristic vortex relaxation frequency can be estimated without specific models

Abstract

We present wideband microwave measurements (1-22 GHz) taken on Superconductor/Ferromagnet heterostructures with the Corbino disk technique. We apply the technique to Nb/PdNi/Nb trilayers in the vortex state and we compare the results to data taken with the same technique on a Nb thin film. We show that it is possible to directly extract the genuine flux-flow resistivity from our frequency-dependent measurements without overcoming the (depinning) critical current. The characteristic frequency for vortex relaxation can also be estimated, without resorting to a specific model. We find that the F layer determines a weakening of pinning and an enhancement of the flux-flow resistivity with respect to the Nb film.