Depairing currents in superconductor ferromagnet Nb/CuNi trilayers close to Tc

Abstract

In superconductor/ferromagnet (S/F) heterostructures, the exchange field h ex of the F-layer suppresses the superconducting order parameter in the S-layer via the proximity effect. One issue in current research is the effect of a domain state, or, more generally, different directions of h ex, on the superconductivity. We used a pulsed-current technique in order to measure the superconducting transport properties of Cu 1− x Ni x /Nb/Cu 1− x Ni x ( x=0.54) F/S/F trilayers structured in strips of about 2 μm wide and 20 μm long as function of a small in-plane magnetic field. We find that the depairing current is tied to the magnetization behavior. In particular, we show that the suppression of superconductivity in the S-layer is smallest when the external magnetic field equals the coercive field H c of the F-layers.