NiCu-based superconducting devices: Fabrication and characterization

The critical Josephson current (I_C) in superconducting/ ferromagnetic (S/F) multilayer-based junctions can be controlled by changing the relative directions of the magnetization in the F-layers. Recent experimental works [1, 2] show that an enhancement of I_C is achieved in S/F weak links when the alternating F-layers are antiparallel aligned. We present preliminary experimental results concerning the dependence of I_C on the relative orientation of the ferromagnetic layers in S/F₁/I/F ₂/S tunnel junctions where the F-layers are obtained by changing the relative composition of NiCu alloys. The multilayers were grown by electron beam deposition, and processed by Focused Ion Beam lithography. The magnetic state of the devices was directly determined by measuring the current perpendicular to plane (CPP) magnetoresistance (MR) at high bias. I_C was found to be larger when the F-layers are antiparallel aligned. The maximum change of I _C corresponds to the maximum change of MR. The application of a magnetic field induces a transition in the shape of the currentvoltage curve that seems to suggest Coulomb blockade effect. © 2006 IOP Publishing Ltd.