Nb-PtNi-Nb Josephson junctions made by 3D FIB nano-sculpturing

We use Focused Ion Beam (FIB) for fabrication of nano-scale Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions, aiming to achieve a uniform, mono-domain state in the F-layer within the junction. We employ a Pt1-xNix alloy, characterized by the perfect solubility of the two components, for obtaining a homogeneous diluted ferromagnet. We perform a systematic analysis of both chemical composition, and ferromagnetic properties of Pt1-xNix thin films for different Ni-concentrations. The nano-scale homogeneity of the Pt1-xNix films is confirmed by energy dispersive X-ray spectroscopy. The Curie temperature of Pt1-xNix films decreases in a non-linear manner with Ni concentration. We observe that the critical current density of Nb - Pt1-xNix - Nb junctions decreases non-monotonously with increasing Ni-concentration: at x ∼ 30% it exhibits a minimum, which we attribute to switching into the π state as a function of Ni-concentration.