High quality ferromagnetic 0 and pi Josephson tunnel junctions

We fabricated high quality $\text{Nb}\mathrm{/}{\text{Al}}_2{\text{O}}_3\mathrm{/}{\text{Ni}}_{0.6}{\text{Cu}}_{0.4}\mathrm{/}\text{Nb}$ superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Depending on the thickness of the ferromagnetic ${\text{Ni}}_{0.6}{\text{Cu}}_{0.4}$ layer and on the ambient temperature, the junctions were in the 0 or $\pi$ ground state. All junctions have homogeneous interfaces showing almost perfect Fraunhofer patterns. The ${\text{Al}}_2{\text{O}}_3$ tunnel barrier allows to achieve rather low damping, which is desired for many experiments especially in the quantum domain. The McCumber parameter ${\beta }_c$ increases exponentially with decreasing temperature and reaches ${\beta }_c\approx 700$ at $T=2.1\mathrm{K}$. The critical current density in the $\pi$ state was up to $5\mathrm{A}\mathrm{/}\mathrm{c}{\mathrm{m}}^2$ at $T=2.1 {\rm K}$,resultinginaJosephsonpenetrationdepth$\lambda_J$aslowas$160:\rm{\mu m}$. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the ${\text{Ni}}_{0.6}{\text{Cu}}_{0.4}$ layer and different transparencies of the interfaces.