We fabricated high quality \Nb/\Al2\O3/\Ni0.6\Cu0.4/\Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Depending on the thickness of the ferromagnetic \Ni0.6\Cu0.4 layer and on the ambient temperature, the junctions were in the 0 or π ground state. All junctions have homogeneous interfaces showing almost perfect Fraunhofer patterns. The \Al2\O3 tunnel barrier allows to achieve rather low damping, which is desired for many experiments especially in the quantum domain. The McCumber parameter βc increases exponentially with decreasing temperature and reaches βc≈700 at T=2.1K. The critical current density in the π state was up to 5A/cm2 at T=2.1K, resulting in a Josephson penetration depth λJ as low as 160μm. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the \Ni0.6\Cu0.4 layer and different transparencies of the interfaces.
@article{arxiv.cond-mat/0604097,
title = {High quality ferromagnetic 0 and pi Josephson tunnel junctions},
author = {M. Weides and M. Kemmler and H. Kohlstedt and A. Buzdin and E. Goldobin and D. Koelle and R. Kleiner},
journal= {arXiv preprint arXiv:cond-mat/0604097},
year = {2007}
}