We fabricated high quality Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with a step-like thickness, we obtain a 0-pi junction, with equal lengths and critical currents of 0 and pi parts. The ground state of our 330 microns (1.3 lambda_J) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-pi step and carrying ~6.7% of the magnetic flux quantum Phi_0. The dependence of the critical current on the applied magnetic field shows a clear minimum in the vicinity of zero field.
@article{arxiv.cond-mat/0605656,
title = {0-pi Josephson tunnel junctions with ferromagnetic barrier},
author = {M. Weides and M. Kemmler and E. Goldobin and H. Kohlstedt and R. Waser and D. Koelle and R. Kleiner},
journal= {arXiv preprint arXiv:cond-mat/0605656},
year = {2007}
}