  We study Superconductor-Ferromagnet-Superconductor (Nb-Cu0.47 Ni0.53-Nb)
Josephson junctions with spatial variations in the barrier thickness. Critical
current vs. magnetic flux diffraction patterns indicate that the critical
current density changes sign along the width of the junctions, creating
interfaces between 0 and pi junction regions around which spontaneous currents
can circulate. Shapiro steps observed at half-integer Josephson voltages can be
explained by the phase-locking of the spontaneous circulating currents to the
applied rf modulation.
