  We report measurements of the critical current vs. Co thickness in
Nb/Cu/Co/Ru/Co/Cu/Nb Josephson junctions, where the inner Co/Ru/Co trilayer is
a "synthetic antiferromagnet" with the magnetizations of the two Co layers
coupled antiparallel to each other via the 0.6 nm-thick Ru layer. Due to the
antiparallel magnetization alignment, the net intrinsic magnetic flux in the
junction is nearly zero, and such junctions exhibit excellent Fraunhofer
patterns in the critical current vs. applied magnetic field, even with total Co
thicknesses as large as 23 nm. There are no apparent oscillations in the
critical current vs. Co thickness, consistent with theoretical expectations for
this situation. The critical current of the junctions decays over 4 orders of
magnitude as the total Co thickness increases from 3 to 23 nm. These junctions
may serve as useful templates for future explorations of spin-triplet
superconducting correlations, which are predicted to occur in supercon-
ducting/ferromagnetic hybrid systems in the presence of certain types of
magnetic inhomogeneity.
