  We study the proximity effect in superconductor (S), antiferromagnetic (AF)
bilayers, and report the fabrication and measurement of the first trilayer
S/AF/S Josephson junctions. The disordered f.c.c. alloy \gamma-Fe50Mn50 was
used as the AF, and the S is Nb. Micron and sub-micron scale junctions were
measured, and the scaling of $J_C (d_AF)$ gives a coherence length in the AF of
2.4 nm, which correlates with the coherence length due to suppression of $T_C$
in the bilayer samples. The diffusion constant for FeMn was found to be 1.7
\times 10$^{-4}$ m$^2$ s$^-1$, and the density of states at the Fermi level was
also obtained. An exchange biased FeMn/Co bilayer confirms the AF nature of the
FeMn in this thickness regime.
