  We present measurements of the current-phase relation (CPR) of
Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions as a
function of temperature. The CPR is determined by incorporating the junction
into a superconducting loop coupled to a dc SQUID, allowing measurement of the
junction phase difference. Junctions fabricated with a thin (~ 22 nm) barrier
of Cu0.47Ni0.53 sandwiched between Nb electrodes exhibit a re-entrant critical
current with temperature, vanishing at T =T_pi ~ 2-4 K. We find that the
critical current is negative for T < T_pi, indicating that the junction is a
pi-Josephson junction. We find no evidence for second-order Josephson tunneling
near T_pi in the CPR predicted by several theories.
