  The molecule-based magnet [Ru$_2$(O$_2$CMe)$_4$]$_3$[Cr(CN)$_6$] contains two
weakly-coupled, interpenetrating sublattices in a body-centered cubic
structure. Although the field-dependent magnetization indicates a metamagnetic
transition from an antiferromagnet to a paramagnet, the hysteresis loop also
exhibits a substantial magnetic remanance and coercive field uncharacteristic
of a typical metamagnet. We demonstrate that this material behaves like two
giant moments with a weak antiferromagnetic coupling and a large energy barrier
between the orientations of each moment. Because the sublattice moments only
weakly depend on field in the transition region, the magnetic correlation
length can be directly estimated from the magnetization.
