  We have used the Stern-Gerlach deflection technique to study magnetism in
chromium clusters of 20-133 atoms. Between 60 K and 100 K, we observe that
these clusters have large magnetic moments and respond superparamagnetically to
applied magnetic fields. Using superparamagnetic theory, we have determined the
moment per atom for each cluster size and find that it often far exceeds the
moment per atom present anywhere in the bulk antiferromagnetic lattice.
Remarkably, our cluster beam contains two magnetically distinguishable forms of
each cluster size with >= 34 atoms. We attribute this observation to structural
isomers.
