  Polarized and unpolarized neutron diffraction measurements have been carried
out to investigate the iron magnetic order in undoped NdOFeAs.
Antiferromagnetic order is observed below 141(6) K, which is in close proximity
to the structural distortion observed in this material. The magnetic structure
consists of chains of parallel spins that are arranged antiparallel between
chains, which is the same in-plane spin arrangement as observed in all the
other iron oxypnictide materials. Nearest-neighbor spins along the c-axis are
antiparallel like LaOFeAs. The ordered moment is 0.25(7) muB, which is the
smallest moment found so far in these systems.
