  Crystals of the molecular magnet Mn12-acetate are known to contain a small
fraction of low- symmetry (minor) species with a small anisotropy barrier
against spin reversal. The lower barrier leads to faster magnetic relaxation
and lower coercive field. We exploit the low coercive fields of the minor
species to make a direct determination of the dipole field in Mn12-ac. We find
that the dipolar field of a fully magnetized crystal is 51.5 \pm 8.5 mT,
consistent with theoretical expectations.
