  We use quantum Monte Carlo simulations to study effects of free edges in the
two-dimensional spin-1/2 Heisenberg antiferromagnet. We find that the magnetic
response of an edge is smaller than the bulk susceptibility. This
counter-intuitive quantum effect can be traced to enhanced antiferromagnetic
nearest-neighbor spin correlations, i.e., tendency to local singlet formation,
at and close to the edge. These correlations form a comb-like pattern, which
can be reproduced with a simple variational valence-bond state. We also study
rough edges, and find that these instead significantly enhance the
susceptibility, due to local sublattice imbalance impeding singlet formation.
