  For a class of quasi-one-dimensional clusters, by using exact
diagonalization, we study the effect of side spins on the spin-spin
correlations on chain. Our calculations show that the side spins added in the
same sublattice can effectively strengthen the spin-spin correlations in large
distance region and make the change tend to flat. It is exactly proved that
periodically adding side spins can set up magnetic long-range orders in the
ground state. Also we investigate the effect of the density of side spins on
correlation strength. The case that two sublattices have different localized
spins is discussed.
