  $R_2BaNiO_5$ ($R=$ rare earth) quasi-1-D antiferromagnets are structurally
equivalent to the well-studied 1-D S=1 Haldane-gap compound Y_2BaNiO_5. Unlike
the Y-nickelate though, these materials undergo 3-D magnetic ordering at finite
temperatures. Recent inelastic neutron scattering studies of Pr_2BaNiO_5 and
(Nd_{x}Y_{1-x})_2BaNiO_5 revealed purely 1-dimensional gap excitations that
propagate exclusively on the Ni-chains and are strikingly similar to Haldane
gap modes in Y_2BaNiO_5. In the ordered phase these excitations survive and
actually coexist with conventional spin waves. Below $T_{N}$ the gap energy
increases and scales as the square of the ordered moment on the Ni sites. The
results suggest that the Haldane singlet ground state of the Ni-chains is not
fully destroyed by N\'{e}el ordering.
