  We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE)
behaviour of a Haldane spin-chain compound containing light rare-earth ion,
Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H)
down to 2 K. In addition to the well-known long range antiferromagnetic order
setting in at (T_N=) 48 K as indicated in dc magnetization (M), we have
observed another magnetic transition near 10 K; this transition appears to be
of a glassy-type which vanishes with a marginal application of external
magnetic field (even H= 100 Oe). There are corresponding anomalies in
dielectric constant as well with variation of T. The isothermal M(H) curves at
2 and 5 K reveal the existence of a magnetic-field induced transition around 90
kOe; the isothermal H-dependent dielectric constant also tracks such a
metamagnetic transition. These results illustrate the MDE coupling in this
compound. Additionally, we observe a strong frequency dependence of a step in
T-dependent dielectric constant with this feature appearing around 25-30 K for
the lowest frequency of 1 kHz, far below T_N. This is attributed to interplay
between crystal-field effect and exchange interaction between Nd and Ni, which
establishes the sensitivity of dielectric measurements to detect such effects.
Interestingly enough, the observed dispersions of the T-dependent dielectric
constant curves is essentially H-independent in the entire T-range of
measurement, despite the existence of MDE coupling, which is in sharp contrast
with other heavy rare-earth members in this series.
