  Observation of ferroelectricity among non-d0 systems, which was believed for
a long time an unrealistic concept, led to various proposals for the mechanisms
to explain the same (i.e. magnetically induced ferroelectricity) during last
decade. Here, we provide support for ferroelectricity of a displacive-type
possibly involving magnetic ions due to short-range magnetic correlations
within a spin-chain, through the demonstration of magnetoelectric coupling in a
Haldane spin-chain compound Er2BaNiO5 well above its N\'eel temperature of
(TN=) 32K. There is a distinct evidence for electric polarization setting in
near 60 K around which there is an evidence for short-range magnetic
correlations from other experimental methods. Raman studies also establish a
softening of phonon modes in the same temperature (T) range and T-dependent
x-ray diffraction (XRD) patterns also reveal lattice parameters anomalies.
Density-functional theory based calculations establish a displacive component
(similar to d0-ness) as the root-cause of ferroelectricity from (magnetic) NiO6
chain, thereby offering a new route to search for similar materials near room
temperature to enable applications.
