Displacive-type ferroelectricity from magnetic correlations within spin-chain

TL;DR

This study demonstrates displacive-type ferroelectricity driven by magnetic correlations in a spin-chain compound, supported by experimental evidence and DFT calculations, suggesting new avenues for room-temperature multiferroic materials.

Contribution

It provides experimental and theoretical evidence for magnetically induced displacive ferroelectricity in a non-d0 spin-chain compound, a novel mechanism in multiferroics.

Findings

Ferroelectricity observed above the Néel temperature due to short-range magnetic correlations.

Raman and XRD studies reveal lattice anomalies and phonon softening near 60 K.

DFT calculations indicate a displacive component similar to d0-ness as the origin of ferroelectricity.

Abstract

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.