Displacive-type ferroelectricity from magnetic correlations within spin-chain

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 Néel temperature of (TN = ) 32 K. 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.

Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5

“…We wonder whether there is any additional factor playing a role, that is, the radial extension/contraction of 4f orbital, to create the local distortion of Ni-O responsible for the ferroelectricity in this series. 6 The different amount of distortion of NiO 6 octahedra in different rare-earth members 18 supports our conclusion on this aspect.…”

“…The reason is that similar inferences have made by us in some other families as well in recent years, [15][16][17] where the magnetoelectric coupling is strong. We have tried to look for ferroelectricity observed for heavy rare-earth members; 4,6,8 however, we could not detect the same (that is, remnant polarization and its reversibility of sign with opposite poling by electric field by measuring pyroelectric current) in this compound. We wonder whether there is any additional factor playing a role, that is, the radial extension/contraction of 4f orbital, to create the local distortion of Ni-O responsible for the ferroelectricity in this series.…”

Extraordinarily large intrinsic magnetodielectric coupling of the Tb member within the Haldane spin-chain family R2BaNiO5

“…25] 31]. In sharp contrast to this behavior of Tb compound, we find that the value does not even exceed a few percent for other R members, e.g., Nd, Gd, Dy and Er members [7,[19][20][21][22][23]. The fact that the Tb member alone stands out in this respect rules out any direct role of the Haldane spin-chain.…”

“…The space group Immm is centrosymmetric and hence unfavorable for ferroelectricity. However, a small displacement of the atoms around NiO6 octahedra, following exchange-striction, can result [7] in non-centrosymmetric space group, Imm2. We therefore searched for ferroelectricity.…”

Complex nature of magnetic field induced ferroelectricity in GdCrTiO5

“…2,3,4 Nevertheless, there are many systems (such as, Haldane spin-chain systems), where the cross-coupling mechanism is not well understood. 5,6,7 Even in well-known multiferroic compounds like RMn 2 O 5 (R = rare-earth), 8 crystallizing in an orthorhombic structure with Pbnm space group, the mechanism is still under debate. 9,10 Initially, there were contradictory reports on the mechanism of magnetoelectricity.…”