# Ferroelectricity induced by ferriaxial crystal rotation and spin helicity in a B-site-ordered double-perovskite multiferroic In2NiMnO6

## TL;DR

This study reveals that In2NiMnO6 exhibits ferroelectricity below 26 K due to complex magnetic structures and spin-helicity coupling with crystal rotation, expanding understanding of multiferroic mechanisms in B-site-ordered double perovskites.

## Contribution

It demonstrates ferroelectricity induced by ferriaxial crystal rotation and spin helicity in In2NiMnO6, highlighting a novel coupling mechanism in B-site-ordered double perovskites.

## Key findings

- Ferroelectric polarization observed below 26 K.
- Complex noncollinear magnetic structure with cycloidal and screw components.
- Coupling between spin helicity and crystal rotation explains polarization.

## Abstract

We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P ~ 30 {\mu}C/m2, is observed in a polycrystalline sample below TN = 26 K where a magnetic phase ransition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with "cycloidal" and "proper screw" components appears below TN, which has the incommensurate propagation vector k = (ka,0,ks; ka ~ 0.274, ks ~ -0.0893). The established magnetic point group 21' implies that the macroscopic ferroelectric polarization is along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii-Moriya effect allow us to specify two distinct contributions to the polarization of In2NiMnO6. One of them is associated with the cycloidal component, p1 ~ rij x (Si x Sj), and the other with the proper screw component, p2 ~ [rij (Si x Sj )]A. The latter is explained by coupling between spin helicity and "ferriaxial" crystal rotation with macroscopic ferroaxial vector A, characteristic of the B-site ordered perovskite systems with out-of-plane octahedral tilting.

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Source: https://tomesphere.com/paper/1903.00363