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.

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.