Neutron diffraction in MnSb2O6: Magnetic and structural domains in a helicoidal polar magnet with coupled chiralities

TL;DR

This study uses neutron diffraction to analyze the magnetic and structural domains in MnSb₂O₆, revealing how magnetic field influences its cycloidal structure and proposing a mechanism for its ferroelectric switching based on coupled chiralities.

Contribution

It provides new insights into the magnetic structure of MnSb₂O₆, showing the absence of a helicoidal phase and detailing how magnetic fields induce a cycloid-helix admixture, advancing understanding of magnetoelectric coupling.

Findings

No evidence for a helicoidal magnetic structure.

Magnetic field induces a cycloid-helix admixture.

Ferroelectric switching linked to structural and magnetic chiralities.

Abstract

MnSb$_{2}$O$_{6}$ is based on the structural chiral $P$321 space group #150 where the magnetic Mn$^{2+}$ moments ($S=5/2$, $L\approx 0$) order antiferromagnetically at $T_\mathrm{N}=12$ K. Unlike the related iron based langasite (Ba$_3$NbFe$_3$Si$_2$O$_{14}$) where the low temperature magnetism is based on a proper helix characterized by a time-even pseudoscalar `magnetic' chirality, the Mn$^{2+}$ ions in MnSb$_{2}$O$_{6}$ order with a cycloidal structure at low temperatures, described instead by a time-even vector `magnetic' polarity. A tilted cycloidal structure has been found [M. Kinoshita et al. Phys. Rev. Lett. 117, 047201 (2016)] to facilitate ferroelectric switching under an applied magnetic field. In this work, we apply polarized and unpolarized neutron diffraction analyzing the magnetic and nuclear structures in MnSb$_{2}$O$_{6}$ with the aim of understanding this magnetoelectric coupling. We find no evidence for a helicoidal magnetic structure with one of the spin envelope axes tilted away from the cycloidal $c$-axis. However, on application of a magnetic field $\parallel$ $\vec{c}$ the spin rotation plane can be tilted, giving rise to a cycloid-helix admixture that evolves towards a distorted helix (zero cycloidal component) for fields great than $\approx$ 2 T. We propose a mechanism for the previously reported ferroelectric switching based on coupled structural and magnetic chiralities requiring only an imbalance of structural chiral domains.