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.
Categories: cond-mat.str-el cond-mat.mtrl-sci