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

Abstract

MnSb2O6 is based on the structural chiral P321 space group No. 150 where the magnetic Mn2+ moments (S=5/2, L≈0) order antiferromagnetically at TN=12K. Unlike the related iron based langasite (Ba3NbFe3Si2O14) where the low-temperature magnetism is based on a proper helix characterized by a time-even pseudoscalar “magnetic” chirality, the Mn2+ ions in MnSb2O6 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 MnSb2O6 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 the application of a magnetic field ∥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 ≈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.