Ferrotoroidicity in Cs₂FeCl₅·D₂O

The promise of antiferromagnetic spintronics largely relies on the possibilities of electrical manipulation of antiferromagnetic states, which requires the exploration of innovative material platforms to meet the challenge. Erythrosiderite-type compounds constitute a class of non-oxide materials presenting magneto-electric couplings ranging from multiferroicity to linear magneto-electric behaviour. In this communication, we demonstrate that Cs₂[FeCl₅(D₂O)] shows evidence of another ferroic order, ferrotoroidicity, providing an alternative way of manipulating the magnetic states. The magnetic structure of this compound (a collinear antiferromagnet with moments along b) allows a toroidal moment in the ac-plane. We have used spherical neutron polarimetry on a single crystal of Cs₂[FeCl₅(D₂O)] cooled in different configurations of applied electric (E) and magnetic (H) fields to show that the toroidal domains can be selected by a conjugate field (ExH) coupling with the c-component of the toroidal moment. The extraordinary sensitivity of spherical neutron polarimetry allows detecting and quantifying this toroidal domain selection.