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.