Single domain magnetic helicity and triangular chirality in structurally enantiopure Ba3NbFe3Si2O14.

A novel doubly chiral magnetic order is found in the structurally chiral langasite compound Ba3NbFe3Si2O14. The magnetic moments are distributed over planar frustrated triangular lattices of triangle units. On each of these they form the same triangular configuration. This ferrochiral arrangement is helically modulated from plane to plane. Unpolarized neutron scattering on a single crystal associated with spherical neutron polarimetry proved that a single triangular chirality together with a single helicity is stabilized in an enantiopure crystal. A mean-field analysis allows us to discern the relevance on this selection of a twist in the plane to plane super-superexchange paths.