Origin of single-domain helicity/triangular-chirality selection in Ba3NbFe3Si2O14

Determine the microscopic mechanism that selects a single helicity and associated triangular chirality in Ba3NbFe3Si2O14, given that the zero-temperature mean-field Heisenberg model with interplane exchanges J3–J5 yields two energetically favorable (ε_H, ε_Hε_T) solutions; specifically, ascertain whether the Dzyaloshinskii–Moriya antisymmetric exchange lifts this degeneracy and accounts for the observed unique domain.

Background

The authors observe that in the structurally chiral langasite Ba3NbFe3Si2O14, neutron experiments reveal a single helicity together with a single triangular chirality, fixed by the structural chirality. Mean-field analysis with five exchange parameters (J1–J5) explains the helical modulation and favors two possible (ε_H, ε_Hε_T) solutions, but does not uniquely select one.

Polarized neutron results show that only one of these solutions is realized experimentally. The authors note that the origin of this final selection is not explained by their mean-field model and suggest that Dzyaloshinskii–Moriya antisymmetric exchange, which is symmetry-allowed in this compound and hinted at by a small ferromagnetic component along the c-axis, could be responsible.