Multipole orders and Bragg diffraction patterns for the chain ferrate Na_2FeSe-2

摘要

Fundamental block and staggered orders of magnetic Fe multipoles in Na_2FeSe-2 are classified by their symmetry and magneloelectric properties. Our minimal structure models incorporate ferromagnetic or antiferromagnetic coupling between chains, and they are not compatible with axial ferromagnetism. The ferrate salt is valued in studies of highly correlated electrons as the only iron selenide known to possess chainlike structural units hosting ferrous cations. Axial and polar (Dirac) multipoles are compulsory in the electronic structure since Fe ions exhibit enantiomorphic symmetry in the parent K_2ZnO_2-type compound. Calculated Bragg diffraction patterns for neutrons and x rays prove that the techniques can unlock individual contributions from both multipole types.