Magnetic Structures of Iron-based Materials: Through Complex Magnetism of CaFe₄As₃

Abstract

Magnetism of interpenetrating FeAs strips in the orthorhombic CaFe₄As₃ was examined through neutron diffraction. Incommensurate and predominantly longitudinally (||b) modulated order develops through a 2nd order phase transition at T_N ～ 90K. A 1st order transition at T₂ ～ 26K is associated with the development of components in a separate irreducible representation, locking the wave vector to 3b^*/8. The ab-initio Fermi surface features sheets separated by near the observed wave vector. However, Fermi surface nesting seems to have a limited role, instead magnetic structures could result from competing 2nd and 3rd nearest neighbor interactions in a localized spin picture.