Revisiting the Magnetic Structure and Charge Ordering in La$_{1/3}$Sr$_{2/3}$FeO$_3$ by Neutron Powder Diffraction and Mössbauer Spectroscopy

Abstract

The magnetic ordering of La 1/3 Sr 2/3 FeO 3 perovskite has been studied by neutron powder diffraction and 57 Fe Mössbauer spectroscopy down to 2 K. From symmetry analysis, a chiral helical model and a collinear model are proposed to describe the magnetic structure. Both are commensurate, with propagation vector k = (0,0,1) in R3c space group. In the former model, the magnetic moments of Fe adopt the magnetic space group P 3 2 21 and have helical and antiferromagnetic ordering propagating along the c axis. The model allows only single Fe site, with a magnetic moment of 3.46(2) µ B at 2 K. In the latter model, the magnetic moments of iron ions adopt the magnetic space group C2/c or C2 ′ /c ′ and are aligned collinearly. The model allows the presence of two inequivalent Fe sites with magnetic moments of amplitude 3.26(3) µ B and 3.67(2) µ B , respectively.The neutron diffraction pattern is equally well fitted by either model. The Mössbauer spectroscopy study suggests a single charge state Fe 3.66+ above the magnetic transition and a charge disproportionation into Fe (3.66−ζ)+ and Fe (3.66+2ζ)+ below the magnetic transition. The compatibility of the magnetic structure models with the Mössbauer spectroscopy results is discussed.