The magnetic ordering of ${\mathrm{La}}_{1/3}{\mathrm{Sr}}_{2/3}{\mathrm{FeO}}_3$ perovskite has been studied by neutron powder diffraction and ${}^{57}\mathrm{Fe}$ 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 $\mathbf{k}=(0,0,1)$ in $R\overline{3}c$ 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 a single Fe site, with a magnetic moment of 3.46(2)${\mu }_{\mathrm{B}}$ at 2 K. In the latter model, the magnetic moments of iron ions adopt the magnetic space group $C2/c$ or $C{2}^{\prime }/c^{\prime }$ and are aligned collinearly. The model allows the presence of two inequivalent Fe sites with magnetic moments of amplitude 3.26(3)${\mu }_{\mathrm{B}}$ and 3.67(2)${\mu }_{\mathrm{B}}$, respectively. The neutron-diffraction pattern is equally well fitted by either model. The Mössbauer spectroscopy study suggests a single charge state ${\mathrm{Fe}}^{3.66+}$ above the magnetic transition and a charge disproportionation into ${\mathrm{Fe}}^{(3.66-\zeta )+}$ and ${\mathrm{Fe}}^{(3.66+2\zeta )+}$ below the magnetic transition. The compatibility of the magnetic structure models with the Mössbauer spectroscopy results is discussed.

• Received 23 February 2018
• Revised 30 April 2018

DOI:https://doi.org/10.1103/PhysRevB.97.174417