Comment on “Spin- and charge-ordering in oxygen-vacancy-ordered mixed-valence ${\mathrm{Sr}}_4{\mathrm{Fe}}_4{\mathrm{O}}_{11}$”

In a recent paper, Vidya et al. [Phys. Rev. B 74, 054422 (2006)] investigated the structural, electronic, and magnetic properties of mixed-valence ${\mathrm{Sr}}_4{\mathrm{Fe}}_4{\mathrm{O}}_{11}$ by spin-polarized electronic-structure calculations. The crystal structure of this oxygen-vacancy-ordered perovskite contains square pyramidal $\mathrm{Fe}{\left(1\right)}^s$ and distorted octahedral $\mathrm{Fe}{\left(2\right)}^o$ sites. Only one of the sublattices is magnetically ordered below $T_N\sim 230\mathrm{K}$. Vidya et al. claimed that their calculations unambiguously show that the formal ${\mathrm{Fe}}^{3+}$ ions reside in the square pyramidal and the ${\mathrm{Fe}}^{4+}$ ions in the octahedral sites, in contrast to the previous assignment by Hodges et al. [J. Solid State Chem. 151, 190 (2000)]. In addition, Vidya et al. implied that rather the ${\mathrm{Fe}}^{4+}$ than the ${\mathrm{Fe}}^{3+}$ sublattice is magnetically ordered. In this Comment, it is pointed out that the structural and Mössbauer data clearly favor the assignment of Hodges et al. and are in disagreement with the results of Vidya et al. The Mössbauer spectra evidence that it is the ${\mathrm{Fe}}^{3+}$ sublattice which is magnetically ordered.