In a recent paper, Vidya et al. investigated the structural, electronic, and magnetic properties of mixed-valence Sr4Fe4O11 by spin-polarized electronic-structure calculations. The crystal structure of this O-vacancy-ordered perovskite contains square pyramidal Fe(1)s and distorted octahedral Fe(2)o sites. Only one of the sub-lattices was magnetically ordered below TN~230K. Vidya et al. claimed that their calculations unambiguously show that the formal Fe3+ ions reside in the square pyramidal and the Fe4+ ions in the octahedral sites, in contrast to the previous assignment. In addition, Vidya et al. implied that rather the Fe4+ than the Fe3+ sub-lattice was magnetically ordered. It was pointed out that the structural and Mössbauer data clearly favor the assignment of Hodges et al. and were in disagreement with previous results. The Mössbauer spectra showed that it was the Fe3+ sub-lattice which was magnetically ordered.

Comment on “Spin- and Charge-Ordering in Oxygen-Vacancy-Ordered Mixed-Valence Sr4Fe4O11”. P.Adler: Physical Review B, 2008, 77[13], 136401 (3pp)