Atomic and magnetic structures, disorder effects, and unconventional superexchange interactions in (formula presented) oxides of layered brownmillerite-type structure

V. Yu Pomjakushin, A. M. Balagurov, T. V. Elzhov, D. V. Sheptyakov, P. Fischer, D. I. Khomskii, V. Yu Yushankhai, A. M. Abakumov, M. G. Rozova, E. V. Antipov, M. V. Lobanov, S. J.L. Billinge

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3 Citations (Scopus)

Abstract

Crystal and magnetic structures of complex manganese oxides (formula presented) were studied by neutron powder diffraction (ND) and (formula presented) technique in the temperature range 2-300 K. The crystal structures contain single (formula presented) layers separated by three nonmagnetic cation-oxygen layers. The principal difference between the (formula presented) compounds is the Mn valence: (formula presented) or (formula presented) and the structure of the (formula presented) buffer layer, which is formed by tetrahedra or partially filled octahedra, respectively. The magnetic moments of the manganese ions are coupled antiferromagnetically in the (formula presented) plane, but antiferromagnetically (formula presented) type) or ferromagnetically (formula presented) type) between the planes for the reduced and oxidized compositions, respectively. The transition from the G- to C-type magnetic structure by oxygen doping is explained by strong diagonal (formula presented) superexchange antiferromagnetic interaction between (formula presented)-ions in the adjacent layers through additional oxygen atoms in the GaO buffer layer. The magnetic moments in Sr-based samples are appreciably reduced in comparison with the spin-only values of the corresponding Mn ion. By using complementary information on local magnetic field distribution from (formula presented) we show that the reduced magnetic moments seen by ND are caused by the presence of locally flipped Mn spins and a short-ranged (formula presented) antiferromagnetic phase. The magnetic disorder can be caused by the disorder observed in the oxygen positions of the (formula presented) layer, because the coupling between the (formula presented) layers is mediated by the geometry of the superexchange path through these oxygen atoms.

Original languageEnglish
Pages (from-to)1-13
Number of pages13
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume66
Issue number18
DOIs
Publication statusPublished - 2002
Externally publishedYes

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