Investigations of Sr3Fe2-xMnxO7-delta the n=2 Ruddlesden-Popper phases with d(3)/d(4) interactions

We have prepared a series of Mn substituted strontium ferrates, Sr3Fe2-xMnx O7-delta where x=2/3, 1 and 4/3, and investigated their properties with X-r ay diffraction, X-ray absorption near edge spectroscopy (XANES), Mossbauer spectroscopy, variable-temperature resistivity and magnetic susceptibility. These compounds are metastable and have to be prepared at high temperature s, >1250 degreesC, with solid state techniques followed by quenching in air to room temperature. As a consequence the compounds are oxygen deficient a nd contain some Fe3+. They are insulators and exhibit spin-glass like behav ior at low temperatures due to frustrated magnetic interactions between the disordered array of transition metal ions on the B site. Mossbauer and XAN ES spectra show that the B cations are not fully oxidized and that the Fe4 in these compounds are charge-disproportionated into Fe3+ and Fe5+ at low temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.