Investigations of Sr3Fe2−xMnxO7−δ the n=2 Ruddlesden–Popper phases with d3/d4 interactions

Abstract

We have prepared a series of Mn substituted strontium ferrates, Sr3Fe2−xMnxO7−δ where x=2/3, 1 and 4/3, and investigated their properties with X-ray diffraction, X-ray absorption near edge spectroscopy (XANES), Mössbauer spectroscopy, variable-temperature resistivity and magnetic susceptibility. These compounds are metastable and have to be prepared at high temperatures, >1250°C, with solid state techniques followed by quenching in air to room temperature. As a consequence the compounds are oxygen deficient and contain some Fe3+. They are insulators and exhibit spin-glass like behavior at low temperatures due to frustrated magnetic interactions between the disordered array of transition metal ions on the B site. Mössbauer and XANES 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.