Structure and magnetic properties of Sr2FeO4 and Sr3Fe2O7 studied by powder neutron diffraction and Mössbauer spectroscopy

Abstract

Sr₂FeO₄ and Sr₃Fe₂O₇ have been studied using low-temperature powder neutron diffraction, magnetometry and ⁵⁷Fe Mössbauer spectroscopy. Sr₂FeO₄ orders antiferromagnetically at 60 K whilst the Néel temperature of Sr₃Fe₂O₇ is 110 K. At room temperature the Mössbauer spectrum of Sr₃Fe₂O₇ is interpreted in terms of a disproportionation, Fe⁴⁺↔ Fe³⁺+ Fe⁵⁺, though neutron diffraction measurements show a single, crystallographic iron site. Neutron diffraction data collected below the Néel temperatures from Sr₂FeO₄(4 K) and Sr₃Fe₂O₇(6 and 90 K) only show broad weak magnetic reflections indicative of antiferromagnetic ordering in two dimensions. Mössbauer data collected below T_N from Sr₂FeO₄ indicate the presence of at least four magnetically different Fe⁴⁺ sites.