Structure and magnetic properties of Sr 2FeO 4 and Sr 3Fe 2O 7 studied by powder neutron diffraction and Mössbauer spectroscopy

Sr 2FeO 4 and Sr 3Fe 2O 7 have been studied using low-temperature powder neutron diffraction, magnetometry and 57Fe Mössbauer spectroscopy. Sr 2FeO 4 orders antiferromagnetically at 60 K whilst the Néel temperature of Sr 3Fe 2O 7 is 110 K. At room temperature the Mössbauer spectrum of Sr 3Fe 2O 7 is interpreted in terms of a disproportionation, Fe 4+↔Fe 3+ + Fe 5+, though neutron diffraction measurements show a single, crystallographic iron site. Neutron diffraction data collected below the Néel temperatures from Sr 2FeO 4 (4 K) and Sr 3Fe 2O 7 (6 and 90 K) only show broad weak magnetic reflections indicative of antiferromagnetic ordering in two dimensions. Mossbauer data collected below T N from Sr 2FeO 4 indicate the presence of at least four magnetically different Fe 4+ sites.