STRUCTURE AND MAGNETIC-PROPERTIES OF SR2FEO4 AND SR3FE2O7 STUDIED BY POWDER NEUTRON-DIFFRACTION AND MOSSBAUER-SPECTROSCOPY

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