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 ne utron diffraction, magnetometry and Fe-57 Mossbauer spectroscopy. Sr2F eO4 orders antiferromagnetically at 60 K whilst the Neel temperature o f Sr3Fe2O7 is 110 K. At room temperature the Mossbauer spectrum of Sr3 Fe2O7 is interpreted in terms of a disproportionation, Fe 4+ <-- -->Fe 3+ + Fe5+, though neutron diffraction measurements show a single, crys tallographic iron site. Neutron diffraction data collected below the N eel temperatures from Sr2FeO4 (4 K) and Sr3Fe2O7 (6 and 90 K) only sho w broad weak magnetic reflections indicative of antiferromagnetic orde ring in two dimensions. Mossbauer data collected below TN from Sr2FeO4 indicate the presence of at least four magnetically different Fe4+ si tes.