Peets, D.C.; Kim, J.-H.; Dosanjh, P.; Reehuis, M.; Maljuk, A.; Aliouane, N.; Ulrich, C.; Keimer, B.: Magnetic phase diagram of Sr3Fe2O7-δ. Physical Review B 87 (2013), p. 214410/1-8
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Magnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe4+-containing perovskite-related phase Sr3Fe2O7-x as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully oxygenated compound (x = 0) exhibits a charge-disproportionation transition at TD = 340 K, and an antiferromagnetic transition at TN = 115 K. For temperatures T < TD, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe4+ moments. The fully deoxygenated compound (x = 1) is highly insulating, and its Fe3+ moments exhibit commensurate antiferromagnetic order below TN similar to 600 K. Compounds with intermediate delta exhibit different order with lower TN, likely as a consequence of frustrated exchange interactions between Fe3+ and Fe4+ sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported.