| Abstract
| - A polycrystalline sample of a new phase in the Sr−Fe−Mn−O system has been prepared by standard solid-statetechniques. Characterization at room temperature by X-ray diffraction, high-resolution electron microscopy,Mössbauer spectroscopy and neutron diffraction has led to it being described as a 15-layered, rhombohedral(15R) perovskite [space group R3̄m: a = 5.4489(1) Å, c = 33.8036(7) Å] with a previously unobserved structure.The pseudo close-packed SrO3 layers have a (cchch)3 stacking sequence such that the occupation of the interstitial6-coordinate sites by Mn (or Fe) leads to the formation of Mn2O9 units which are linked to each other eitherdirectly by a common vertex, or indirectly via a single, vertex-sharing MnO6 octahedron. The stoichiometry ofthe compound was determined to be SrMn0.915(5)Fe0.085(5)O2.979(3). The face-sharing sites are occupied by0.957(3)Mn/0.043(3)Fe while the exclusively corner-linked sites show a higher Fe occupation; 0.745(4)Mn/0.255(4)Fe. A neutron diffraction experiment carried out at 3 K indicated the presence of long-range magneticorder with the Mn4+ cations aligned antiferromagnetically with an ordered moment of 2.26(3)μB/Mn4+. Both theneutron and the susceptibility data are consistent with the Fe cations remaining magnetically disordered to 3 K.The latter data show TN = 220 K, and suggest that some spin frustration is present at low temperatures.
- A novel crystal structure is reported for SrMn0.915(5)Fe0.085(5)O2.979(3). Characterization by X-ray diffraction, high-resolution electron microscopy, Mössbauer spectroscopy, and neutron diffraction has led to this 15-layered perovskite described by the space group R3̄m, a = 5.4489(1) Å, c = 33.8036(7) Å. Below TN = 220 K the Mn4+ cations align antiferromagnetically, with an ordered moment of 2.26(3) μB/Mn4+ at 3 K. Magnetic susceptibility data, considered with the neutron diffraction data, are consistent with the Fe cations remaining magnetically disordered to 3 K.
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