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Abstract

Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder compounds AEFe(2)Ch(2)O (AE = Ba, Sr; Ch = S, Se). Powders and small single crystals of SrFe2S2O and SrFe2Se2O were synthesized from SrO, Fe, and Ch (S, Se). X-ray diffraction data were used to determine the crystal structures, which showed prominent magnetic ladderlike sublattices. The Mossbauer spectra of SrFe2S2O and SrFe2Se2O suggest the presence of localized divalent Fe ions in the FeCh(3)O structural units (distorted e(3)t(2)(3) configuration, S = 2). Single sharp hyperfine patterns at 5 K indicate the formation of simple antiferromagnetic ground states. The spin-ordering transitions (T-N) were determined by magnetic, resistivity, and specific heat data to be 216 and 228 K for SrFe2S2O and SrFe2Se2O, respectively. At ca. 540 K, both compounds exhibit a similar broad maximum in (T-max). In comparison with BaFe2S2O and BaFe2Se2O, the Sr homologues have higher T-max values, which suggest stronger intersite exchange interactions in accordance with the chemical pressure from the replacement of Sr atoms with Ba atoms. However, the lower Neel temperatures for the Sr homologues supports the idea that magnetic frustration is present, and it clearly has to be considered for this group of compounds.