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要旨:
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.
