ABSTRACT Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder ... more ABSTRACT Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder compounds AEFe2Ch2O (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 Mössbauer spectra of SrFe2S2O and SrFe2Se2O suggest the presence of localized divalent Fe ions in the FeCh3O structural units (distorted e3t23 configuration, S = 2). Single sharp hyperfine patterns at 5 K indicate the formation of simple antiferromagnetic ground states. The spin-ordering transitions (TN) 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 χ (Tχmax). In comparison with BaFe2S2O and BaFe2Se2O, the Sr homologues have higher Tχmax 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 Néel 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.
ABSTRACT The title compound is prepared by solid state reaction of BaO, Fe, and S (quartz tube, 8... more ABSTRACT The title compound is prepared by solid state reaction of BaO, Fe, and S (quartz tube, 800 °C, 100 h) and characterized by single crystal XRD, magnetic measurements, and Moessbauer spectroscopy.
CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+ ions in tetrahedral ... more CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+ ions in tetrahedral coordination. Here we characterize its magnetic properties by magnetization measurements and investigate its local electronic structure using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination with multiplet cluster and spin-resolved band structure calculations. We found that the Fe2+ ion in the unusual
Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) ... more Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) through green tea (GT) polyphenols produced water-soluble Fe3O4 nanocrystals coated with GT extracts namely epigallocatechin gallate (EGCG) and epicatechin (EC). Electron donating polyphenols stoichiometrically reduced Fe(3+) ions into Fe(2+) ions resulting in the formation of magnetite (Fe3O4) nanoparticles and corresponding oxidized products (semiquinones and quinones) that simultaneously served as efficient surface chelators for the Fe3O4 nanoparticles making them dispersible and stable in water, PBS, and cell culture medium for extended time periods. As-formed iron oxide nanoparticles (2.5-6 nm) displayed high crystallinity and saturation magnetization as well as high relaxivity ratios manifested in strong contrast enhancement observed in T2-weighted images. Potential of green tea-coated superparamagnetic iron oxide nanocrystals (SPIONs) as superior negative contrast agents was confirmed by in vitro and in vivo experiments. Primary human macrophages (J774A.1) and colon cancer cells (CT26) were chosen to assess cytotoxicity and cellular uptake of GT-, EGCGq-, and ECq-coated Fe3O4 nanoparticles, which showed high uptake efficiencies by J774A.1 and CT26 cells without any additional transfection agent. Furthermore, the in vivo accumulation characteristics of GT-coated Fe3O4 nanoparticles were similar to those observed in clinical studies of SPIONs with comparable accumulation in epidermoid cancer-xenograft bearing mice. Given their promising transport and uptake characteristics and new surface chemistry, GT-SPIONs conjugates can be applied for multimodal imaging and therapeutic applications by anchoring further functionalities.
ABSTRACT Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder ... more ABSTRACT Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder compounds AEFe2Ch2O (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 Mössbauer spectra of SrFe2S2O and SrFe2Se2O suggest the presence of localized divalent Fe ions in the FeCh3O structural units (distorted e3t23 configuration, S = 2). Single sharp hyperfine patterns at 5 K indicate the formation of simple antiferromagnetic ground states. The spin-ordering transitions (TN) 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 χ (Tχmax). In comparison with BaFe2S2O and BaFe2Se2O, the Sr homologues have higher Tχmax 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 Néel 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.
ABSTRACT The title compound is prepared by solid state reaction of BaO, Fe, and S (quartz tube, 8... more ABSTRACT The title compound is prepared by solid state reaction of BaO, Fe, and S (quartz tube, 800 °C, 100 h) and characterized by single crystal XRD, magnetic measurements, and Moessbauer spectroscopy.
CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+ ions in tetrahedral ... more CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+ ions in tetrahedral coordination. Here we characterize its magnetic properties by magnetization measurements and investigate its local electronic structure using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination with multiplet cluster and spin-resolved band structure calculations. We found that the Fe2+ ion in the unusual
Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) ... more Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) through green tea (GT) polyphenols produced water-soluble Fe3O4 nanocrystals coated with GT extracts namely epigallocatechin gallate (EGCG) and epicatechin (EC). Electron donating polyphenols stoichiometrically reduced Fe(3+) ions into Fe(2+) ions resulting in the formation of magnetite (Fe3O4) nanoparticles and corresponding oxidized products (semiquinones and quinones) that simultaneously served as efficient surface chelators for the Fe3O4 nanoparticles making them dispersible and stable in water, PBS, and cell culture medium for extended time periods. As-formed iron oxide nanoparticles (2.5-6 nm) displayed high crystallinity and saturation magnetization as well as high relaxivity ratios manifested in strong contrast enhancement observed in T2-weighted images. Potential of green tea-coated superparamagnetic iron oxide nanocrystals (SPIONs) as superior negative contrast agents was confirmed by in vitro and in vivo experiments. Primary human macrophages (J774A.1) and colon cancer cells (CT26) were chosen to assess cytotoxicity and cellular uptake of GT-, EGCGq-, and ECq-coated Fe3O4 nanoparticles, which showed high uptake efficiencies by J774A.1 and CT26 cells without any additional transfection agent. Furthermore, the in vivo accumulation characteristics of GT-coated Fe3O4 nanoparticles were similar to those observed in clinical studies of SPIONs with comparable accumulation in epidermoid cancer-xenograft bearing mice. Given their promising transport and uptake characteristics and new surface chemistry, GT-SPIONs conjugates can be applied for multimodal imaging and therapeutic applications by anchoring further functionalities.
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Papers by Martin Valldor