Ba4KFe3O9: a novel ferrite containing discrete 6-membered rings of corner-sharing FeO4 tetrahedra.

ABSTRACT: Single crystals of a new iron-containing oxide, Ba(4)KFe(3)O(9), were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO(4) tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe(3+) coordination environments. The observed magnetic moment (~3.9 ?(B)) at 400 K is significantly lower than the calculated spin-only (~5.2 ?(B)) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe(3+) sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ~200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba(4)KFe(3)O(9) calculated from ?T data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ~ 2.01 that is characteristic of Fe(3+) ions in a tetrahedral environment, thus confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe(6) magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (?B(pp)). The line-width ratio ?B(pp)(major)/?B(pp)(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, ?(minor)/?(major) ~ 4.

SUBMITTER: Zhao Q 

PROVIDER: S-EPMC3214634 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature