7-11 July 2014
Africa/Johannesburg timezone
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Synthesis and characterization of mixed-valence LuFe2O4-δ: Effect of stoichiometry δ

Presented by Mr. Adli PECK on 8 Jul 2014 from 11:10 to 11:30
Type: Oral Presentation
Session: DPCMM2
Track: Track A - Division for Physics of Condensed Matter and Materials


LuFe<sub>2</sub>O<sub>4</sub> exhibits a unique mixed-valence superstructure arising from charge-ordering (CO) within the lattice. The unit cell consists of a characteristic stacking of bi-layers, in which Fe is configured in a triangular network. This results in charge and spin frustration in the material, with a resulting plenitude of degenerate magnetic-electronic ground states. Furthermore the Fe is coordinated with oxygen in a trigonal bi-pyramidal polyhedron, a rather unusual co-ordination geometry for inorganic compounds. This mixed-valence characteristic within the bi-layers has been claimed to give rise to a dipole moment, i.e., ferroelectric effects arising from the CO. However such claims of electronically driven CO are under dispute [1]. Recent work has also demonstrated remarkable oxygen storage capacities in this compound [2]. Previous studies have indeed shown that the Fe<sup>2+</sup>/Fe<sup>3+</sup> ratio and magnetic ordering temperature T<sub>N</sub> are influenced by the oxygen stoichiometry [3-4]. We will report our investigations of the effect of oxygen stoichiometry on the CO and magnetic-electronic properties of LuFe<sub>2</sub>O<sub>4-&delta;</sub>, from a comparison of stoichiometric and oxygen deficient samples. Such samples of LuFe<sub>2</sub>O<sub>4-&delta;</sub> of varying oxygen stoichiometry, &delta;, have been synthesised by solid state reaction as a polycrystalline powder. These have been characterised by x-ray diffraction, <sup>57</sup>Fe M&ouml;ssbauer-effect spectroscopy (MES), SQUID magnetometry and TGA chemical analysis. Using different masses for the overall starting mixture has a radical effect on the purity of the as-synthesised LuFe<sub>2</sub>O<sub>4-&delta;</sub> sample. Magnetisation measurements show that T<sub>N</sub> is confined to 245-250 K for the synthesised samples, albeit with quite significant differences in the magnetisation-temperature envelopes. Variable cryogenic temperature MES measurements are used to compare the effect of oxygen content on both the CO and magnetic hyperfine structure. [1]. Angst M, Phys. Status Solidi RRL 7, 375 (2013). [2]. Hervieu M et al., Nature Materials 13, 74 (2013). [3]. Yang HX et al., J. Phys. Condens. Matter 24, 435901 (2012). [4]. Wang F et al., J. Appl. Phys. 113, 06 (2013).






Prof. Giovanni Hearne (ghearne@uj.ac.za) UJ Dept. Physics




Room: D Les 202

Primary authors