7-11 July 2014
Africa/Johannesburg timezone
<a href="http://events.saip.org.za/internalPage.py?pageId=16&confId=34"><font color=#0000ff>SAIP2014 Proceedings published on 17 April 2015</font></a>

Synthesis and characterization of mixed-valence LuFe<sub>2</sub>O<sub>4-&delta;</sub>: Effect of stoichiometry &delta;

8 Jul 2014, 11:10
D Les 202

D Les 202

Oral Presentation Track A - Division for Physics of Condensed Matter and Materials DPCMM2


Mr Adli Peck (University of Johannesburg)

Abstract content <br> &nbsp; (Max 300 words)<br><a href="http://events.saip.org.za/getFile.py/access?resId=0&materialId=0&confId=34" target="_blank">Formatting &<br>Special chars</a>

LuFe2O4 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 Fe2+/Fe3+ ratio and magnetic ordering temperature TN 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 LuFe2O4-δ, from a comparison of stoichiometric and oxygen deficient samples. Such samples of LuFe2O4-δ of varying oxygen stoichiometry, δ, have been synthesised by solid state reaction as a polycrystalline powder. These have been characterised by x-ray diffraction, 57Fe Mössbauer-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 LuFe2O4-δ sample. Magnetisation measurements show that TN 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).

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Main supervisor (name and email)<br>and his / her institution

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

Primary author

Mr Adli Peck (University of Johannesburg)


Dr Christine Martin (ENSICAEN) Dr Emanuela Carleschi (UJ) Dr Gildas Diguet (UJ) Prof. Giovanni Hearne (UJ) Mr Wisdom Nkosilathi Sibanda (University of Johannesburg)

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