Charge and magnetic ordering dynamics under pressure in LuFe2O4
Presented by Mr. Wisdom Nkosilathi SIBANDA on 9 Jul 2014 from 17:10 to 19:00
Type: Poster Presentation
Track: Track A - Division for Physics of Condensed Matter and Materials
Board #: A.216
Multiferroics offer the possibility to combine ferroelectric and magnetic ordering in materials, hence the realisation of multifunctional devices . LuFe<sub>2</sub>O<sub>4</sub> is one such compound. Initially thought to be the prototypical compound for charge-order (CO) based ferroelectricity, nowadays it is attracting interest because of its pronounced magneto-electronic coupling, as well as the spin/charge frustration anticipated in the triangular network of Fe atoms within the bilayers of the rhombohedral unit cell. Previous work has shown that the low pressure (LP) phase has a T<sub>N</sub> ≈ 250 K and a CO temperature of 330 K in the highly stoichiometric sample investigated here . In this work pressure has been used as a thermodynamic variable to tune the magnetic-electronic properties of LuFe<sub>2</sub>O<sub>4</sub>. Generation of hydrostatic pressure was by means of a diamond anvil cell, and <sup>57</sup>Fe Mössbauer spectroscopy (MS) was used to probe magnetic-electronic phase transformations. Measurements were performed up to ~30 GPa at room temperature. We find evidence of an electron hopping component Fe<sup>2+</sup><->Fe<sup>3+</sup> already present at ambient pressure on the time scale of the Mössbauer effect, with a hopping frequency of 1.4 MHz. At ~5 GPa the CO breaks down, and the hopping component completely dominates, with the hopping frequency increasing to ~10 MHz. The MS spectral line shape at 7 GPa shows new emerging features, supposed to be evidence of a new structural phase initiating at this pressure, consistently with previous x-ray diffraction studies . Furthermore, at 10 GPa new magnetic hyperfine structure is observed in the high pressure (HP) phase at room temperature. This suggests a change of the LP spin frustrated state to that of a new magnetic-state in the HP phase ‘with reduced frustration’. The MS spectral envelope of the HP phase suggests that two magnetic-electronic states co-exist, a new CO state is stabilised at HP and unusual spin states are also involved. This is consistent with the claims of previous x-ray and electron diffraction studies of this HP phase recovered to ambient conditions .  X. S. Xu et al., PRL 101, 227602 (2008).  S. Lafuerza et al., PRB 88, 201304 (2013).  A. D. Christianson et al., PRL 100, 107601 (2008).  J. Rouquette et al., PRL 105, 237203 (2010).
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