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Spin crossover in liquid (Mg,Fe)O at extreme conditions

Holmstrom, E; Stixrude, L; (2016) Spin crossover in liquid (Mg,Fe)O at extreme conditions. Physical Review B , 93 (19) , Article 195142. 10.1103/PhysRevB.93.195142. Green open access

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Abstract

We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O.

Type: Article
Title: Spin crossover in liquid (Mg,Fe)O at extreme conditions
Open access status: An open access version is available from UCL Discovery
DOI: 10.1103/PhysRevB.93.195142
Publisher version: https://doi.org/10.1103/PhysRevB.93.195142
Language: English
Additional information: © 2016 American Physical Society.
Keywords: Science & Technology, Physical Sciences, Physics, Condensed Matter, Physics, INITIO MOLECULAR-DYNAMICS, TOTAL-ENERGY CALCULATIONS, MOLTEN FEO-SIO2 SYSTEM, EARTHS LOWER MANTLE, WAVE BASIS-SET, HIGH-PRESSURE, PHASE-TRANSITIONS, 1ST PRINCIPLES, MGSIO3 LIQUID, SILICATE MELT
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1518001
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