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

Research output: Contribution to journalArticleScientificpeer-review

Researchers

  • Eero Holmström
  • L. Stixrude

Research units

  • University College London

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.

Details

Original languageEnglish
Article number195142
Number of pages7
JournalPhysical Review B
Volume93
Issue number19
Publication statusPublished - 20 May 2016
MoE publication typeA1 Journal article-refereed

    Research areas

  • 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

ID: 4684249