Spin crossover in liquid (Mg,Fe)O at extreme conditions
Spin crossover in liquid (Mg,Fe)O at extreme conditions
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DOI：
10.1103/physrevb.93.195142
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发表时间：
2016-05-20
影响因子：
3.7
通讯作者：
Stixrude, L.
中科院分区：
文献类型：
--
作者：
Holmstrom, E.;Stixrude, L.
我们使用第一性原理的自由能计算预测的压力引起的自旋交叉在液体行星材料（Mg，Fe）O，从而Fe离子的磁矩逐渐消失在数百GPa的范围内。由于电子熵强烈地倾向于Fe的低自旋态，交叉具有负的有效克拉珀龙斜率，与这种过渡金属氧化物的晶体对应物形成鲜明对比。液态（Mg，Fe）O的扩散系数与MgO相似，对元素和自旋态的依赖性较弱。Fe-O和Mg-O配位随着压力从0到200 GPa从约4增加到7。我们发现分区的铁诱导晶体和熔体之间的密度反转，这意味着分离的基底岩浆海洋从surfaceone在早期地球。的自旋交叉诱导异常的密度对比度，和相反签署克拉珀龙斜率的交叉在液相和结晶相意味着，固-液转变诱导自旋转变（Mg，Fe）O。
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.