Phonon dispersions throughout the iron spin crossover in ferropericlase

Influence of the iron spin crossover in ferropericlase on the lower mantle geotherm

The iron spin crossover in ferropericlase introduces anomalies in its thermodynamics and thermoelastic properties. Here we investigate how these anomalies can affect the lower mantle geotherm. The effect is examined in mantle aggregates consisting of mixtures of bridgmanite, ferropericlase, and CaSiO$_3$ perovskite, with different Mg/Si ratios varying from harzburgitic to perovskitic (Mg/Si$\sim$1.5 to 0.8). We find that the anomalies introduced by the spin crossover increase the isentropic gradient and thus the geotherm proportionally to the amount of ferropericlase. The geotherms can be as m…

铁 spin crossover 在 ferropericlase 中及其对下地 mantle 热导率的影响

Iron spin crossover in ferropericlase and its effect on lower-mantle thermal conductivity

通过直接测量单晶 ferropericlase 的热导率，发现铁 spin crossover 导致热导率在 60-100 GPa 和 1700 K 时显著降低，影响下地 mantle 热导率分布。

Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

We present LDA+$U_{sc}$ calculations of high-spin (HS) and low-spin (LS) states in ferropericlase (fp) with an iron concentration of 18.75$\%$. The Hubbard parameter $U$ is determined self-consistently with structures optimized at arbitrary pressures. We confirm a strong dependence of $U$ on the pressure and spin state. Static calculations confirm that the antiferromagnetic configuration is more stable than the ferromagnetic one in the HS state, consistent with low-temperature measurements. Phonon calculations guarantee the dynamical stability of HS and LS states throughout the pressure range …

Intermediate spin state and the B1-B2 transition in ferropericlase at tera-Pascal pressures

Ferropericlase (fp), (Mg$_{1-x}$Fe$_x$)O, the second most abundant mineral in the Earth's lower mantle, is expected to be an essential component of super-Earths' mantles. Here we present an ab initio investigation of the structure and magnetic ground state of fp up to $\sim$ 3 TPa with iron concentrations (x$_{Fe}$) varying from 0.03 to 0.12. Calculations were performed using LDA+U$_{sc}$ and PBE exchange-correlation functionals to elucidate the pressure range for which the Hubbard U (U$_{sc}$) is required. Similar to the end-members FeO and MgO, fp also undergoes a B1 to B2 phase transition t…

Bullen's parameter as a seismic observable for spin crossovers in the lower mantle

Elastic anomalies produced by the spin crossover in ferropericlase have been documented by both first principles calculations and high pressure-temperature experiments. The predicted signature of this spin crossover in the lower mantle is, however, subtle and difficult to geophysically observe within the mantle. Indeed, global seismic anomalies associated with spin transitions have not yet been recognized in seismologic studies of the deep mantle. A sensitive seismic parameter is needed to determine the presence and amplitude of such a spin crossover signature. The effects of spin crossovers o…

下地幔铁方镁石的量子临界点和自旋涨落

Quantum critical point and spin fluctuations in the lower-mantle ferropericlase

铁长石（Mg，Fe）O是地球下地幔中含量最丰富的矿物之一。Fe 2+离子的高自旋（HS）到低自旋（LS）跃迁可以显著改变地幔深部（Mg，Fe）O的物理和化学性质，从而改变我们对地球深部内部的认识。为了对铁的基态电子态有一个基本的了解，在高压和低温（低至5 K）下，用透射（TMS）和同步加速器（NFS）穆斯堡尔谱研究了（Mg 0. 75，Fe 0. 25）O中Fe 2+的电子态和磁态.结果表明，Fe ~（2+）在自旋跃迁的临界压力Pc和T=0附近的基态电子态是由一个量子临界点Pq（T = 0，Pc）决定的，在这个量子临界点上，HS态和LS态的能量差（自旋涨落的能隙）为零.偏离T=0导致HS或LS态的热激发，这表明对材料的磁性和物理性质有很强的影响。结合理论计算，结果表明，零温量子临界点的存在不仅影响低温物理性质，而且在与下地幔中层有关的条件下，影响强温压相关性质.