Transport properties of iron at Earth's core conditions: The effect of spin disorder

Drchal, V.; Kudrnovský, J.; Wagenknecht, David; Turek, I.; Khmelevskyi, Sergii

doi:10.1103/physrevb.96.024432

Cited by 24 publications

(22 citation statements)

References 43 publications

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“…That analogy, however, has serious implications, as it is known that impurities in some cases cause inelastic electron scattering that preserves charge but not the energy (Giuliani & Vignale, ; Koshino, ; Taylor, ; Uher, ). In a liquid Fe alloy containing ISRO structures at the core conditions, inelastic scattering from ISROs could result from the presence of local magnetic moments and spin scattering within those structures, which is in line with the discussion by Drchal et al (). The ISRO structures in the melt, due to their densely packed order relative to the rest of the liquid, will affect the magnitude and the consideration of potential experienced by the electrons (e.g., Faber, ).…”

Section: Discussionsupporting

confidence: 86%

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

et al. 2019

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The electrical resistivity and thermal conductivity of liquid Fe alloys are the least constrained parameters in Earth's outer core (OC). These parameters are important as they modulate energy budget available for the geodynamo and affect the spatiotemporal evolution of the core. We report results of electrical resistivity measurements on solid and liquid Fe‐4.5 wt%Si from 3–9 GPa using a large volume multianvil press. The internally modified 18/11 octahedron cell was used to maintain the geometry of the liquid sample and to delay the onset of contamination. Electrical resistivity of solid Fe‐4.5Si decreases steadily with pressure and is very sensitive to increasing temperature‐driven onset of phase transitions. Along the melting boundary and within error, electrical resistivity remains constant and assumes the same value of 120 μΩcm as observed in pure liquid Fe. The results are interpreted in the context of icosahedral short‐range order (ISRO) structures that exhibit higher concentration with increasing pressure. Along the melting line, the increasing concentration of ISROs reduces charge carrier mean free path and prevents decrease of electrical resistivity with increasing pressure as seen in liquid metals, Cu, Ag, and Au, which do not have ISROs. In light of recent developments in understanding of the structure and dynamics of liquid transition metals and alloys, we postulate that our findings are applicable to other Fe alloys in the OC with small light element (C, S, and O) content. We calculated an adiabatic heat flow of 9.4–12 TW at the OC‐CMB interface, which admits thermal convection.

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Section: Discussionsupporting

confidence: 86%

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

et al. 2019

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“…Figure 6 also implies the violation of the Matthiessen's rule, which is a simple sum rule of resistivity of all the scattering terms. The violation of the Matthiessen's rule is already reported by previous calculations (Glasbrenner et al, 2014;Gomi et al, 2016;Drchal et al, 2017).…”

Section: Concentrated Alloyssupporting

confidence: 70%

“…Although the solid phase crystal structure is important, we simply assumed that the hcp Fe alloys are good proxy. The spin disorder scattering is potentially important (Drchal et al, 2017), especially for small planets with hydrogen containing core (Gomi et al, 2018). But in this study, we neglect this effect.…”

Section: Electrical Resistivity and Thermal Conductivity Of The Earthmentioning

confidence: 99%

Impurity Resistivity of fcc and hcp Fe-Based Alloys: Thermal Stratification at the Top of the Core of Super-Earths

Gomi

Yoshino

2018

Front. Earth Sci.

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It is widely known that the Earth's Fe dominant core contains a certain amount of light elements such as H, C, N, O, Si, and S. We report the results of first-principles calculations on the band structure and the impurity resistivity of substitutionally disordered hcp and fcc Fe based alloys. The calculation was conducted by using the AkaiKKR (machikaneyama) package, which employed the Korringa-Kohn-Rostoker (KKR) method with the atomic sphere approximation (ASA). The local density approximation (LDA) was adopted for the exchange-correlation potential. The coherent potential approximation (CPA) was used to treat substitutional disorder effect. The impurity resistivity is calculated from the Kubo-Greenwood formula with the vertex correction. In dilute alloys with 1 at. % impurity concentration, calculated impurity resistivities of C, N, O, S are comparable to that of Si. On the other hand, in concentrated alloys up to 30 at. %, Si impurity resistivity is the highest followed by C impurity resistivity. Ni impurity resistivity is the smallest. N, O, and S impurity resistivities lie between Si and Ni. Impurity resistivities of hcp-based alloys show systematically higher values than fcc alloys. We also calculated the electronic specific heat from the density of states (DOS). For pure Fe, the results show the deviation from the Sommerfeld value at high temperature, which is consistent with previous calculation. However, the degree of deviation becomes smaller with increasing impurity concentration. The violation of the Sommerfeld expansion is one of the possible sources of the violation of the Wiedemann-Franz law, but the present results could not resolve the inconsistency between recent electrical resistivity and thermal conductivity measurements. Based on the present thermal conductivity model, we calculated the conductive heat flux at the top of terrestrial cores, which is comparable to the heat flux across the thermal boundary layer at the bottom of the mantle. This indicates that the thermal stratification may develop at the top of the liquid core of super-Earths, and hence, chemical buoyancies associated with the inner core growth and/or precipitations are required to generate the global magnetic field through the geodynamo.

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“…New diamond anvil cell (DAC) experimental data 6 , 13 – 15 place constraints on the k of lower mantle minerals, which subsequently limits the magnitude of heat flux through the CMB. These experimental results are complemented by numerical studies 16 , 17 of Fe at core conditions which demonstrate the important role of electron-electron scattering and spin disorder. The absence of a consensus on k and uncertainty in ohmic losses in the core necessitate a consideration of alternative sources of energy required to generate the Earth’s magnetic field throughout history 18 .…”

Section: Introductionmentioning

confidence: 88%

Electrical resistivity of liquid Fe to 12 GPa: Implications for heat flow in cores of terrestrial bodies

Silber

Secco

Littleton

2018

Sci Rep

124

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Electrical and thermal transport properties of liquid Fe under high pressure have important implications for the dynamics and thermal evolution of planetary cores and the geodynamo. However, electrical resistivity (ρ) and thermal conductivity (k) of liquid Fe at high pressure still remain contentious properties. To date, only two experimental investigations of ρ of liquid Fe in the pressure region below 7 GPa are reported in literature. Here we report the results of measurements of ρ for solid and liquid Fe (inversely proportional to k through the Wiedemann-Franz law) at pressures from 3 to 12 GPa, using a large multi-anvil press. We show that ρ of liquid Fe decreases as a function of pressure up to the δ-γ-liquid triple point at ~5.2 GPa, and subsequently remains invariant from 6 to 12 GPa, which is consistent with an earlier study on liquid Ni. Our results demonstrate an important effect of solid phase on the structure and properties of liquid Fe. Our values of ρ for solid and liquid Fe are used to calculate k in Mercury’s solid inner core and along the adiabat in the liquid outer cores of Moon, Ganymede, Mercury and Mars. Our robust values of thermal conductivity place the focus on uncertainties in thermal expansion as the cause of variation in values of core conducted heat. Except for Mercury, our adiabatic heat flux values in these terrestrial cores validate the use of similar values used in several previous studies. Our high values of core adiabatic heat flux in Mercury would provide a stabilizing effect on, and lead to an increase in thickness of, the thermally stratified layer at the top of the core.

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Transport properties of iron at Earth's core conditions: The effect of spin disorder

Cited by 24 publications

References 43 publications

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

Impurity Resistivity of fcc and hcp Fe-Based Alloys: Thermal Stratification at the Top of the Core of Super-Earths

Electrical resistivity of liquid Fe to 12 GPa: Implications for heat flow in cores of terrestrial bodies

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