Spin transition of iron in magnesiowüstite in the Earth's lower mantle

Abstract

Iron is the most abundant transition-metal element in the mantle and therefore plays an important role in the geochemistry and geodynamics of the Earth's interior. Pressure-induced electronic spin transitions of iron occur in magnesiowüstite, silicate perovskite and post-perovskite. Here we have studied the spin states of iron in magnesiowüstite and the isolated effects of the electronic transitions on the elasticity of magnesiowüstite with in situ X-ray emission spectroscopy and X-ray diffraction to pressures of the lowermost mantle. An observed high-spin to low-spin transition of iron in magnesiowüstite results in an abnormal compressional behaviour between the high-spin and the low-spin states. The high-pressure, low-spin state exhibits a much higher bulk modulus and bulk sound velocity than the low-pressure, high-spin state; the bulk modulus jumps by approximately 35 percent and bulk sound velocity increases by approximately 15 percent across the transition in (Mg0.83,Fe0.17)O. Although no significant density change is observed across the electronic transition, the jump in the sound velocities and the bulk modulus across the transition provides an additional explanation for the seismic wave heterogeneity in the lowermost mantle. The transition also affects current interpretations of the geophysical and geochemical models using extrapolated or calculated thermal equation-of-state data without considering the effects of the electronic transition.

Reversible mechanism for spin crossover in transition-metal cyanides

“…[6][7][8] ) for which Fe II exhibits a high-spin (S = 2) configuration at ambient pressure. In fact, for CoFe-PBA, the high-spin Fe II is of significantly higher energy (1.94 eV/fu) than the LS-Fe II (S = 0).…”

“…1,2,12,13 However, neither the microscopic transition mechanisms nor the effects of Fe-vacancies, water, and alkali metals on these mechanisms are completely understood, despite considerable experimental and theoretical effort. [16][17][18][19] 6 ] does not influence the charge transfer excitation energy. 23 Here we investigate the microscopic spin transition mechanisms via an ab initio lattice model for CoFe-PBA.…”

“…Spin crossover generally occurs in octahedrally coordinated 3d transition metal complexes, and can be induced by external perturbations in various forms [1][2][3][4][5][6][7][8][9][10] by tuning the competing intra-atomic exchange energy (Hund's coupling), and the crystal field energy. Such spin transitions are observed in molecular-based magnets, [1][2][3][4][5] oxides, 6-8 supra-molecular systems, 9 and metal-organic complexes, 11 which show promising application capabilities in sensors, switches, and recording devices.…”

Pressure-induced Jahn-Teller suppression and simultaneous high-spin to low-spin transition in the layered perovskiteCsMnF4

“…[2][3][4] Similar to Earth's interior conditions, high-pressure techniques have emerged as efficient tools to attain structural conditions for spin change, even dealing with systems where ⌬Ӷ⌬ SCO . Although we know the relevance of the spin state of Fe 2+ in ͑Mg,Fe͒O, the second most abundant phase in lower mantle, on the radiative conductivity 5,6 or that highspin Fe 3+ ͑S =5/2͒ transits to the low-spin state ͑S =1/2͒ in Fe 2 O 3 at pressures around 50 GPa, 7,8 the problem of predicting spin-crossover pressures in materials science is still a challenge. A comprehensive characterization of high-spin to low-spin ͑or intermediate spin͒ 1 phenomena requires knowledge of the electronic structure of materials, a major problem because optical absorption measurements in extreme conditions are tricky.…”

“…Spin-transition phenomena have been intensively investigated in materials providing ligand fields close to the spin crossover. [1][2][3][4][5][6][7][8][9] Current research of this kind is focused on materials involving transition-metal complexes with C, O, or N ligands. Their strong neuphelaxetic effect makes those complexes well suited to exhibiting bistability around ambient conditions.…”