Magnetism in High-Pressure Iron

Orateur : Tommaso GORNI (IMPMC, Sorbonne Université-CNRS)

Due to the high pressures involved, the vast majority of iron contained in the Earth’s interior, from the upper mantle to the lower core, is found in the so-called "-Fe phase, displaying an hcp structure and a lack of macroscopic magnetization. However, in the pressure range of 15-30GPa, "-Fe presents several -ngerprints of an underlying magnetic state, among which superconductivity, believed to be mediated by antiferromagnetic uctuations. Firstprinciple simulations of paramagnetic and antiferromagnetic states both reproduce the experimental equation of state with a similar level of accuracy, whereas experimental evidence could not detect any magnetic splitting via Mossbauer spectroscopy on the one side, but suggested antiferromagnetic order via an anomalous Raman splitting on the other. Here, we perform a thorough re-investigation of the "-Fe antiferromagnetic states by Density Functional Theory calculations, and we map our results onto a spin model that we solve via a classical Monte Carlo approach. We -nally propose a new scenario where the long-range magnetic ordering is hampered by spins fuctuating in both amplitude and direction, as suggested by our fi-rst-principle calculations. Our results are supported by some very recent X-ray Emission Spectroscopy and Neutron Scattering data.

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