Iron spin state in silicate perovskite at conditions of the Earth's deep interior

Abstract

We present a review of our recent work concerning the spin state of Fe2+ and Fe3+ in iron magnesium aluminium silicate perovskite, the most abundant phase in the Earth's interior. Experimental results obtained using Mössbauer spectroscopy (with a radioactive source and a Synchrotron Mössbauer Source) and nuclear forward scattering for a range of different sample compositions in both externally heated and laser-heated diamond anvil cells show clear trends in the variation of hyperfine parameters with pressure and temperature. These trends combined with reported total spin state measurements using X-ray emission spectroscopy on samples of similar composition support the conclusion that Fe2+ undergoes a high-spin to intermediate-spin transition near the top of the lower mantle and an intermediate-spin to low-spin transition near the bottom of the lower mantle. No spin transition is observed to occur in Fe3+ for samples with compositions relevant for the lower mantle.