Electronic spin transition of iron in the Earth's deep mantle

Abstract

Electronic spin is a quantum property of every electron, associated with its intrinsic angular momentum. Though there are no suitable physical analogies to describe the spin quantum number, there are two possibilities, called spin ‘up’ and spin ‘down.’ The electronic structure of iron in minerals is generally such that valence electrons will more abundantly occupy different spatial orbitals and maintain the same spin than occupy the same spatial orbital and assume opposite spin, called ‘spin‐paired.’To the astonishment of mineral physicists, pressure‐induced electronic spin‐pairing transitions of iron that were predicted nearly 50 years ago recently have been detected in major mantle‐forming oxides and silicates in ultrahigh‐pressure experiments at lower‐mantle pressures [e.g., Badro et al., 2003, 2004; Lin et al., 2005]. If such a spin transition is occurring in the Earth's lower mantle, there may be profound geophysical implications.