AGU: Geophysical Research Letters

 

Editors' Highlight

Electron spin transitions in lower mantle minerals

Understanding the high-pressure behavior of ferropericlase (Mg,Fe)O, likely the second most abundant mineral in the Earth's lower mantle, is important for modeling the chemistry and physics of the lower mantle. Previous experiments have shown that ferropericlase undergoes an electron spin transition at high pressures. Noting that the abundance of iron or manganese in the (Mg,Fe)O determines the pressure at which spin transitions occur, Fei et al. (2007) conducted high-pressure laboratory experiments on ferropericlase to better classify its behavior at lower mantle depths. They found that the pressure-induced spin transition in (Mg,Fe)O solid solutions results in a volume contraction at the spin crossover pressure because of the reduction in the Fe+2 ionic radius at its low-spin state. The required transition pressure increases linearly with increasing FeO content. The authors also developed equations to determine the changes in bulk modulus seen at this transition, dependent on iron content. They anticipate that such data can be used to better model mantle dynamics, and expect that the existence of low-spin ferropericlase implies that the lower mantle might be denser than previously thought.

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