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  • Title: Spin transition zone in Earth's lower mantle.
    Author: Lin JF, Vankó G, Jacobsen SD, Iota V, Struzhkin VV, Prakapenka VB, Kuznetsov A, Yoo CS.
    Journal: Science; 2007 Sep 21; 317(5845):1740-3. PubMed ID: 17885134.
    Abstract:
    Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.
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