Mantle minerals are among the most complex alloys, involving strongly
correlated magnetic end members. Outstanding examples are the most
abundant phases of the Earth's lower mantle (Mg(1-x),Fex)SiO3-perovskite and (Mg(1-y),Fey)O,
magnesiumwustite. An additional complication is the change in magnetic
state of iron under pressure in certain sites. High-to-low spin
transitions in iron are found in these minerals at pressures corresponding
to mid-mantle. They alter the partitioning of Fe between them, most likely
increasing y/x. But the transition pressure is concentration dependent
providing a negative feedback to the spin transition. Understanding this
complex phenomenon is fundamental to understanding the nature of the lower
mantle. The first step is to address two classes of materials problems:
solid solutions and the behavior of the strongly correlated iron sites
under pressure. The next step involves phase equilibrium, thermoelastic,
and transport properties for single and multi-phase aggregates.
