Spin crossover in ferropericlase from first-principles molecular dynamics

Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of the Earth's lower mantle. With increasing pressure, the Fe ions in the material begin to collapse from a magnetic to non-magnetic spin state. We present a finite-temperature first-principles phase diagram of this spin crossover, finding a broad pressure range with coexisting magnetic and non-magnetic ions due to favorable enthalpy of mixing of the two. Furthermore, we find the electrical conductivity of the mineral to reach semi-metallic values inside the Earth.