Pressure-induced electronic spin transition of iron in magnesiowustite-(Mg,Fe)O

An electronic transition of iron in magnesiowustite has been studied with synchrotron Mossbauer and x-ray emission spectroscopies under high pressures. Synchrotron Mossbauer studies show that the quadrupole splitting disappears and the isomer shift drops significantly across the spin-paring transition of iron in (Mg-0.75,Fe-0.25)O between 52 and 70 GPa. Based upon current results and percolation theory, we reexamine the high-pressure phase diagram of (Mg,Fe)O and find that iron-iron exchange interaction plays an important role in stabilizing the high-spin state of iron in FeO-rich (Mg,Fe)O.