Magnetic transition in compressed Fe3C from x-ray emission spectroscopy

The magnetic properties of iron in cementite (Fe3C) have been measured by x-ray emission spectroscopy in a diamond cell up to 45 GPa. The Fe-K-beta fluorescence peaks reveal that Fe3C undergoes a magnetic collapse at approximately 25 GPa, consistent with theoretical predictions. This transition is likely to be a second-order phase transition without a major structural change. The magnetic collapse transition is expected to affect the elastic and thermodynamic properties of Fe3C; the nonmagnetic phase predicted theoretically has a higher incompressibility and density than the magnetic state. Our results support recent theoretical and thermodynamic calculations indicating that Fe3C is unlikely to be the major component in the Earth's inner core.