Magnetic transition of iron carbide at high pressures

Abstract

High-pressure experiments and first-principles calculations were performed to investigate the compressibility and the magnetic properties of the iron carbide system, Fe 3C. The experimental data indicate that a significant reduction in volume occurs without any major structural changes at 55 GPa. Our calculations show that this reduction in volume corresponds to a magnetic collapse from the ferromagnetic to the non-magnetic state. The magnetic phase diagram of Fe 3C indicates that the non-magnetic state is stable under the conditions of the Earth's inner core. The equation of state for non-magnetic Fe 3C up to 400 GPa was also studied to assess this materials as a candidate as a major component of the Earth's inner core. The isothermal bulk modulus of non-magnetic Fe 3C at 0 K was found to be about twice as high as the experimental value of ferromagnetic Fe 3C. The density of non-magnetic Fe 3C is much lower than that in the inner core, as determined from the PREM model. This indicates that it is not possible that Fe 3C is a major component of the Earth's inner core.