Magnetism and phase transitions of iron under pressure

The spin-polarized generalized gradient approximation within the plane-wave pseudopotential density functional theory is employed to investigate the magnetism and phase transition of iron under pressure. It is found that iron has a ferromagnetic body-centered-cubic (bcc) ground state, while at high pressure (such as at the Earth's lower mantle and core pressure), the most stable phase is the nonmagnetic hexagonal-close-packed (hcp) phase. For the face-centered-cubic (fcc) iron, we find that there is an intermediate-spin state (IS) during the transformation from the high-spin state (HS) to the low-spin (LS) state under pressure. The transition pressures of the HS → IS and the IS → LS are about 15 GPa and 50 GPa, respectively. The magnetism can affect the properties of iron up to 72.9 GPa. From the enthalpy difference between every two phases, we find the phase transition pressures of FM-bcc → FM-hcp, FM-bcc → NM-hcp and NM-bcc → NM-hcp are 14.4 GPa, 29.5 GPa and 42.7 GPa, respectively.