Competition between the hcp nonmagnetic and antiferromagnetic phases in the transition path of Fe under pressure

Abstract

Density functional theory is applied to investigate the relative stability of Fe in different phases (bcc, fcc and hcp) for both the nonmagnetic (NM), ferromagnetic (FM) and anti-ferromagnetic (AFM) states as well as the effect of pressure. From the calculated enthalpy as a function of pressure, we predict the phase transition pathway for Fe at T = 0 K as: bcc (FM) (AFM2) → →→ hcp hcp (NM) (FM fcc ) 10GPa 30.2GPa 116GPa . A new intermediate, which is the hcp (AFM2) phase, was obtained. The resulting enthalpy of each phase indicates that the hcp AFM2 phase is more favorable than the hcp NM phase, thus we suggest the existence of novel transition under pressure from bcc FM to hcp AFM2 phase around 10 GPa. The calculated elastic constants Cij for the preferred pressure induced transition phases satisfy the criteria for elastic stability. Also these phases are dynamically stable based on the phonon dispersion and phonon total density of states consideration