First-principles study of pressure-induced magnetic transition in siderite FeCO3

The crystal structure, electronic configuration, spin state and electronic structure of siderite FeCO3 under pressure have been studied by first-principles calculations in the framework of density functional theory (DFT). The real antiferromagnetic (AFM) spin ordering state has been considered and the hydrostatic pressure condition is simulated. The calculated geometric structural data (unit-cell volume V, lattice constant a, cell angle α and atomic internal coordinate u) of FeCO3 at ambient condition in good agreement with available data from the literature. FeCO3 transforms from high spin (HS) AFM state to low spin (LS) nonmagnetic (NM) state between 40 and 50 GPa, concomitant with a volume collapse of 11%. The unit cell volume V0, bulk moduli B0, and its pressure derivative B′0 of the HS and LS state are fit with a 3rd-order Birch–Murnaghan equation of state, which consist well with available experimental results. The insulating nature of FeCO3 is remained after the magnetic transition. The 3d electrons of Fe2+ ions for the LS NM state are more localized than those of the HS AFM state, which leading to the magnetic transition.