Thermal-Induced Evolution of Magnetic Properties of FeO₂ Under High Pressures

Pyrite-type FeO₂ is a crystalline compound that is the stable form of iron oxide in the pressure range of ~80 GPa to over 200 GPa. Here, we have performed density functional theory (DFT) calculations on this system using the GGA+U exchange-correlation functional, principally along the ρ = 7.1 g/cm³ isochore up to temperatures above 3500 K (corresponding to the Earth’s lowermost-mantle conditions), to explore the evolution of the magnetic properties under thermal effects. The DFT results suggest a magnetic state transition induced by temperature at ~1000 K. The behavior of the electronic properties such as thermal and electric conductivity, and thermodynamic properties such as specific heat have been explored with regard to the change of magnetic states in FeO₂.