Anomalous properties of hexagonal rare-earth ferrites from first principles

First-principles calculations are performed to predict structural, electric, magnetic, and magnetoelectric properties of hexagonal rare-earth ferrites (RFeO3) under chemical and hydrostatic pressures. Decreasing the rare-earth ionic radius has two dramatic consequences: (i) an enhancement of the electrical polarization by a factor of 60% and (ii) a magnetic transition, which renders the systems (weakly) ferromagnetic. Moreover and unlike conventional ferroelectrics, the electrical polarization strengthens as a hydrostatic pressure is applied and increases in magnitude in any hexagonal rare-earth ferrites. Finally, applying a hydrostatic pressure in RFeO3 having small or intermediate rare-earth ionic radius results in the sudden disappearance of a weak magnetization and of the linear magnetoelectric effect above some critical pressure. Origins of these striking effects are revealed.