Magnetic-ion-induced displacive electric polarization in Fe O sub(5) bipyramidal units of (Ba, Sr) Fe sub(12)O sub(19) hexaferrites

Electric polarization in conventional paraelectric/ferroelectric oxides usually involves the displacement of nonmagnetic transition-metal ions with an empty d shell. Here we unravel an unusual mechanism for electric polarization based on the displacement of magnetic Fe super(3+) (3d super(5)) ions. Our simulations suggest that the competition between the long-range Coulomb interaction and short-range Pauli repulsion in a FeO sub(5) bipyramidal unit with proper lattice parameters would favor an off-center displacement of Fe super(3+), which directly induces a local electric dipole. As a prototype example, we show that the electric dipole of a FeO sub(5) bipyramid in (Ba, Sr) Fe sub(12)O sub(19) hexaferrites leads to a different family of magnetic quantum paraelectrics. The manipulation of this unique magnetic-ion-induced displacive electric polarization in a FeO sub(5) bipyramid could open up a promising route to generating unconventional dielectrics, ferroelectrics, and multiferroics.