Magnetic-ion-induced displacive electric polarization in FeO5 bipyramidal units of (Ba,Sr)Fe12O19 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 Fe3+ (3d(5)) ions. Our simulations suggest that the competition between the long-range Coulomb interaction and short-range Pauli repulsion in a FeO5 bipyramidal unit with proper lattice parameters would favor an off-center displacement of Fe3+, which directly induces a local electric dipole. As a prototype example, we show that the electric dipole of a FeO5 bipyramid in (Ba,Sr)Fe12O19 hexaferrites leads to a different family of magnetic quantum paraelectrics. The manipulation of this unique magnetic-ion-induced displacive electric polarization in a FeO5 bipyramid could open up a promising route to generating unconventional dielectrics, ferroelectrics, and multiferroics.