title: Electric polarization, magnetoelectric effect, and orbital state of a layered iron oxide with frustrated geometry.
abstract: A layered iron oxide RFe2O4 (R denotes rare-earth-metal elements) is an exotic dielectric material with charge-order (CO) driven electric polarization and magnetoelectric effect caused by spin-charge coupling. In this paper, a theory of electronic structure and dielectric property in RFe2O4 is presented. Charge frustration in paired-triangular lattices allows a charge imbalance without inversion symmetry. Spin frustration induces reinforcement of this polar CO by a magnetic ordering. We also analyze an orbital model for the Fe ion which does not show a conventional long-range order.
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Nagano
authors.forename: M
authors.initials: M
authors.lastname: Naka
authors.forename: J
authors.initials: J
authors.lastname: Nasu
authors.forename: S
authors.initials: S
authors.lastname: Ishihara