dr. Andreas Scaramucci: Structure and Magnetic Order in Multiferroic YBaFeCuO5

Abstract

Using density functional theory, we investigate the structure and magnetic ordering of the bilayered perovskite multiferroic YBaFeCuO₅ (YBFCO). We calculate energies of configurations with various Fe³⁺/Cu²⁺ ordering in the YBFCO structure. We find a set of configurations characterized by a specific correlation of Fe³⁺ and Cu²⁺ positions, which have energies close to the ground state. The exchange coupling constants for these configurations are compatible with the high-temperature commensurate magnetic ordering but do not explain the experimentally observed low-temperature incommensurate order. Finally, we propose a new mechanism, based on the particular type of magnetic cation disorder in YBFCO, which can induce spin spiral states.