The preparation, and structural and multiferroic properties of B-site ordered double-perovskite Bi₂FeMnO₆

We report the structural, magnetic, and ferroelectric properties of double-perovskite Bi₂FeMnO₆ in which Fe³⁺ and Mn³⁺ cations are present with alternative ordering along the [111] direction. High-flux synchrotron X-ray diffraction and high resolution transmission electron microscopy show that the pseudo-cubic lattice of Bi₂FeMnO₆ consists of alternatively corner-shared octahedra of FeO₆ and MnO₆. In the highly ordered Bi₂FeMnO₆ thin films, the unusual spin-glassy magnetic state is observed below 18 K by a superconducting quantum interference device, and this is ascribed to the magnetic frustration at the [111] Fe³⁺ and Mn³⁺ planes as indicated by X-ray magnetic circular dichroism measurements. Combining with the orbital model analysis based on Goodenough-Kanamori-Anderson rules, first-principles calculations and Monte Carlo simulations suggest that magnetic frustration is dominated by the long-range second nearest neighboring antiferromagnetic interactions of Fe³⁺-Fe³⁺ and Mn³⁺-Mn³⁺ and leads to the surprisingly weak magnetism. On the other hand, robust room-temperature ferroelectricity in Bi₂FeMnO₆ films is confirmed by piezoelectric force microscopy through electrically switching the polarization state and the ferroelectric retention.