Multiferroic Compounds with Double-Perovskite Structures.

New multiferroic compounds with double-perovskite structures were synthesized. Bi₂NiMnO₆ was synthesized in bulk form by high-pressure synthesis and also in a thin-film form by epitaxial growth. The material showed both ferromagnetic and ferroelectric properties, i.e., the multiferroic property at low temperature. Bi₂FeCrO₆ was also fabricated in a (1 1 1) oriented BiFeO₃/BiCrO₃ artificial superlattice, with a 1/1 stacking period. The superlattice film showed ferromagnetic behavior and polarization switching at room temperature. In the compounds, Bi ion, located at the A site in the perovskite structure, caused ferroelectric structural distortion, and the B-site ordering of the Ni and Mn ions (Fe and Cr ions) in a rock-salt configuration led to ferromagnetism according to the Kanamori-Goodenough rule.