First-principles study on the differences of possible ferroelectric behavior and magnetic exchange interaction between Bi2NiMnO6 and La2NiMnO6

The differences of possible ferroelectric behavior and magnetic exchange interaction between Bi2NiMnO6 and La2NiMnO6 have been investigated by first-principles calculation. Paying attention to the electronic structures, bonding interaction, and Born effective charges of the two compounds, the calculations reveal that ferroelectric distortion occurs only in Bi2NiMnO6 rather than La2NiMnO6. The calculation also indicates that the Ni-Mn ferromagnetic exchange interaction is weakened in Bi2NiMnO6 compared with that in La2NiMnO6. Thus the present work explains why Bi2NiMnO6 has a lower Curie temperature compared with La2NiMnO6. The mechanism why Bi2NiMnO6 has weaker Ni-Mn ferromagnetic exchange interaction than La2NiMnO6 is explored by considering the Kugel-Khomskii model. Finally, the electric polarizations of Bi2NiMnO6 with ferromagnetic and ferrimagnetic order are estimated to be 18.05 and 19.01 μC/cm2, respectively, indicating the anomaly of electric polarization near the Curie temperature of Bi2NiMnO6.