Electronic, magnetic and ferroelectric properties of multiferroic TlNiO₃: A first principles study

The ground state structural, electronic, magnetic and ferroelectric properties of TlNiO₃ are calculated by using density functional theory within the generalized gradient approximation. The calculations reveal that TlNiO₃ has an antiferromagnetic ground state with a direct band gap of 0.53 eV. The local magnetic moment of Ni(1) and Ni(2) are 1.735 μ_B and 0.809 μ_B, respectively. Plots of the density of states (DOS) exhibit hybridization of Ni(1), Ni(2)-3d, and O-2p states. However, the calculated charge density and electron localization function (ELF) show a largely ionic character of the Ni-O bonds which is also supported by the anomaly in the calculated Born effective charges (BECs) with respect to the corresponding nominal ionic charges. We also find a spontaneous polarization of 2.13 μC/cm² along the b-axis which is due to charge order induced by magnetic ordering.