First-principles exploration of ferromagnetic and ferroelectric double-perovskite transition-metal oxides

Possible ferromagnetic and ferroelectric phases are explored for bismuth transition-metal oxides with double-perovskite structure A 2 BB ′ O 6 on the basis of first-principles calculations within the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). It is found that a lattice instability of the cubic to a non-centrosymmetric phase always happens in the all cases of lead and bismuth perovskite oxides with the 3d transition-metal ions at the B site. Placing bismuth ion at the A site in the double-perovskite structure, several sets of the 3d transition-metal ions are selected according to their total valence sum and the Goodenough–Kanamori rule for the superexchange coupling. Ferromagnetic solutions are actually obtained both within LSDA and GGA for Bi 2 CrFeO 6 , Bi 2 MnNiO 6 and Bi 2 CrCuO 6 . For non-centrosymmetric monoclinic Bi 2 MnNiO 6 , the ferromagnetic and ferroelectric phase has the spin magnetic moment of 5 μ B and the electric polarization of 28 μ C / cm 2 .