title: Influence of lone pair doping on the multiferroic property of orthorhombic HoMnO3: ab initio prediction.
abstract: Using first principles density functional theory, we predict new multiferroic compounds Ho1/2A1/2MnO3 (A = As, Sb, Bi) with enhanced polarization. We find that doping of lone pair cations with different ionic radii, at the A-site of orthorhombic HoMnO3, results in a marked increase of the electronic polarization and its development along the b-axis. This development of electronic polarization along the b-axis is attributed to the breaking of the two-fold rotational symmetry which leads to the emergence of a polar b-axis. Furthermore, this symmetry breaking leads to the emergence of two inequivalent Mn ions (Mn(0) and Mn(1)) and the variance in their octahedral (Mn(0)O6 and Mn(1)O6) distortions. We rationalize the observed trends in the total polarization in terms of disparate eg electron hopping along the two different Mn(0) and Mn(1) chains. We expect large ionic polarization in the doped compounds due to the presence of 4s(2) As, 5s(2) Sb and 6s(2) Bi lone pairs, but surprisingly the effect of the lone pairs seems to be inactive. This is attributed to the strong GdFeO3 distortions exhibited by the MnO6 octahedron which hinders polar displacement of the lone pair cations.
authors.affiliation: Department of Physics, National Institute of Technology, Tiruchirapalli-620015, India.
authors.forename: Sathya Sheela
authors.initials: SS
authors.lastname: Subramanian
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Taisuke
authors.initials: T
authors.lastname: Ozaki
authors.forename: Tamio
authors.initials: T
authors.lastname: Oguchi
authors.forename: Baskaran
authors.initials: B
authors.lastname: Natesan