title: Local distortions in multiferroic BiMnO3as a function of doping.
abstract: The structure of doped BiMnO3was studied using synchrotron x-ray powder diffraction. The dopants included isovalent magnetic and non-magnetic ions in the magnetic Mn sublattice (BiMn1-xMxO3withM=Cr, Fe and Ga), isovalent ions in the Bi sublattice (Bi0.9La0.1MnO3) and isovalent self-dopants (Bi0.95MnO2.925). The results indicate that at low doping levels, the orbitally ordered structure (C2/c(I)) of BiMnO3persists with strong Jahn-Teller distortions of two Mn1O6and Mn2O6octahedra (e.g. in BiMn0.95Ga0.05O3and Bi0.95MnO2.925); the distortion parameters of the Mn1O6and Mn2O6octahedra are noticeably smaller in BiMn0.95Ga0.05O3and Bi0.95MnO2.925than in BiMnO3. At higher doping levels, the orbitally disordered structure (C2/c(II)) of BiMnO3is realized with almost identical Mn-O bond lengths for one of the Mn1O6or Mn2O6octahedra (e.g. in BiMn0.85Cr0.15O3and BiMn0.85Fe0.15O3). BiMn0.85Fe0.15O3shows some anomalies in the distortion of the MnO6octahedra and in the magnetic properties. Rather strong Jahn-Teller distortions were found for both the Mn1O6and Mn2O6octahedra in Bi0.9La0.1MnO3. The Mn1O6and Mn2O6octahedra were compressed along one direction in Bi0.9La0.1MnO3whereas the octahedra were elongated in BiMnO3. Magnetic measurements indicate that Bi0.9La0.1MnO3adopts the orbitally disorderedC2/c(II) structure. The orbitally ordered state of BiMnO3was found to be very fragile to any type of doping. However, as long as the orbitally ordered phase persists, the ferromagnetic transition temperature remains almost the same.
authors.affiliation: International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Belik
keywords: BiMnO3; Jahn–Teller distortion; crystal structure; multiferroic