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Local distortions in multiferroic BiMnO3 as a function of doping

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Author(s): Alexei A Belik

Journal: Science and Technology of Advanced Materials
ISSN 1468-6996

Volume: 12;
Issue: 4;
Start page: 044610;
Date: 2011;
Original page

ABSTRACT
The structure of doped BiMnO3 was studied using synchrotron x-ray powder diffraction. The dopants included isovalent magnetic and non-magnetic ions in the magnetic Mn sublattice (BiMn1−xMxO3 with M=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 BiMnO3 persists with strong Jahn–Teller distortions of two Mn1O6 and Mn2O6 octahedra (e.g. in BiMn0.95Ga0.05O3 and Bi0.95MnO2.925); the distortion parameters of the Mn1O6 and Mn2O6 octahedra are noticeably smaller in BiMn0.95Ga0.05O3 and Bi0.95MnO2.925 than in BiMnO3. At higher doping levels, the orbitally disordered structure (C2/c(II)) of BiMnO3 is realized with almost identical Mn–O bond lengths for one of the Mn1O6 or Mn2O6 octahedra (e.g. in BiMn0.85Cr0.15O3 and BiMn0.85Fe0.15O3). BiMn0.85Fe0.15O3 shows some anomalies in the distortion of the MnO6 octahedra and in the magnetic properties. Rather strong Jahn–Teller distortions were found for both the Mn1O6 and Mn2O6 octahedra in Bi0.9La0.1MnO3. The Mn1O6 and Mn2O6 octahedra were compressed along one direction in Bi0.9La0.1MnO3 whereas the octahedra were elongated in BiMnO3. Magnetic measurements indicate that Bi0.9La0.1MnO3 adopts the orbitally disordered C2/c(II) structure. The orbitally ordered state of BiMnO3 was 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.

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