Research ArticleAPPLIED PHYSICS

Interface reconstruction with emerging charge ordering in hexagonal manganite

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Science Advances  18 May 2018:
Vol. 4, no. 5, eaar4298
DOI: 10.1126/sciadv.aar4298
  • Fig. 1 (S)TEM images showing the interface between the YMnO3 film and sapphire substrate.

    (A) Low-magnification bright-field TEM image for the YMnO3 film. (B) HAADF image showing the interface between the YMnO3 film and Al2O3 substrate from the [210] zone axis. The atomic model of YMnO3 at the [210] zone axis is embedded. Y ions are in green, Mn ions are in purple, and O ions are in red. The reconstructed interfacial layer is highlighted in a red dashed rectangle. (C) Integrated intensity profile from top to bottom in the blue rectangle area in (B). The interfacial Y-Mn-Mn layer is shown between two red vertical lines. a.u., arbitrary units. (D) HAADF image for the interface taken at the [110] zone axis. (E) The corresponding integrated intensity profile from blue rectangle area in (D).

  • Fig. 2 ABF images and atomically resolved EELS results acquired from the interfacial areas.

    (A) ABF image showing the interface between the YMnO3 film and Al2O3 substrate from the [210] zone axis. The white arrow shows the EELS line-scan direction. The sequential numbers for MnO layers are indicated. Scale bar, 1 nm. Atomic models for YMnO3, interfacially reconstructed MnO double layer, and Al2O3 are embedded. The interface is marked by a horizontal red line. (B) ABF image acquired from the [110] zone axis. Atomic models from the [110] zone axis are overlaid, with Al, Y, Mn, and O atoms shown in blue, green, purple, and red, respectively. Scale bar, 1 nm. (C) Mn L2,3 edges extracted from EELS line-scan results across the interface. The chemical shift can be indicated by the gray dashed line. (D) Evolution of L2,3 ratios and the corresponding valence states of Mn ions.

  • Fig. 3 Optimized ground state structure of [(YMnO3)/(YMn2O4)]√3×√3×2 superlattice, with a positive Psl along with ST1 and CO3 arrangements (see text).

    (A and B) Atomic model viewing from the [110] and [210] directions, respectively. Δ1 and Δ2 indicate the relative displacements of Y ions along the c-axis direction, whereas θ1, θ2, and θ3 represent the angles that MnO5 tilt away from the c axis in different layers (see the Supplementary Materials). The hollow blue and pink arrows show the directions of the polarization in the MnO single layers and MnO double layers, respectively. (C and D) Atomic model of MnO double layers, with the Mn-Otp bond lengths being indicated in black numbers (in Å). The black arrows indicate the relative displacements of Y and O ions in these two latter panels.

  • Fig. 4 Initial structures and charge order configurations used in our DFT calculations.

    (A) Schematics of the stacking rule. Y ions should be sandwiched along the c axis between two O ions belonging to adjacent (001) Mn-O layers. The vertical alignment of Y and these O ions are marked by dashed blue lines. The cyan rectangle marks half of the superlattice, which is then shown in the remaining panels of this figure. (B and C) ST1 and ST2 structures, respectively. (D to G) CO types ranging from CO1 to CO4, respectively, in the MnO double layers. Note that the polarization of the single YMnO3 layer is set to be pointing up in all configurations, as indicated by the blue arrow. The direction of the polarization induced by CO in the MnO double layers is indicated by pink arrows. The green and purple spheres depict the nominal Mn2+ and Mn3+ ions, respectively.

  • Fig. 5 Schematization of the 3d orbital occupancy and structural features of MnO versus FeO double layers.

    (A and B) 3d orbital occupancy for Mn3+ and Mn2+, respectively. (C) Bond and antibond states between Otp,2− and Mn3+. (D) Bond and antibond states involving the Mn2+, Fe3+, and Fe2+ ions, respectively. (E and F) Schematics of the noncentrosymmetric MnO and centrosymmetric FeO double layers, respectively. Small red spheres are O ions, whereas green, purple, and golden spheres are Mn2+, Mn3+, and Fe2+/Fe3+, respectively. Superscript numbers on Fe or Mn ions indicate the nominal valence states.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/5/eaar4298/DC1

    Supplementary Materials

    fig. S1. Schematic atomic models.

    fig. S2. Quantitative evaluation of polarization in the film.

    fig. S3. EDS mapping results for the interface.

    fig. S4. ABF images from the interfacial and the bulk areas.

    fig. S5. Calculated YMnO3 polarization dependence of CO in MnO double layers.

    References (35, 36)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials
    • fig. S1. Schematic atomic models.
    • fig. S2. Quantitative evaluation of polarization in the film.
    • fig. S3. EDS mapping results for the interface.
    • fig. S4. ABF images from the interfacial and the bulk areas.
    • fig. S5. Calculated YMnO3 polarization dependence of CO in MnO double layers.
    • References (35, 36)

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