Research ArticlePHYSICS

Natural van der Waals heterostructural single crystals with both magnetic and topological properties

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Science Advances  15 Nov 2019:
Vol. 5, no. 11, eaax9989
DOI: 10.1126/sciadv.aax9989
  • Fig. 1 Magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n.

    (A to D) Schematics of the evolution of the heterostructures. The arrows show the spin orientation of Mn with black pointing down and white pointing up. The question marks in (C) and (D) show the uncertainty of the spin orientations due to complex magnetic interactions. (E to H) Atomic resolution high-angle annular dark-field (HAADF)–STEM images of the compounds displayed in (A) to (D). The images are taken along a zone axis perpendicular to the c axis. QL stands for quintuple layer and SL stands for septuple layer. (I to L) Selected-area electron diffraction (SAED) patterns of the compounds shown in (A) to (D).

  • Fig. 2 XRD patterns of single crystals.

    (A) MnBi2Te4. (B) MnBi4Te7. The measurement was performed on single-crystalline pieces (shown in the insets) with only the a-b plane exposed to x-ray. The insets also show the structure models based on SL and QL van der Waals layers. a.u., arbitrary units.

  • Fig. 3 Magnetic properties of MnBi2Te4 and MnBi4Te7 single crystals.

    (A to C) Magnetic susceptibility and magnetization of MnBi2Te4. The parameters θ and μeff are the Curie-Weiss temperature and effective moment, respectively. (D to F) Magnetic susceptibility and magnetization of MnBi4Te7 at high fields. (G to I) Magnetic susceptibility and magnetization of MnBi4Te7 at low fields. The black arrows with dotted lines in (I) show the sweep directions of the magnetic field. The heterostructures and spin structures are schematically shown as insets in (B), (C), (E), (F), and (I).

  • Fig. 4 DFT band structures of MnBi4Te7.

    (A) Bulk band structure without SOC. (B) Bulk band structure with SOC. (C) Band structure of a QL-terminated five–van der Waals layer slab. (D) Band structure of an SL-terminated seven–van der Waals layer slab. The calculations were performed assuming an AFM ground state. The thickness of the band is proportional to the contribution of the indicated atoms (A and B) or van der Waals layers [QL/SL in (C) and (D)].

  • Fig. 5 Surface band structure of MnBi4Te7 at a photon energy of 48 eV.

    (A and C) Measured SS along the Γ¯M¯ direction at 20 and 300 K, respectively. The intensity plots are symmetrized with respect to the center lines and averaged. (B and D) The energy distribution curves extracted from the intensity maps of (A) and (C), respectively, in the range of −0.24 Å−1 < kx < 0.24 Å−1. The intensity at the Γ¯ point is shown in red. The DP in (B) and (D) is short for Dirac point.

  • Fig. 6 Anomalous electrical transport properties and magnetic structures of MnBi4Te7 single crystals.

    (A) AH resistivity. The black arrows with dashed-dotted lines show the sweep directions of the magnetic field. The inset shows the total Hall resistivity at 2 K. (B) AH conductivity below 2 K. The central-symmetric data including background noise are due to the analysis method (see the Supplementary Materials). (C) Temperature dependence of AH conductivity and magnetic susceptibility measured at 1 T. The inset shows the temperature dependence of the scaling factor. (D) Field- and temperature-dependent magnetoresistance above 2 K. (E) Field- and temperature-dependent magnetoresistance below 1 K. (F) Temperature and field dependence of magnetic structures when the field is swept from a negative field to a positive field. Note that measurements above 2 K and below 1 K are on two pieces of samples. The magnetic field is applied along the c axis for all the transport properties measurements.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax9989/DC1

    Section S1. Data analysis methods for electrical transport measurements

    Fig. S1. Crystal structures and XRD patterns.

    Fig. S2. Additional STEM data.

    Fig. S3. Additional surface characterization.

    Fig. S4. Magnetization of polycrystalline samples.

    Fig. S5. Additional physical properties of MnBi4Te7 single crystals.

    Fig. S6. Additional information for the magnetization of MnBi4Te7 single crystals.

    Fig. S7. Additional physical properties of MnBi2Te4 single crystals.

    Fig. S8. Magnetization dependence of ρyxA for MnBi4Te7 single crystals.

    Fig. S9. Additional electrical transport properties below 1 K for MnBi4Te7 single crystals.

    Table S1. Crystal structure parameters of Mn-Bi-Te compounds.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Data analysis methods for electrical transport measurements
    • Fig. S1. Crystal structures and XRD patterns.
    • Fig. S2. Additional STEM data.
    • Fig. S3. Additional surface characterization.
    • Fig. S4. Magnetization of polycrystalline samples.
    • Fig. S5. Additional physical properties of MnBi4Te7 single crystals.
    • Fig. S6. Additional information for the magnetization of MnBi4Te7 single crystals.
    • Fig. S7. Additional physical properties of MnBi2Te4 single crystals.
    • Fig. S8. Magnetization dependence of ρyxA for MnBi4Te7 single crystals.
    • Fig. S9. Additional electrical transport properties below 1 K for MnBi4Te7 single crystals.
    • Table S1. Crystal structure parameters of Mn-Bi-Te compounds.

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