Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                

Search for enhanced magnetism at the interface between Bi2Se3 and EuSe

K. Prokeš, Chen Luo, H. Ryll, E. Schierle, D. Marchenko, E. Weschke, F. Radu, R. Abrudan, V. V. Volobuev, G. Springholz, and O. Rader
Phys. Rev. B 103, 115438 – Published 25 March 2021
PDFHTMLExport Citation
Abstract
Authors
Article Text
  • INTRODUCTION
  • EXPERIMENTAL
  • RESULTS
  • DISCUSSION AND CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Enhanced magnetism has recently been reported for the topological-insulator/ferromagnet interface Bi2Se3/EuS with Curie temperatures claimed to be raised above room temperature from the bulk EuS value of 16 K. Here we investigate the analogous interface Bi2Se3/EuSe. EuSe is a low-temperature layered ferrimagnet that is particularly sensitive to external perturbations. We find that superconducting quantum interference device (SQUID) magnetometry of Bi2Se3/EuSe heterostructures reveals precisely the magnetic phase diagram known from EuSe, including the ferrimagnetic phase below 5 K, without any apparent changes from the bulk behavior. Choosing a temperature of 10 K to search for magnetic enhancement, we determine an upper limit for a possible magnetic coercive field of 3 mT. Using interface sensitive x-ray absorption spectroscopy we verify the magnetic divalent configuration of the Eu at the interface without contamination by Eu3+, and by x-ray magnetic circular dichroism (XMCD) we confirm at the interface the magnetic hysteresis obtained by SQUID. XMCD data obtained at 10 K in a magnetic field of 6 T indicate a magnetic spin moment of mz,spin=7μB/Eu2+, in good agreement with the SQUID data and the expected theoretical moment of Eu2+. Subsequent XMCD measurements in zero field show, however, that sizable remanent magnetization is absent at the interface for temperatures down to about 10 K.

    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    4 More
    • Received 9 June 2020
    • Accepted 11 March 2021

    DOI:https://doi.org/10.1103/PhysRevB.103.115438

    ©2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Magnetic orderSurface states
    1. Physical Systems
    Topological insulators
    1. Techniques
    X-ray absorption spectroscopyX-ray magnetic circular dichroism
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    K. Prokeš1,*, Chen Luo2,3, H. Ryll2, E. Schierle2, D. Marchenko2, E. Weschke2, F. Radu2, R. Abrudan2, V. V. Volobuev4,†, G. Springholz4, and O. Rader2

    • 1Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
    • 2Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
    • 3Fakultät für Physik, Technische Universität München, James-Franck-Straße 1, 85748 Garching bei München, Germany
    • 4Institute for Semiconductor and Solid State Physics, Johannes Kepler Universität, 4040 Linz, Austria

    • *prokes@helmholtz-berlin.de
    • †Present address: International Research Centre MagTop and Institute of Physics and Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02668 Warsaw, Poland

    Article Text (Subscription Required)

    Click to Expand

    References (Subscription Required)

    Click to Expand
    Issue

    Vol. 103, Iss. 11 — 15 March 2021

    Reuse & Permissions
    Access Options
    Author publication services for translation and copyediting assistance advertisement

    Authorization Required

    Log In
    Other Options
    ×

    Images

    • Figure 1
      Figure 1

      (a)–(d) Reflection high-energy electron diffraction recorded during the epitaxial growth of Bi2Se3/EuSe on the BaF2 substrates at a growth temperature of 260∘C evidencing a perfect 2D growth mode. (e) Atomic force microscopy image of the sample after deposition of four QL Bi2Se3. The corresponding surface profile is shown in (f) evidencing a flat surface exhibiting only quintuple layer steps with 1 nm step height.

      Reuse & Permissions
    • Figure 2
      Figure 2

      X-ray diffraction of four and eight QL epitaxial Bi2Se3 on EuSe. (a), (b) Reciprocal space maps recorded around the (2 2 2) and (0 0 0 15) reciprocal lattice points evidencing very sharp diffraction peaks for both EuSe and Bi2Se3 in the longitudinal (parallel to the surface) Q∥ direction, where Q is the scattering vector with a full width at half-maximum comparable to that of the substrate peak. The large broadening along the direction perpendicular to the surface Qz of the Bi2Se3 layer peak is due to the very small layer thicknesses of a few nm. (c), (d) Qz diffraction profiles of the eight QL Bi2Se3 sample, showing pronouced thickness oscillations around the Bi2Se3 peaks from which the layer thickness was derived. The lattice parameters were determined as a0=6.188 Å for EuSe (BaF2: a0=6.198 Å) and c=28.644 Å for the Bi2Se3 layer, both being essentially equal to the bulk lattice constants.

      Reuse & Permissions
    • Figure 3
      Figure 3

      Low-temperature detail of the temperature dependence of the magnetic susceptibility χ(T) = M(T)/H measured at 0.1 T and 2 T applied perpendicular and parallel to the surface of the sample with increasing and decreasing temperature. The temperature dependences of the inverse magnetic susceptibility measured in a field of 2 T with increasing temperature for both field orientations are shown in the inset. Full lines through experimental values represent best fits to a modified Curie-Weiss law.

      Reuse & Permissions
    • Figure 4
      Figure 4

      B-T magnetic phase diagram of Bi2Se3/EuSe for field applied perpendicular (a) and parallel (b) to the plane constructed from M(T)/H data as described in the main text. The magnetic susceptibility χ(T) = M(T)/H is color-coded: the blue (red) color denotes low (high) value of M(T)/H. AFM I, AFM II, FIM, FP, and Para denote the antiferromagnetic (↑↑↓↓), antiferromagnetic (↑↓), ferrimagnetic (↑↑↓), field polarized (↑↑), and paramagnetic phases, respectively. Open points denote positions of anomalies marking phase transitions.

      Reuse & Permissions
    • Figure 5
      Figure 5

      Field dependences of the magnetic moment per Eu atom measured using SQUID magnetometer at various temperatures between 2 K and 50 K in a wide field range applied perpendicular and parallel to the surface of the sample.

      Reuse & Permissions
    • Figure 6
      Figure 6

      X-ray absorption spectra of Bi2Se3/EuSe taken at 2 K using the VEKMAG instrument. The data confirm the Eu2+ spin configuration.

      Reuse & Permissions
    • Figure 7
      Figure 7

      X-ray absorption as a function of the applied magnetic field directed perpendicular to the surface of the Bi2Se3/EuSe sample taken at 2 K using the VEKMAG instrument at pre-edge (EiPE= 1117 eV), M5 (EiM5= 1129 eV) and M4 (EiM4= 1158 eV) energies as indicated by circles in Fig. 6.

      Reuse & Permissions
    • Figure 8
      Figure 8

      X-ray absorption as a function of the applied magnetic field directed perpendicular to the surface of the Bi2Se3/EuSe sample taken at 2 K, 6 K, and 11 K using the VEKMAG instrument at the M5 (EiM5= 1129 eV) edge using incident polarization σ+.

      Reuse & Permissions
    • Figure 9
      Figure 9

      Comparison between the magnetization curve as a function of the applied magnetic field obtained using SQUID and VEKMAG at 2 K. In the left inset we show the direct comparison between SQUID and VEKMAG relative signals. In the right inset we show the field derivative of both signals as a function of applied magnetic field.

      Reuse & Permissions
    • Figure 10
      Figure 10

      (a) X-ray absorption spectra of Bi2Se3/EuSe taken at 2 K using the VEKMAG instrument in an applied field of 6 T measured with opposite circular polarizations. Raw data without correction for the limited light polarization of 77% but after subtraction of a step function (Ref. [25]). (b) XAS spectrum averaged from σ+ and σ− data shown in (a) (left axis) and its energy integration (right axis). (c) XMCD calculated from data shown in (a) after correction for the light polarization of 77%. The data confirm the Eu2+ spin configuration.

      Reuse & Permissions
    • Figure 11
      Figure 11

      Comparison of the zero-field data (XUV instrument) to magnetic saturation (VEKMAG instrument) to derive an upper limit for the induced magnetic moment at the interface. (a) X-ray absorption spectra taken with positive σ+ (red broken line) and negative σ− (blue full line) circular polarization at 10 K in zero field using the XUV instrument. (b) XMCD, i. e., difference between the X-ray absorption spectra taken with positive σ+ and negative σ− circular polarization at 10 K in zero field using the XUV instrument (red solid line) along with the difference between the XAS taken with positive σ+ and negative σ− circular polarization obtained at 10 K under a magnetic field of 6 T using the VEKMAG instrument (blue dashed line, from Fig. 10). VEKMAG data have been shifted in energy to meet the energy scale of the XUV instrument due to the known small instrumental differences of the nominal energy scales of different beam lines. Energy scales in (a) and (b) are the same. Please note the multiplication ×100 for the zero-field data from the XUV instrument in (b).

      Reuse & Permissions
    ×

    Sign up to receive regular email alerts from Physical Review B

    Log In

    Cancel
    ×

    Search

    Article Lookup

    Paste a citation or DOI
    Enter a citation
    ×