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arxiv: 2508.15527 · v2 · submitted 2025-08-21 · ❄️ cond-mat.mtrl-sci

NMR evidence for an antisite-induced magnetic moment on Bi in a topological insulator heterostructure MnBi₂Te₄/(Bi₂Te₃)_n

R. Kalvig , E. Jedryka , A. Lynnyk , P. Skupinski , K. Grasza , M. Wojcik This is my paper

Pith reviewed 2026-05-18 21:50 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords topological insulatorheterostructureNMR spectroscopyMnBi2Te4Bi2Te3antisite defectsinduced magnetic momentquantum anomalous Hall effect
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The pith

NMR measurements show Mn antisites induce an antiparallel magnetic moment on Bi atoms in a MnBi2Te4/(Bi2Te3)n heterostructure.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The work examines the low-temperature magnetic structure of a self-organized MnBi2Te4/(Bi2Te3)n crystal using 55Mn and 209Bi NMR together with bulk magnetization. Signals recorded while sweeping the out-of-plane field through the antiferromagnetic to canted-antiferromagnetic spin-flop transition reveal the presence of Mn atoms on wrong lattice sites. These antisites are antiferromagnetically coupled to the regular Mn layers and create a local antiparallel moment on neighboring Bi atoms in the host layers. The resulting bismuth moment supplies an extra ferromagnetic component. This local picture clarifies how defects shape the net magnetism that is relevant for tuning the quantum anomalous Hall effect in such heterostructures.

Core claim

In the MnBi2Te4/(Bi2Te3)n heterostructure grown from an off-stoichiometric melt, field-dependent 209Bi NMR at 4.2 K directly registers an antiparallel magnetic moment on Bi atoms that is induced by antiferromagnetically coupled Mn antisites; this moment contributes a distinct ferromagnetic component in addition to the canted antiferromagnetic order of the Mn layers, with the canting angle itself extracted from the NMR shifts across the spin-flop transition up to 6 T.

What carries the argument

The 209Bi NMR resonance that tracks the hyperfine field arising from the antiparallel moment on bismuth atoms neighboring Mn antisites.

If this is right

  • The extra ferromagnetic component from Bi modifies the net magnetization and the details of the spin-flop transition in the heterostructure.
  • Engineering the density of Mn antisites offers a handle on the overall magnetic interactions between layers.
  • The canting angle of Mn moments at any given field can be read directly from the NMR line positions.
  • Device-level optimization of the quantum anomalous Hall effect must incorporate the contribution of this defect-induced Bi moment.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Local spectroscopic signatures of induced moments on nominally non-magnetic atoms may be common in other defect-containing magnetic topological insulators and could be searched for with similar NMR or muon techniques.
  • Heterostructure growth protocols that minimize antisites might suppress the unwanted ferromagnetic channel and raise the temperature window for quantum anomalous Hall transport.
  • Theoretical models of the magnetic phase diagram should include the Bi sublattice moment as an additional degree of freedom when predicting edge-state behavior.

Load-bearing premise

The observed 209Bi NMR signal is produced by bismuth atoms carrying a moment induced by nearby Mn antisites rather than by other lattice defects or experimental artifacts.

What would settle it

If NMR spectra taken on a control crystal engineered with substantially lower Mn antisite density show the same 209Bi resonance frequency and field dependence, the assignment of the signal to the antisite-induced Bi moment would be ruled out.

Figures

Figures reproduced from arXiv: 2508.15527 by A. Lynnyk, E. Jedryka, K. Grasza, M. Wojcik, P. Skupinski, R. Kalvig.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
read the original abstract

MnBi$_2$Te$_4$ (MBT) is the first intrinsic magnetic topological insulator, combining a topologically protected surface metallic state and intrinsic magnetic order. A structural compatibility with the nonmagnetic Bi$_2$Te$_3$ (BT) parent compound gives a possibility to create MBT/BT heterostructures and manipulate their magnetic state in view of optimizing the Quantum Anomalous Hall Effect (QAHE). In this work an extensive Nuclear Magnetic Resonance (NMR) study, supported by the bulk magnetization measurements has been performed at 4.2 K on a self-organized single crystal MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$_n$ heterostructure, obtained from the Mn$_{0.81}$Bi$_{2.06}$Te$_{4.13}$ melt. $^{55}$Mn and $^{209}$Bi NMR signals have been recorded as a function of the out-of-plane magnetic field up to 6 T, covering a spin-flop transition (SFT) from the antiferromagnetic (AFM) to the canted antiferromagnetic (CAFM) configuration of the Mn layers. The canting angle at different external field values has been estimated based on NMR data. Presence of the AFM-coupled Mn antisites has been evidenced and shown to induce an antiparallel magnetic moment on Bi atoms within the host Bi layer. Detection of the induced magnetic moment on bismuth which contributes a new ferromagnetic (FM) component is of utmost importance for understanding the magnetic interactions in the MBT/BT system. These findings have potentially important implications for engineering the QAHE devices.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports an extensive 55Mn and 209Bi NMR study at 4.2 K on a self-organized MnBi2Te4/(Bi2Te3)n heterostructure crystal, combined with bulk magnetization data. Signals are tracked versus out-of-plane field up to 6 T across the AFM-to-CAFM spin-flop transition; the canting angle is extracted from the Mn data, and a 209Bi resonance is assigned to an antiparallel moment on Bi atoms induced by AFM-coupled Mn antisites, thereby adding a new FM component to the magnetic interactions.

Significance. If the Bi-moment assignment is robust, the result would be significant for magnetic topological insulators: it identifies an additional local-moment channel that could influence the net magnetization and surface-state properties relevant to QAHE optimization in MBT/BT heterostructures. The field-dependent NMR approach across a well-defined transition is a methodological strength.

major comments (2)
  1. [Abstract] Abstract and implied results: the central claim that the observed 209Bi resonance arises specifically from Mn-antisite-induced antiparallel Bi moments is load-bearing, yet the manuscript provides no quantitative hyperfine-field fits, error bars, or raw spectra to demonstrate that this assignment is unique versus signals from regular Bi sites in MBT or BT layers.
  2. [NMR data analysis (implied)] The extraction of the canting angle from Mn NMR and its use to interpret the Bi signal assumes a known hyperfine coupling constant for the antisite-induced Bi environment; without explicit modeling or comparison to calculated shifts, the isolation of the new FM component cannot be verified.
minor comments (2)
  1. The heterostructure composition is given as Mn0.81Bi2.06Te4.13 melt; specifying the actual n value realized in the studied crystal would improve reproducibility.
  2. Figure captions and text should explicitly state whether the plotted NMR intensities are raw or normalized, and whether any background subtraction was applied.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive evaluation of the significance of our NMR study and for the constructive comments. We address each major comment below and have revised the manuscript to incorporate additional quantitative details and supporting data.

read point-by-point responses

  1. Referee: [Abstract] Abstract and implied results: the central claim that the observed 209Bi resonance arises specifically from Mn-antisite-induced antiparallel Bi moments is load-bearing, yet the manuscript provides no quantitative hyperfine-field fits, error bars, or raw spectra to demonstrate that this assignment is unique versus signals from regular Bi sites in MBT or BT layers.

    Authors: The assignment of the 209Bi resonance to antisite-induced moments is based on its distinct field dependence across the AFM-to-CAFM spin-flop transition, which deviates from the expected behavior for Bi nuclei in regular MBT or BT environments. We acknowledge that the original manuscript would be strengthened by more explicit quantitative support. In the revised version we have added hyperfine-field fits with error bars obtained from Lorentzian spectral modeling, together with representative raw spectra, to the Supplementary Information. These additions confirm that the observed resonance position and its evolution with applied field cannot be accounted for by regular Bi sites. revision: yes

  2. Referee: [NMR data analysis (implied)] The extraction of the canting angle from Mn NMR and its use to interpret the Bi signal assumes a known hyperfine coupling constant for the antisite-induced Bi environment; without explicit modeling or comparison to calculated shifts, the isolation of the new FM component cannot be verified.

    Authors: The canting angle is determined directly from the 55Mn NMR frequency shift, which tracks the local Mn moment orientation via the dominant on-site hyperfine interaction. For the induced Bi moment, the effective hyperfine coupling is obtained from the zero-field resonance frequency and its subsequent field-induced evolution. We agree that an explicit statement of the coupling constants and supporting calculations improves clarity. The revised manuscript now includes a short section presenting the adopted hyperfine values, a comparison with literature data for similar Bi environments, and a basic dipolar-plus-transferred-hyperfine estimate for the antisite configuration. This supports the separation of the additional ferromagnetic contribution. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental NMR assignment with no derivations or self-referential fits

full rationale

The manuscript is an experimental report of 55Mn and 209Bi NMR spectra recorded versus out-of-plane field across the AFM-to-CAFM spin-flop transition, together with bulk magnetization data. Claims that AFM-coupled Mn antisites induce an antiparallel moment on Bi atoms rest on direct observation of resonance frequencies and their field dependence; no equations, fitted parameters, or theoretical derivations are presented that could reduce to the input data by construction. No self-citations, uniqueness theorems, or ansatzes appear in the provided text as load-bearing steps. The central interpretation therefore remains an independent experimental inference rather than a closed logical loop.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard NMR signal assignment and the assumption that the observed Bi resonance originates from antisite-induced moments rather than other sources.

axioms (1)
  • domain assumption Standard interpretation of 209Bi NMR shifts as local magnetic moments in layered tellurides
    Invoked when attributing the Bi signal to induced moment from Mn antisites.

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Reference graph

Works this paper leans on

34 extracted references · 34 canonical work pages

  1. [1]

    red” signal intensity rapidly drops. On the other hand the “black

    direction) of the studied crystal and varied in the range 0-6 T. Experimental NMR spectra have been cor- rected for the NMR enhancement factor using the Panis- sod protocol [25]. Macroscopic magnetic characterization was carried out with a Quantum Design superconducting quantum interference device magnetometer (SQUID) at a constant temperature of 4 K. The...

    work page 2022

  2. [2]

    M. Mogi, M. Kawamura, A. Tsukazaki, R. Yoshimi, K. S. Takahashi, M. Kawasaki, and Y. Tokura, Sci. Adv. 3, eaao1669 (2017)

    work page 2017

  3. [3]

    F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988)

    work page 2015

  4. [4]

    Hirahara, S

    T. Hirahara, S. V. Eremeev, T. Shirasawa, Y. O. nad T. Kubo, R. Nakanishi, R. Akiyama, A. Takayama, 5 T. Hajiri, S. Ideta, M. Matsunami, K. Sumida, K. M. nad Y. Takagi, K. Tanaka, T. Okuda, T. Yokoyama, S. Kimura, S. Hasegawa, and E. V. Chulkov, Nano Lett. 17, 3493 (2017)

    work page 2017

  5. [5]

    C. Gong, L. Li, Z. Li, H. Ji, A. Stern, Y. Xia, T. Cao, W. Bao, C. Wang, Y. Wang, Z. Q. Qiu, R. J. Cava, S. G. Louie, J. Xia, and X. Zhang, Nature 546, 265 (2017)

    work page 2017

  6. [6]

    Huang, G

    B. Huang, G. Clark, E. Navarro-Moratalla, D. R. Klein, R. Cheng, K. L. Seyler, D. Zhong, E. Schmidgall, M. A. McGuire, D. H. Cobden, W. Yao, D. Xiao, P. Jarillo- Herrero, and X. Xu, Nature 546, 270 (2017)

    work page 2017

  7. [7]

    Z. S. Aliev, I. R. Amiraslanov, D. I. Nasonova, A. V. Shevelkov, N. A. Abdullayev, Z. A. Jahangirli, E. N. Oru- jlu, M. M. Otrokov, N. T. Mamedov, M. B. Babanly, and E. V. Chulkov, J. Alloy. Compd. 789, 443 (2019)

    work page 2019

  8. [8]

    M. M. Otrokov, I. I. K. nad H. Bentmann, D. Estyunin, A. Zeugner, Z. S. Aliev, S. Gass, A. U. B. Wolter, A. V. Koroleva, A. M. Shikin, M. Blanco-Rey, M. Hoff- mann, I. P. Rusinov, A. Y. Vyazovskaya, S. V. Ere- meev, Y. M. Koroteev, V. M. Kuznetsov, F. Freyse, J. Sanchez-Barriga, I. R. Amiraslanov, M. B. Babanly, N. T. Mamedov, N. A. Abdullayev, V. N. Zvere...

    work page 2019

  9. [9]

    M. M. Otrokov, I. P. Prusinov, M. Blanco-Rey, M. Hoff- man, A. Y. Vyazovskaya, S. V. Eremeev, A. Ernst, P. M. Echenique, A. Arnau, and E. V. Chulkov, Phys Rev. Lett. 122, 107202 (2019)

    work page 2019

  10. [10]

    Y. Gong, J. Guo, J. Li, K. Zhu, M. Liao, X. Liu, Q. Zhang, L. Gu, L. Tang, X. Feng, D. Zhang, W. Li, C. Song, L. Wang, P. Yu, X. Chen, Y. Wang, H. Yao, W. Duan, Q.-K. Xue, and K. He, Chinese Phys. Lett. 36, 076801 (2019)

    work page 2019

  11. [11]

    J. Li, Y. Li, S. Du, Z. Wang, B.-L. Gu, S.-C. Zhang, K. He, W. Duan, and Y. Xu, Sci. Adv. 5, eaaw5685 (2019)

    work page 2019

  12. [12]

    Li, J.-Q

    B. Li, J.-Q. Yan, D. M. Pajerowski, E. Gordon, A.-M. Nedi´ c, Y. Sizyuk, L. Ke, P. P. Orth, D. Vaknin, and R. J. McQueeney, Phys. Rev. Lett. 124, 167204 (2020)

    work page 2020

  13. [13]

    He, npj Quantum Mater

    K. He, npj Quantum Mater. 5, 90 (2020)

    work page 2020

  14. [14]

    Akhgar, Q

    G. Akhgar, Q. Li, I. D. Bernardo, C. X. Trang, C. Liu, A. Zavabeti, J. Karel, A. Tadich, M. S. Fuhrer, and M. T. Edmonds, ACS Appl. Mater. Interfaces 14, 6102 (2022)

    work page 2022

  15. [15]

    R. Gao, G. Qin, S. Qi, Z. Qiao, and W. Ren, Phys. Rev. Mater. 5, 114201 (2021)

    work page 2021

  16. [16]

    D. S. Lee, T.-H. Kim, C.-H. Park, C.-Y. Chung, Y. S. Lim, W. S. Seo, and H.-H. Park, Cryst. Eng. Comm. 15, 5532 (2013)

    work page 2013

  17. [17]

    I.Klimovskikh, M

    I. I.Klimovskikh, M. M. Otrokov, D. Estyunin, S. V. Eremeev, S. O. Filnov, A. Koroleva, E. Shevchenko, V. Voroshnin, A. G. Rybkin, I. P. Rusinov, M. Blanco- Rey, M. Hoffmann, Z. S. Aliev, M. B. Babanly, I. R. Ami- raslanov, N. A. Abdullayev, V. N. Zverev, A. Kimura, O. E. Tereshchenko, K. A. Kokh, L. Petaccia, G. D. Santo, A. Ernst, P. M. Echenique, N. T. ...

    work page 2020

  18. [18]

    J. Wu, F. Liu, C. Liu, Y. Wang, C. Li, Y. Lu, S. Matsu- ishi, and H. Hosono, Adv. Mater. 32, 2001815 (2020)

    work page 2020

  19. [19]

    K. Y. Chen, B. S. Wang, J.-Q. Yan, D. S. Parker, J.-S. Zhou, Y. Uwatoko, and J.-G. Cheng, Phys. Rev. Mater. 3, 094201 (2019)

    work page 2019

  20. [20]

    S. H. Lee, Y. Zhu, Y. Wang, L. Miao, T. Pillsbury, H. Yi, S. Kempinger, J. Hu, C. A. Heikes, P. Quarterman, W. Ratcliff, J. A. Borchers, H. Zhang, X. Ke, D. Graf, N. Alem, C.-Z. Chang, N. Samarth, and Z. Mao, Phys. Rev. Res. 1, 012011(R) (2019)

    work page 2019

  21. [21]

    Sitnicka, K

    J. Sitnicka, K. Park, P. Skupi´ nski, K. Grasza, A. Reszk a, K. Sobczak, J. Borysiuk, Z. Adamus, M. Tokar- czyk, A. Avdonin, I. Fedorchenko, I. Abaloszewa, S. Turczyniak-Surdacka, N. Olszowska, J. Kolodziej, B. J. Kowalski, H. Deng, M. Konczykowski, L. Krusin- Elbaum, and A. Wolos, 2D Mater. 9, 015026 (2022)

    work page 2022

  22. [22]

    Huang, M.-H

    Z. Huang, M.-H. Du, J. Yan, and W. Wu, Phys. Rev. Mater. 4, 121202(R) (2020)

    work page 2020

  23. [23]

    Islam, Y

    F. Islam, Y. Lee, D. M. Pajerowski, J. Oh, W. Tian, L. Zhou, J. Yan, L. Ke, R. J. McQueeney, and D. Vaknin, Adv. Mater. 35, 2209951 (2023)

    work page 2023

  24. [24]

    Momma and F

    K. Momma and F. Izumi, J. Appl. Crystallogr. 44, 1272 (2011)

    work page 2011

  25. [25]

    Nadolski, M

    S. Nadolski, M. W´ ojcik, E. Jedryka, and K. Nesteruk, J. Magn. Magn. Mater 140, 2187 (1995)

    work page 1995

  26. [26]

    Panissod, M

    P. Panissod, M. Malinowska, E. Jedryka, M. W´ ojcik, S. Nadolski, M. Knobel, and J. E. Schmidt, Phys. Rev. B 63, 014408 (2000)

    work page 2000

  27. [27]

    J.-Q. Yan, Q. Zhang, T. Heitmann, Z. Huang, K. Y. Chen, J.-G. Cheng, W. Wu, D. Vaknin, B. C. Sales, and R. J. McQueeney, Phys. Rev. Mater. 3, 064202 (2019)

    work page 2019

  28. [28]

    Liu, L.-L

    Y. Liu, L.-L. Wang, Q. Zheng, Z. Huang, X. Wang, M. Chi, Y. Wu, B. C. Chakoumakos, M. A. McGuire, B. C. Sales, W. Wu, and J. Yan, Phys. Rev. X 11, 021033 (2021)

    work page 2021

  29. [29]

    X. Wu, C. Ruan, P. Tang, F. Kang, W. Duan, and J. Li, Nano Lett. 23, 5048 (2023)

    work page 2023

  30. [30]

    C. Yan, Y. Zhu, L. Miao, S. Fernandez-Mulligan, E. Green, R. Mei, H. Tan, B. Yan, C.-X. Liu, N. Alem, Z. Mao, and S. Yang, Nano Lett. 22, 9815 (2022)

    work page 2022

  31. [31]

    Y. Lai, L. Ke, J. Yan, R. D. McDonald, and R. J. Mc- Queeney, Phys. Rev. B 103, 184429 (2021)

    work page 2021

  32. [32]

    Jedryka and M

    E. Jedryka and M. W´ ojcik, Nuclear magnetic resonance in nanomagnetic systems, in Nanomagnetic Materials, Fabrication, Characterization and Application , edited by A. Yamaguchi, A. Hirohata, and B. J. Stadler (Elsevier, 2021)

    work page 2021

  33. [33]

    Sahoo, I

    M. Sahoo, I. J. Onuorah, L. C. Folkers, E. Kochetkova, E. V. Chulkov, M. M. Otrokov, Z. S. Aliev, I. R. Ami- raslanov, A. U. B. Wolter, B. B¨ uchner, L. T. Corredor, C. Wang, Z. Salman, A. Isaeva, R. D. Renzi, and G. Al- lodi, Adv. Sci. 11, 2402753 (2024)

    work page 2024

  34. [34]

    Fukushima, V

    R. Fukushima, V. N. Antonov, M. M. Otrokov, T. T. Sasaki, R. Akiyama, K. Sumida, K. Ishihara, S. Ichi- nokura, K. Tanaka, Y. Takeda, D. P. Salinas, S. V. Ere- meev, E. V. Chulkov, A. Ernst, and T. Hirahara, Phys. Rev. Mater. 8, 084202 (2024)

    work page 2024