Competing Interactions in the Antiferromagnetic State of the Axion Insulator Candidate MnBi<sub>2</sub>Te<sub>4</sub>

ORAL

Abstract

A new class of materials, antiferromagnetic topological insulators, has been predicted to realize the bulk axion insulator with a large and in some cases quantized magneto-electric coefficient. Hexagonal MnBi2Te4 is a candidate material and here we report neutron scattering experiments conducted at the NIST Center for Neutron Research to understand its magnetism. We confirm A-type antiferromagnetic order (alternating FM basal planes with spins along the hexagonal axis) with TN=24 K. Inelastic scattering reveals an excitation spectrum with a bandwidth of 4.5 meV and gap △<0.6 meV. Modelling these data using spin-wave theory, we obtain an effective spin Hamiltonian for MnBi2Te4 that features competing ferro- and antiferromagnetic interactions within the basal plane.

*This work was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0019331.

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Presenters

  • Vincent Morano

    • Johns Hopkins University

Authors

  • Vincent Morano

    • Johns Hopkins University

  • Veronica Stewart

    • Johns Hopkins University

  • Yiming Qiu

    • Center for Neutron Research, National Institute of Standards and Technology
    • National Institute of Standards and Technology
    • NIST
    • NIST Center for Neutron Research, National Institute of Standards and Technology

  • Craig Brown

    • Center of Neutron Research, National Institute of Standards and Technology
    • NIST Center for Neutron Research
    • NIST Center for Neutron Research, NIST
    • Center for Neutron Research, National Institute of Standards and Technology
    • National Institute of Standards and Technology
    • NCNR, NIST

  • Tyrel McQueen

    • Johns Hopkins University
    • Chemistry, Johns Hopkins Univ
    • Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University

  • Collin Leslie Broholm

    • The Johns Hopkins University
    • Johns Hopkins University
    • Physics and Astronomy, Johns Hopkins University
    • Physics, The Johns Hopkins University
    • Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University