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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.

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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