Dispersive excitations in the $S=1$ antiferromagnet Ba$_3$Mn$_2$O$_8$

ORAL

Abstract

We present powder inelastic neutron scattering measurements on the $S=1$ dimerized antiferromagnet Ba$_3$Mn$_2$O$_8$. The measured $T=1.4$~K magnetic spectrum exhibits a spin-gap of $\Delta = 0.99$~meV and a dispersive spectrum with a bandwidth of approximately $1.67$~meV. Comparison to a coupled dimer model of the dispersion and scattering intensity yields an accurate description of the exchange constants in Ba$_3$Mn$_2 $O$_8$. Interdimer exchange between the stacked triangular lattice dimer bilayers is found to be two orders of magnitude weaker than the intradimer exchange resulting in a quasi-two- dimensional frustrated bilayer triangular lattice. The wave- vector dependent scattering intensity also confirms the proposed $S=1$ dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet- triplet and thermally activated triplet-quintet excitations, with temperature dependent damping and spin-gap consistent with current models for weakly coupled quantum spin-liquids.

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Authors

  • Matthew Stone

    • Oak Ridge National Laboratory
    • Neutron Scattering Science Division, Oak Ridge National Laboratory

  • Mark Lumsden

    • Oak Ridge National Laboratory, Oak Ridge, TN 37831
    • Oak Ridge National Laboratory, Oak Ridge TN 37831
    • Neutron Scattering Science Division, Oak Ridge National Laboratory

  • Eric Samulon

    • Department of Applied Physics and Geballe Laboratory, Stanford University

  • Yiming Qiu

    • National Institute of Standards and Technology (NCNR), U. Maryland (Materials Science and Engineering)
    • Department of Materials Science and Engineering, University of Maryland

  • Cristian Batista

    • Theoretical Division, Los Alamos National Laboratory

  • Ian Fisher

    • Department of Applied Physics and Geballe Laboratory
    • Stanford University