Effect of exchange-bond randomization in a highly two-dimensional quantum Heisenberg antiferromagnet

ORAL

Abstract

We present an investigation of the effect of randomizing exchange coupling strengths in the S = 1/2 square lattice quasi-two-dimensional quantum Heisenberg antiferromagnet (QHAF) (QuinH)2Cu(ClxBr1−x)4●2H2O (QuinH = Quinolinium, C9H8N+), with 0 ≤ x ≤ 1. Pulsed-field magnetization allows us to estimate an effective in-plane exchange strength in a regime where exchange fosters short-range order, while the temperature at which long-range order occurs (TN) is found using muon-spin relaxation, allowing us to construct a phase diagram for the series. We evaluate the effectiveness of disorder in suppressing the TN and the ordered moment size and find an extended disordered phase in the region 0.4 ≤ x ≤ 0.8 where no magnetic order occurs. The observed critical substitution levels are accounted for by an energetics-based competition between different local magnetic orders. We demonstrate experimentally that the ground-state disorder is driven by quantum effects of the exchange randomness, a feature that has been predicted theoretically and has implications for other disordered quasi-two-dimensional QHAFs.

*Work at the University of Warwick is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 681260).

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Presenters

  • Paul Goddard

    • Department of Physics, University of Warwick
    • University of Warwick
    • Physics, University of Warwick

Authors

  • Paul Goddard

    • Department of Physics, University of Warwick
    • University of Warwick
    • Physics, University of Warwick

  • Fan Xiao

    • Laboratory for Neutron Scattering, Paul Scherrer Institut

  • William Blackmore

    • Department of Chemistry, University of Manchester
    • Manchester University

  • Benjamin Michael Huddart

    • Department of Physics, Durham University
    • Department of Physics, University of Durham

  • Matjaz Gomišek

    • Jozef Stefan Institute

  • Thomas J Hicken

    • Department of Physics, Durham University

  • Chris Baines

    • Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut
    • Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute
    • Paul Scherrer Institut

  • Peter J Baker

    • ISIS Pulsed Neutron and Muon Facility, STFC Rutherford Appleton Laboratory
    • ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX110QX, United Kingdom
    • ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, UK

  • Francis L Pratt

    • ISIS Pulsed Neutron and Muon Facility, STFC Rutherford Appleton Laboratory

  • Stephen Blundell

    • Department of Physics, University of Oxford
    • University of Oxford
    • Physics, University of Oxford
    • Univ of Oxford

  • Helen Lu

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • National High Magnetic Field Laboratory (NHMFL), Los Alamos

  • John Singleton

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • Los Alamos National Lab
    • Los Alamos National Laboratory
    • LANL, NHMFL
    • National High Magnetic Field Laboratory (NHMFL), Los Alamos

  • Dariusz Gawryluk

    • Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut
    • Laboratory for Multiscale Materials Experiments, Paul Scherrer Institute

  • Mark Turnbull

    • Carlson School of Chemistry and Biochemistry and Department of Physics, Clark University
    • Clark University

  • Karl W Krämer

    • Department of Chemistry and Biochemistry, University of Bern

  • Tom Lancaster

    • Department of Physics, Durham University
    • Department of Physics, University of Durham