The Magnetocaloric Effect in Exotic Spin Chain Compounds

ORAL

Abstract

The seminal S=1/2 chain model is highly sensitive to deviations from the ideal Hamiltonian which, together with the intrinsic quantum fluctuations due to low-dimensionality, can induce a range of exotic behaviours. One such perturbation is an alternating local crystal structure, which produces a field-induced gap to solitonic excitations and promotes non-collinear spin structures. The sine-Gordon (SG) model captures this behaviour at low fields, but breaks down as systems approach saturation. We report the results of pulsed-field adiabatic measurements of the magnetocaloric effect in the archetypal SG chain material [(pym)-Cu(NO3)2(H2O)2], plus the novel chiral spin-chain compound with four-fold periodicity along the chain axis: [Cu(pym)(H2O)4]SiF6.H2O, (pym=N2C4H4). The chiral system displays a rich variety of excitations above a gap which, in contrast to the SG model, has a linear field-dependence and suppressed magnitude. These measurements provide a powerful means of probing both the magnetic entropy across phase diagrams, and the quantum critical behaviour near saturation. Our results highlight similar underlying physics in the compounds, but also indicate intriguing qualitative differences in the quantum phase transitions at high field.

*We thank the ERC and ISSP for funding

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Presenters

  • Robert Williams

    • Physics, University of Warwick

Authors

  • Robert Williams

    • Physics, University of Warwick

  • Paul Goddard

    • Physics, University of Warwick
    • Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
    • Warwick University
    • Department of Physics, University of Warwick

  • Sam Curley

    • Physics, University of Warwick
    • Warwick University

  • Yoshimitsu Kohama

    • ISSP, Tokyo University
    • The Institute for Solid State Physics, University of Tokyo
    • Institute for Solid State Physics, University of Tokyo
    • The Institute for Solid State Physics, The University of Tokyo

  • Akira Matsuo

    • The Institute for Solid State Physics, University of Tokyo
    • University of Tokyo

  • Sydney Kaech

    • Chemistry, Eastern Washington University

  • Zachary Manson

    • Chemistry, Eastern Washington University
    • Department of Chemistry and Biochemistry, Eastern Washington University

  • Jamie Manson

    • Chemistry, Eastern Washington University
    • Dept. of Chemistry and Biochemistry, Eastern Washington University
    • Eastern Washington University
    • Department of Chemistry and Biochemistry, Eastern Washington University