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Criticality in a disordered quantum antiferromagnet studied by neutron diffraction

E. Wulf, D. Hüvonen, J.-W. Kim, A. Paduan-Filho, E. Ressouche, S. Gvasaliya, V. Zapf, and A. Zheludev
Phys. Rev. B 88, 174418 – Published 20 November 2013
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  • INTRODUCTION
  • MATERIALS AND EXPERIMENTAL…
  • RESULTS AND DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    Field-induced magnetic ordering in the structurally disordered quantum magnets Ni(Cl1−xBrx)2·4SC(NH2)2, x=8% and 13%, is studied by means of neutron diffraction. The order-parameter critical exponent is found to be very close to its value β=0.5 expected for magnetic Bose-Einstein condensation in the absence of disorder. This result applies to temperatures down to 40 mK, and a 1 T range in magnetic field. The crossover exponent is found to be ϕ∼0.4 for temperature ranges as small as 300 mK. Possible reasons for a discrepancy with recent numerical simulations and bulk measurements are discussed.

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    • Received 3 October 2013

    DOI:https://doi.org/10.1103/PhysRevB.88.174418

    ©2013 American Physical Society

    Authors & Affiliations

    E. Wulf1, D. Hüvonen1, J.-W. Kim2,3, A. Paduan-Filho4, E. Ressouche5, S. Gvasaliya1, V. Zapf2, and A. Zheludev1,*

    • 1Neutron Scattering and Magnetism, Laboratory for Solid State Physics, ETH Zürich, Zürich, Switzerland
    • 2National High Magnetic Field Laboratory, MPA-CMMS Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
    • 3Lujan Center for Neutron Scattering, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
    • 4High Magnetic Field Laboratory, University of São Paulo, 05315-970 São Paulo, Brazil
    • 5INAC/SPSMS-MDN, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France

    • *zhelud@ethz.ch; http://www.neutron.ethz.ch/

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    Issue

    Vol. 88, Iss. 17 — 1 November 2013

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    • Figure 1
      Figure 1
      Neutron intensity measured in the x=8% Ni(Cl1−xBrx)2·4SC(NH2)2 sample at the (0.5,0.5,0.5) Bragg position, vs temperature and magnetic field applied along the c axis.Reuse & Permissions
    • Figure 2
      Figure 2
      (a)–(c) Symbols: typical constant-temperature field scans of the magnetic Bragg peak intensity in x=8% (a) and x=13% (b), (c) Ni(Cl1−xBrx)2·4SC(NH2)2 samples. Solid lines are power-law fits, as described in the text. (d),(e) Fitted order-parameter critical exponent β (d) and critical field Hc (e) for the data in graphs (b) and (c), plotted as functions of maximum field Hmax used in the fitting process. The highlighted symbols illustrate the choice of the narrowest useful fitting range, as described in the text.Reuse & Permissions
    • Figure 3
      Figure 3
      Data analysis for the x=8% Ni(Cl1−xBrx)2·4SC(NH2)2 sample. (a) Symbols: temperature dependence of the order-parameter exponent β obtained in fits to individual fit scans in the range 0<H<Hc+ΔH, ΔH=1.0 T. The line represents an average obtained for all data measured at T≲0.3 K. (b) Symbols: temperature dependence of the critical field Hc obtained in fits to individual fit scans in the range 0<H<Hc+ΔH, ΔH=1.0 T. The line is a power-law fit in the range 0<T<Tmax, Tmax=0.85 K, as described in the text. (c) Fitted value of the critical index ϕ as a function of fitting interval. The solid symbol represents the narrowest useful fitting range, as described in the text.Reuse & Permissions
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