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Magnetocaloric study of spin relaxation in dipolar spin ice Dy2Ti2O7

M. Orendáč, J. Hanko, E. Čižmár, A. Orendáčová, M. Shirai, and S. T. Bramwell
Phys. Rev. B 75, 104425 – Published 27 March 2007
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  • INTRODUCTION
  • EXPERIMENT
  • RESULTS
  • DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    The magnetocaloric effect of polycrystalline samples of pure and Y-doped dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3to6K and in magnetic fields of up to 2T. As well as being of intrinsic interest, it is proposed that the magnetocaloric effect may be used as an appropriate tool for the qualitative study of slow relaxation processes in the spin ice regime. In the high-temperature regime the temperature change on adiabatic demagnetization was found to be consistent with previously published entropy vs temperature curves. At low temperatures (T<0.4K) cooling by adiabatic demagnetization was followed by an irreversible rise in temperature that persisted after the removal of the applied field. The relaxation time derived from this temperature rise was found to increase rapidly down to 0.3K. The data near 0.3K indicated a transition into a metastable state with much slower relaxation, supporting recent neutron-scattering results. In addition, magnetic dilution of 50% concentration was found to significantly prolong the dynamical response in the mK temperature range, in contrast with results reported for higher temperatures at which the spin correlations are suppressed. These observations are discussed in terms of defects and loop correlations in the spin ice state.

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    • Received 21 September 2006

    DOI:https://doi.org/10.1103/PhysRevB.75.104425

    ©2007 American Physical Society

    Authors & Affiliations

    M. Orendáč*, J. Hanko, E. Čižmár, and A. Orendáčová

    • Centre of Low Temperature Physics, Faculty of Science, P. J. Šafárik University and Institute of Experimental Physics SAS, Park Angelinum 9, 041 54 Košice, Slovakia

    M. Shirai

    • Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom

    S. T. Bramwell

    • Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom and London Centre for Nanotechnology, 17–19 Gordon Street, London WC1H OAH, United Kingdom

    • *Electronic address: orendac@kosice.upjs.sk

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    Vol. 75, Iss. 10 — 1 March 2007

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    Images

    • Figure 1
      Figure 1
      Temperature dependence of the entropy of powdered Dy2Ti2O7. Open symbols denote entropy calculated from magnetic specific heat (Ref. 3) in various magnetic fields (squares B=0T, circles B=0.5T, triangles up B=1T, stars B=1.25T, triangles down B=1.5T, hexagons B=2T). Full circles represent data obtained from adiabatic demagnetization. The full line denotes the entropy estimated from lattice specific heat.Reuse & Permissions
    • Figure 2
      Figure 2
      Temperature dependence of entropy of Dy2Ti2O7 below T=2K in B=0 (dashed line) and B=0.5T (solid line). Numbered full circles denote an initial state (1), an intermediate state (2) reached by adiabatic magnetization, state (3) reached by cooling in constant field, and state (4) obtained after adiabatic demagnetization. See text for a more detailed discussion.Reuse & Permissions
    • Figure 3
      Figure 3
      Time dependences of temperature during adiabatic demagnetization of Dy2Ti2O7 for selected sweep rates. Full circles: 7.8mT∕min; empty squares: 15.6mT∕min; full triangles: 23.5mT∕min; empty hexagons: 47.1mT∕min; full stars: 110mT∕min. Inset: More detailed view of the time development of temperature at the end of the demagnetization for the sweep rate 23.5mT∕min. Solid line represents the least-squares fit using Eq. (2). The moment when magnetic field reaches zero value is denoted by arrow.Reuse & Permissions
    • Figure 4
      Figure 4
      Time dependences of temperature during adiabatic demagnetization of (DyY)Ti2O7 for selected sweep rates. The arrow denotes the moment when magnetic field reaches zero value.Reuse & Permissions
    • Figure 5
      Figure 5
      Magnetic-field dependences of temperature during adiabatic demagnetization of (a) Dy2Ti2O7 and (b) (DyY)Ti2O7 for corresponding sweep rates denoted in Figs. 3, 4, respectively. The data of temperature are presented only to the point at which the magnetic field reaches zero value. See text for a more detailed discussion.Reuse & Permissions
    • Figure 6
      Figure 6
      Dependence of Tfinal, the resulting temperature after the demagnetization (empty circles) and T0, the temperature at which magnetic field reached zero value (full squares), for Dy2Ti2O7 on the used sweep rate. Three lowest temperatures were reached using 1.5, 2.2, and 3.1mT∕min, respectively. The solid lines are guides for the eye.Reuse & Permissions
    • Figure 7
      Figure 7
      Dependence of the estimated relaxation time of Dy2Ti2O7 (empty circles) on the used sweep rate.Reuse & Permissions
    • Figure 8
      Figure 8
      Temperature dependence of the relaxation time of Dy2Ti2O7 (empty circles). The solid line and dashed lines represent least-squares fits from 0.3to0.4K using relations τ=a∙T−9 with a=7.22e−3K9s and τ=b*exp(Δ∕kT) with b=2.5e–3s and Δ∕k=3.6K, respectively. Inset: Comparison of the relaxation time obtained from the present work (empty circles) and from Ref. 37 (full squares).Reuse & Permissions
    • Figure 9
      Figure 9
      Time dependence of the temperature of the thermometer during the study of the thermal relaxation between the thermometer and powdered Dy2Ti2O7 (empty circles). The solid lines represent least-square fits after finishing overheating of the thermometer. See text for a more detailed discussion.Reuse & Permissions
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