Pauling entropy, metastability and equilibrium in Dy${}_2$Ti${}_2$O${}_7$ spin ice

Abstract

Determining the fate of the Pauling entropy in the classical spin ice material Dy${}_2$Ti${}_2$O${}_7$ with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice - the dipolar spin ice model - predicts an ordering transition at $T\approx 0.15$ K, but recent experiments by Pomaranski $etal.$ suggest an entropy recovery over long time scales at temperatures as high as $0.5$ K, much too high to be compatible with theory. Using neutron scattering and specific heat measurements at low temperatures and with long time scales ($0.35$ K$/10^6$ s and $0.5$ K$/10^5$ s respectively) on several isotopically enriched samples we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Further, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez $etal.$ are, after all, essentially correct: the short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.

arXiv comment9 pages, 7 figures

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• Structural magnetic glassiness in spin ice Dy${}_2$Ti${}_2$O${}_7$
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• The magnetic behaviour of Dy${}_2$Ir${}_2$O${}_7$ -- beyond the mean field approximation
• Magnetic Monopoles and Dark Matter
• Screening and the Pinch Point Paradox in Spin Ice
• Extremely slow non-equilibrium monopole dynamics in classical spin ice
• Spin ice in a general applied magnetic field: Kasteleyn transition, magnetic torque and rotational magnetocaloric effect
• Tunable critical correlations in kagome ice
• Traversing the pyrochlore stability diagram; microwave-assisted synthesis and discovery of mixed B-site Ln${}_2$InSbO${}_7$ family
• Tuning interactions in the spin-ice materials Dy${}_2$Ge${}_{2-x}$Si${}_x$O${}_7$ by silicon substitution
• Room temperature spin-ice physics in cadmium cyanide
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• Universal dynamics of magnetic monopoles in two-dimensional kagomé ice
• Low-temperature high-frequency dynamic magnetic susceptibility of classical spin-ice Dy${}_2$Ti${}_2$O${}_7$
• Magnetic monopole relaxation effects in spin ice Dy${}_2$Ti${}_2$O${}_7$
• Ferromagnetic fragmented state in the pyrochlore Ho${}_2$Ru${}_2$O${}_7$
• Dynamic scaling theory for a field quench near the Kasteleyn transition in spin ice