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Abstract:
Around 0.5 K, the entropy of the spin ice Dy2Ti2O7 has a plateaulike
feature close to Pauling's residual entropy derived originally for water
ice, but an unambiguous quantification towards lower temperature is
prevented by ultraslow thermal equilibration. Based on the specific-heat
data of (Dy1-xYx)(2)Ti2O7 we analyze the influence of nonmagnetic
dilution on the low-temperature entropy. With increasing x, the
ultraslow thermal equilibration rapidly vanishes, the low-temperature
entropy systematically decreases, and its temperature dependence
strongly increases. These data suggest that a nondegenerate ground state
is realized in (Dy1-xYx)(2)Ti2O7 for intermediate dilution. This
contradicts the expected zero-temperature residual entropy obtained from
a generalization of Pauling's theory for dilute spin ice, but is
supported by Monte Carlo simulations.
