Specific Heat of Kagomé Ice in the Pyrochlore Oxide Dy₂Ti₂O₇

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A novel macroscopically degenerate state called kagomé ice, which was recently found in a spin ice compound Dy₂Ti₂O₇ in a magnetic field applied along the [111] direction of the cubic unit cell, is studied by specific heat measurements. The residual entropy of the kagomé ice is estimated to be 0.65 J/K mol Dy, which is nearly 40% of that for the tetrahedral spin ice obtained in a zero field (1.68 J/K mol Dy) and is in good agreement with a theoretical prediction. It is also reported that the kagomé ice state, which is stabilized at a range of magnetic field of 0.3–0.6 T, is a “gas” phase and condenses into a “liquid” phase with nearly zero entropy at a critical field of 1 T.