We report the specific heat and entropy of single crystals of the spin icecompound Dy2Ti2O7 at temperatures down to 0.35 K. We apply magnetic fieldsalong the four characteristic directions: [100], [110], [111] and [112].Because of Ising anisotropy, we observe anisotropic release of the residualzero-point entropy, attributable to the difference in frustrationdimensionality. In the high magnetic field along these four directions, theresidual entropy is almost fully released and the activation entropy reachesRln2. However, in the intermediate field region, the entropy in fields alongthe [111] direction is different from those for the other three fielddirections. For the [111] direction the frustration structure changes from thatof three-dimensional(3D) pyrochlore to that of two-dimensional(2D) Kagome-likelattice with constraint due to the ice rule, leading to different values ofzero-point entropy.
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