Low-temperature spin freezing in the Dy₂Ti₂O₇ spin ice

We report a study of the low temperature bulk magnetic properties of the spin ice compound Dy₂Ti₂O₇ with particular attention to the (T < 4K) spin freezing transition. While this transition is superficially similar to that in a spin glass, there are important qualitative differences from spin glass behavior: the freezing temperature increases slightly with applied magnetic field, and the distribution of spin relaxation times remains extremely narrow down to the lowest temperatures. Furthermore, the characteristic spin relaxation time increases faster than exponentially down to the lowest temperatures studied. These results indicate that spin-freezing in spin ice materials represents a novel form of magnetic glassiness associated with the unusual nature of geometrical frustration in these materials.