Dirty spin ice: The effect of dilution on spin freezing in Dy₂Ti₂O₇

We have studied spin freezing in the diluted spin ice compound Dy_2-xY_xTi₂O₇ where the nonmagnetic Y ions replace the magnetic Dy ions on the frustrated pyrochlore lattice. Magnetic ac and dc susceptibility data are presented with an analysis of relaxation times for dilutions of x=0, 0.1, 0.2, and 0.4. Site dilution apparently decreases the relative number of spins participating in the icelike freezing near 16 K while leaving the freezing temperature unchanged. Correspondingly the distribution of relaxation times associated with the freezing is broadened only slightly with increasing dilution, suggesting that the freezing process observed near T=16 K involves the development of local correlations among the spins.