  We present single-crystal neutron-diffuse-scattering measurements with
polarization analysis on the spin ice Ho2-xYxTi2O7 (x = 0, 0.3, and 1). At 2 K,
the spin flip scattering patterns are typical of a nearest-neighbor spin ice
and the effects of Y doping are seen in the width of the pinch points. At
low-T, the spin flip patterns are characteristic of a dipolar spin ice and are
unaffected by Y doping. In the non-spin flip channel, we observe the signature
of strong antiferromagnetic correlations at the same T as the dipolar spin ice
correlations appear in the spin flip channel. These experimental observations
have been well reproduced by our Monte Carlo simulations.
