Spin ordering and partial ordering in holmium titanate and related systems- art. no. 184412

We take another look at two compounds which have been discussed as possible realizations of "spin ice," namely holmium titanate and dysprosium titanat e. As we have earlier observed, holmium titanate does not display icelike b ehavior at low temperatures because the long-ranged dipolar interactions be tween spins are strong compared to the nearest-neighbor interactions. We sh ow, exactly, that the true around state of this system must be fully ordere d, but simulations only reach partially ordered states because there are in finite energy barriers separating these from the true ground state. We also show that the true ground state of our model of dysprosium titanate is als o fully ordered, and offer some explanations as to why simulations and expe riments show icelike behavior. We discuss the effect on these systems of an applied magnetic field. Finally, we discuss several other models which sho w similar partial or full ordering in their ground states, including the we ll-known Ising model on the fee lattice.