Dy2Ti2O7 spin ice: a test case for emergent clusters in a frustrated magnet.

Dy2Ti2O7 is a geometrically frustrated magnetic material with a strongly correlated spin ice regime that extends from 1 K down to as low as 60 mK. The diffuse elastic neutron scattering intensities in the spin ice regime can be remarkably well described by a phenomenological model of weakly interacting hexagonal spin clusters, as invoked in other geometrically frustrated magnets. We present a highly refined microscopic theory of Dy2Ti2O7 that includes long-range dipolar and exchange interactions to third nearest neighbors and which demonstrates that the clusters are purely fictitious in this material.

Spin Hamiltonian, competing small energy scales, and incommensurate long-range order in the highly frustrated Gd(3)Ga(5)O(12) garnet antiferromagnet.

Despite the availability of a spin Hamiltonian for the Gd(3)Ga(5)O(12) garnet (GGG) for over 25 years, there has so far been little theoretical insight regarding the many unusual low temperature properties of GGG. Here we investigate GGG in zero magnetic field using mean-field theory. We reproduce the spin liquid-like correlations and, most importantly, explain the positions of the sharp peaks seen in powder neutron diffraction experiments.