Triangular and Kagome Antiferromagnets with a Strong Easy-Axis Anisotropy

We consider S > 3/2 kagome and triangular lattice magnets with strong easy-axis single-ion anisotropy D and antiferromagnetic exchange J. When D > J, the low energy states selected by the anisotropy map onto configurations of the corresponding classical Ising antiferromagnet. Subleading O(J(3)S/D(2)) multispin interaction arising from the transverse quantum dynamics makes the low-temperature behavior very different from the well-known classical case: The kagome magnet goes into a semiclassical spin-liquid state with distinctive and unusual short-range correlations below a crossover temperature T(*)approximate to 0.08J(3)S/D(2), while the triangular magnet undergoes a first-order transition at T(c)approximate to 0.1J(3)S/D(2) to an orientationally ordered collinear state that gives rise to a novel zero-magnetization plateau for small magnetic fields along the easy axis. Possible experimental implications are also discussed.