Hidden order in a frustrated system: Properties of the Heisenberg Kagomé antiferromagnet

We show that the classical Heisenberg antiferromagnet on a Kagomé lattice is an example of a spin nematic. By calculating the effects of thermal fluctuations around ground states, and by Monte Carlo simulations, we find entropically driven, local spin-nematic order at low temperature T with a correlation length which is divergent in the limit T→0. Dynamical correlations are also studied, within the harmonic approximation, in the nematically ordered states.