Field-Induced Transitions in a Kagomé Antiferromagnet

The thermal order by disorder effect in magnetic field is studied for a classical Heisenberg antiferromagnet on the Kagomé lattice. Using analytical arguments we predict a unique $H$- $T$ phase diagram for this strongly frustrated magnet: states with a coplanar and a uniaxial triatic order parameter, respectively, at low and high magnetic fields and an incompressible collinear spin-liquid state at one-third of the saturation field. We also present the Monte Carlo data which confirm the existence of these phases.