Finite-temperature transition of the distorted kagome-lattice Heisenberg   antiferromagnet
  Motivated by the recent experiment on kagome-lattice antiferromagnets, we study the zero-field ordering behavior of the antiferromagnetic classical Heisenberg model on a uniaxially distorted kagome lattice by Monte Carlo simulations. A first-order transition, which has no counterpart in the corresponding undistorted model, takes place at a very low temperature. Origin of the transition is ascribed to a cooperative proliferation of topological excitations inherent to the model. 
Hiroshi Masuda, Tsuyoshi Okubo and Hikaru Kawamura
cond-mat.stat-mech