Finite-temperature properties of frustrated classical spins coupled to the lattice

We present extensive Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest (J(1)) and next-nearest (J(2)) exchange couplings on the square lattice coupled to the lattice degrees of freedom. The Ising-like phase transition, which appears for J(2)/J(1)>1/2 in the pure spin model, is strengthened by the spin-lattice coupling and is accompanied by a lattice deformation from a tetragonal symmetry to an orthorhombic one. Evidence that the universality class of the transition does not change with the inclusion of the spin-lattice coupling is reported. Implications for Li2VOSiO4, the prototype for a layered J(1)-J(2) model in the collinear regime, are also discussed.