  We develop a method for investigating nonequilibrium dynamics of an ultracold
system that is initially at thermal equilibrium. Our procedure is based on the
classical fields approximation with appropriately prepared initial state. As an
application of the method, we investigate the influence of thermal fluctuations
on the quantum phase transition from an antiferromagnetic to phase separated
ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We find
that at temperatures significantly lower than the critical condensation
temperature $T_c$ the scaling law for the number of created spin defects
remains intact.

Quantum Gases