  We investigate two-dimensional frustrated Heisenberg magnets using
non-perturbative renormalization group techniques. These magnets allow for
point-like topological defects which are believed to unbind and drive either a
crossover or a phase transition which separates a low temperature, spin-wave
dominated regime from a high temperature regime where defects are abundant. Our
approach can account for the crossover qualitatively and both the temperature
dependence of the correlation length as well as a broad but well defined peak
in the specific heat are reproduced. We find no signatures of a finite
temperature transition and an accompanying diverging length scale. Our analysis
is consistent with a rapid crossover driven by topological defects.
