  By considering the constrained motion of classical spins in a geometrically
frustrated magnet, we find a dynamical freezing temperature below which the
system gets trapped in metastable states with a "frozen" moment and dynamical
heterogeneities. The residual collective degrees of freedom are strongly
correlated, and by spontaneously forming aggregates, they are unable to
reorganize the system. The phase space is then fragmented in a macroscopic
number of disconnected sectors (broken ergodicity), resulting in self-induced
disorder and "thermodynamic" anomalies, measured by the loss of a finite
configurational entropy. We discuss these results in the view of experimental
results on the kagome compounds, SrCr(9p)Ga(12-9p)O19, (H30)Fe3(SO4)2(OH)6,
Cu3V2O7(OH)2.2H2O and Cu3BaV2O8(OH)2.
