  Using muon-spin-relaxation measurements we show that the pyrochlore compound
Gd2Ti2O7, in its magnetically orderered phase below ~ 1 K, displays persistent
spin dynamics down to temperatures as low as 20 mK. The characteristics of the
induced muon relaxation can be accounted for by a scattering process involving
two magnetic excitations, with a density of states characterized by an upturn
at low energy and a small gap depending linearly on the temperature. We propose
that such a density of states is a generic feature of geometrically frustrated
magnetic materials.
