  The spin dynamics of geometrically frustrated pyrochlore antiferromagnets
Y2Mo2O7 and Tb2Mo2O7 have been investigated using muon spin relaxation. A
dramatic slowing down of the moment fluctuations occurs as one approaches the
spin freezing temperatures (TF=22 K and 25 K respectively) from above. Below TF
there is a disordered magnetic state similar to that found in a spin glass but
with a residual muon spin relaxation rate at low temperatures. These results
show that there is a large density of states for magnetic excitations in these
systems near zero energy.
