Spin freezing in geometrically frustrated beta-Mn probed by muon spin relaxation

Muon spin relaxation was measured down to 0.05 K on a geometrically frustra ted metallic system, beta-Mn. The observed relaxation rate increases with d ecreasing temperature and unexpectedly makes a peak at 0.5 K indicating a s pin freezing below the temperature. Actually the asymmetry is almost recove red by applying a longitudinal magnetic field of 0.1 T. But since the tail amplitude is more than half and the dynamical relaxation is still appreciab le at the lowest temperature, it is likely that the frozen moments are asso ciated with imperfection as oxygen impurity and the intrinsic ground state is fluctuating spin liquid.