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

Muon spin relaxation was measured down to 0.05 K on a geometrically frustrated metallic system, β-Mn. The observed relaxation rate increases with decreasing temperature and unexpectedly makes a peak at 0.5 K indicating a spin freezing below the temperature. Actually the asymmetry is almost recovered 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 appreciable at the lowest temperature, it is likely that the frozen moments are associated with imperfection as oxygen impurity and the intrinsic ground state is fluctuating spin liquid.