Spin dynamics in granular CoxCu1-x by μSR

CoxCu1-x samples with x=0.01,0.02,0.05 produced by melt spinning were probed with zero-field and longitudinal field μSR. For x=0.05, freezing into a spin glass state below 15 K is seen. Spectra between 15 and ∼150 K consist of the sum of two relaxation functions: a weakly dynamic Lorentzian Kubo-Toyabe (DLKT) and a root exponential (REX) relaxation. The cause is either a size distribution of precipitates or a strong heterogeneity in the spatial cluster arrangement. Above ∼150 K, relaxation is purely REX with the slow rate of 1.5 μs-1, nearly independent of temperature. Persistent correlations between the clusters slow down the fluctuations of cluster moments and the state of free cluster moments is not reached in the temperature range investigated. The μSR response of the samples with lower Co concentration (0.2 and 0.1 at%) is characterized mainly by an increase of spin dynamics and a smaller mean field, implying a reduction of cluster-cluster couplings and a reduction of the moment of the precipitates. For x=0.1, a spin glass state is not formed down to 2 K