Experimental evidence for spatial inhomogeneous spin freezing inCuMn

Although the time correlation function of the impurity spins in spin glasses around the ordering temperature $T_f$ has been well determined by various experiments, microscopic insight into the development of spatial correlations during freezing is still lacking. In order to obtain direct information on this aspect we undertook a high-precision study of the muon-spin-relaxation function for the CuMn system just above $T_f$ by means of the zero-field muon-spin-relaxation (μSR) technique. The data were analyzed on the basis of either a spatially homogeneous or inhomogeneous spin-freezing model. While the former failed to fit the data the latter provided an excellent description. This is a strong indication for the coexistence of regions of fast spin fluctuations with regions of more strongly correlated spins at about 1.5$T_f$. The zero-field μSR technique is shown to be advantageous as a method for investigating spatial inhomogeneity in detail.