A Mossbauer spectroscopic investigation of the dynamics of magnetic correlations in the spin glasses Au(Fe) and Y(Fe,Al)2 above Tf

Transmission 57Fe Mossbauer spectra of the typical spin glasses Y(FexAl1-x)2 (x=0.75,0.65,0.40,0.25) and Au1-xFex (x=0.15,0.05) were taken from 4.2 K up to room temperature in applied fields (Ba) up to 15 T. To account for the correlations which appear at temperatures T 7 times the freezing temperature (Tf) a model is employed according to which magnetic correlations are formed and decay in the course of time. The resulting field values fit to those at higher temperatures and to the zero-field spectra at 4.2 K. The mean relaxation times depend linearly on Ba1/2/T3/2 and scale with Tf. The mean lifetime of the correlations scales with T/Tf and increases with increasing Ba and decreasing temperature, whereas the mean time during which the Fe atoms are uncorrelated is only mildly dependent on Ba, which indicates that the applied field does not favour the formation of correlations but that it stabilizes the correlations if their magnetic moment is oriented parallel to Ba. Three to five Fe atoms are included in the correlated regions.