Magnetic correlations in spin glasses above the freezing temperature investigated by high field Mossbauer spectroscopy

The strong dynamics of magnetic correlations are observed by high field Fe-57 MGssbauer investigations for the spin glasses AuFe and Y(Fe, Al)(2) in the temperature interval between the freezing temperature T-f and approximately 7 to 10 T-f. All recorded spectra can be analysed with a model which takes into account these dynamics by allowing the formation of correlated states after a stochastically varying time tau(off) and their decay after a time tau(on), restricting the number of subspectra to the different number of Fe atoms in the first neighbour shell. Whereas for the different Fe environments, in addition to centre shift and quadrupole splitting, different hyperfine fields of the two stochastically formed states can always be resolved, the same set of tau(on) and tau(off) values was obtained for all subspectra above approximately 4T(f). The external field hinders the decay of the correlated regions. The temperature dependence of tau(on) scales with T-f and exhibits a power law with exponents of -2 for the Fe-rich and -1 for the Fe-poor compounds.