Magnetic Correlations in Spin Glasses above the Freezing Temperature investigated by High Field Mössbauer Spectroscopy

Abstract

The strong dynamics of magnetic correlations are observed by high field ⁵⁷Fe Mössbauer 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 10T_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 &tgr;_off and their decay after a time &tgr;_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 &tgr;_on and &tgr;_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 ¿ _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.