On the frequency dependence of the transition temperature in spin glasses

Abstract

For the first time, the frequency dependence of T f (temperature of the maximum of the a.c. susceptibility of spin-glasses) is shown to obey a Fulcher law τ = τ o exp [ E a / k( T f − T o )]. This observed as well in the case of dilute alloys (or R.K.K.Y. spin-glasses : Cu Mn, Au Fe, …) as for frustrated systems (Eu 1-xGd xS, Eu xSr 1-xS …). For R.K.K.Y. spin- glasses, only in the case of a very small amplitude, V o of the R.K.K.Y. interaction, this time dependence approaches an Arrhenius law. In the case of “frustrated” spin-glasses the concentration is the main parameter to determine the kind of frequency dependence of T f. These properties are evidence for a glass-like phase transition in spin-glasses. The scaling of the frequency dependence of T f with V o is justified for R.K.K.Y. spin-glasses from present data.