Frequency dependence of Tf and short time remanence for Eu0.4Sr0.6S spin glass

Abstract

We report on the frequency variation of the freezing temperature and on the time variation of the magnetization of the insulating spin‐glass Eu_0.4Sr_0.6S. Faraday rotation was used to monitor optically the susceptibility or the magnetization and is well adapted to measurements in a large frequency range (10⁻²–10⁷ Hz) or at various time scale (down to 25 ns). The temperature T_f(ν) associated with the maximum of the susceptibility peak exhibits a linear dependence with Log(ν) in the range 10²–10⁷ Hz. At lower frequencies (down to 10⁻² Hz) it approaches a ’’static’’ limit equal to 1.55 K. This result cannot be explained by a model of superparamagnetic clouds. The frequency shift of the freezing temperature is experimentally shown to be related to the occurrence of a remanent magnetization during the time associated with the measuring frequency. Finally the time dependent behavior of the magnetization was investigated down to 25 ns after cutting a weak magnetic field (∼2 Oe). The main part of the magnetization is shown to relax more quickly than 25 ns even at 1.26 K. The only change when lowering the temperature below T_f is the emergence of the remanent magnetization; its time dependence is briefly discussed.