Time and field dependence of the magnetization in AuFe, AgMn, and ThGd spin glasses

We report time dependence measurements of the zero field cooled magnetization (MZFC) and the thermoremanent magnetization (TRM) for AuFe (2 and 4 at.%), AgMn (1 and 4 at.%), and Th1−xGdx (3⩽x⩽20 at.%) as a function of the magnetic field. The time effect behavior was similar in the three systems. The time dependence can be fitted with a log (t) law when the temperature T is not too close to the reversible temperature TR at which the magnetization becomes reversible. The rate of the TRM decay increased with H, presented a maximum with T, and extrapolated to zero when T→TR.