Off-equilibrium fluctuation-dissipation relation in a spin glass

We report new experimental results obtained onthe insulating spin glass CdCrInS_4. Our experimental setup allows a quantitative comparison between thethermo-remanent magnetization and the autocorrelation of spontaneous fluctuations of magnetization, yielding acomplete determination of the fluctuation-dissipationrelation. The dynamics can be studied both in thequasi-equilibrium regime, where the fluctuation-dissipation theorem holds, and in the deeply aging regime. The limit of separation of time-scales, as used in analytical calculations, can be approached by use of a scaling procedure.