Dynamics of the Relaxation-Time Spectrum in a CuMn Spin-Glass

SQUID magnetometry measurements on a $\mathrm{Cu}\mathrm{Mn}$ spin-glass reveal that the zero-field-cooled magnetization strongly depends on the time the sample is kept at constant temperature prior to the field application. This result is evidently at variance with the common belief that an equilibrium spin-glass state is quickly obtained after cooling in zero field. The nonequilibrium behavior, as reflected in the complex time dependence of $\frac{\partial m}{\partial \ln t}$, is interpreted to arise from slow dynamics of the relaxation-time spectrum.