Domain growth by aging in nonequilibrium two-dimensional random Ising systems

The ac susceptibility in the two-dimensional Ising spin glass ${\mathrm{Rb}}_2$ ${\mathrm{Cu}}_{0.67}$ ${\mathrm{Co}}_{0.33}$ ${\mathrm{F}}_4$ and the two-dimensional random-exchange Ising ferromagnet ${\mathrm{Rb}}_2$ ${\mathrm{Cu}}_{0.89}$ ${\mathrm{Co}}_{0.11}$ ${\mathrm{F}}_4$ is observed to relax towards equilibrium on a time scale of hours following fast quenching to 3.9 K. Scaling of the in-phase and out-of-phase susceptibilities yields that the ordered domains grow according to (lnt${)}^{1/\mathrm{\psi }}$, with t expressed in units of a microscopic time, and ψ=1.07±0.10 and 0.20±0.05, respectively. Both values are in agreement with recent theoretical results and numerical simulations.