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.

• Received 2 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.2340