AGING IN 2-DIMENSIONAL ISING SPIN-GLASSES

Aging of two-dimensional (2D) Ising spin glasses with short-range interactions Rb2Cu1-xCoxF4 (T(c) = 0) is studied in the critical regime via the low-frequency ac susceptibility and via the dc magnetization for x = 0.22 and 0.33. After quenching to low temperatures, slow logarithmic relaxation is observed for both the in-phase and out-of-phase ac susceptibilities. Using the droplet scaling model, the spin-glass correlation length R is concluded to increase after a temperature quench as R is-proportional-to (ln (t))1/psi, with t in units of some microscopic time. The exponent psi = 1.0 +/- 0.1 compares with recent theoretical results and numerical simulations for 2D short-range Ising spin glasses. The waiting-time dependence found for the field-cooled and zero-field-cooled dc magnetizations points to a markedly slower crossover from the quasiequilibrium to the nonequilibrium regime than in 3D. From experiments with different cooling histories, finally, the equilibrium spin-glass state is inferred to be strongly dependent on the temperature.