AGING IN 2-DIMENSIONAL ISING SPIN-GLASSES

Aging of two-dimensional (2D) Ising spin glasses with short-range inte ractions Rb2Cu1-xCoxF4 (T(c) = 0) is studied in the critical regime vi a the low-frequency ac susceptibility and via the dc magnetization for x = 0.22 and 0.33. After quenching to low temperatures, slow logarith mic relaxation is observed for both the in-phase and out-of-phase ac s usceptibilities. Using the droplet scaling model, the spin-glass corre lation 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 microscop ic time. The exponent psi = 1.0 +/- 0.1 compares with recent theoretic al results and numerical simulations for 2D short-range Ising spin gla sses. The waiting-time dependence found for the field-cooled and zero- field-cooled dc magnetizations points to a markedly slower crossover f rom the quasiequilibrium to the nonequilibrium regime than in 3D. From experiments with different cooling histories, finally, the equilibriu m spin-glass state is inferred to be strongly dependent on the tempera ture.