Activated dynamics in a two-dimensional Ising spin glass:Rb2Cu1−xCoxF4

Abstract

The complex ac susceptibility of the two-dimensional Ising spin glass ${\mathrm{Rb}}_{2}$${\mathrm{Cu}}_{0.782}$${\mathrm{Co}}_{0.218}$${\mathrm{F}}_{4}$ is measured as a function of the temperature and frequency. The results are first analyzed in terms of the Cole-Cole formalism. It is found that the median relaxation time ${\ensuremath{\tau}}_{c}$ diverges towards ${T}_{c}$=0 K over as many as 16 decades according to activated dynamics, i.e., ${\ensuremath{\tau}}_{c}$\ensuremath{\propto}exp[(b/T${)}^{1+\ensuremath{\psi}\ensuremath{\nu}}$]. The distribution of relaxation times appears to be nearly symmetric in ln\ensuremath{\tau}, covering at least 10 decades in width. These findings are corroborated with analyses based on exponential-logarithmic and stretched-exponential forms of the time decay of the spin-spin correlation function. The out-of-phase susceptibility is further found to be in conformity with activated dynamic scaling over a wide range of temperatures and frequencies. For the critical exponents the various methods of analysis yield, on the average, \ensuremath{\gamma}=4.4\ifmmode\pm\else\textpm\fi{}0.2, \ensuremath{\nu}=2.4\ifmmode\pm\else\textpm\fi{}0.3, \ensuremath{\theta}=-0.41\ifmmode\pm\else\textpm\fi{}0.05, and \ensuremath{\psi}=0.8\ifmmode\pm\else\textpm\fi{}0.2.