THERMOREMANENT-MAGNETIZATION RELAXATION IN THE INSULATING SPIN-GLASS CO1-XMNXCL2.2H2O

Earlier magnetization and susceptibility measurements on the mixed magnet Co1-xMnxCl2.2H2O, which has random competing short-range antiferromagnetic and ferromagnetic exchange interactions, revealed a spin-glass transition near 2.45 K over a wide composition range. The time dependence of the thermoremanent magnetization (TRM) below Tg for an x = 0.452 sample was found previously to conform approximately to decay of stretched exponential type. Small systematic deviations of data from fitted curves were apparent, however. Recently a percolation model for relaxation in random systems was proposed by Chamberlin and Haines, and shown to fit well the TRM decay in a Au:Fe spin glass and to account plausibly for relaxation in certain glasses. The model assumes dispersive excitations within fixed finite domains, and includes among its parameters the fastest and slowest relaxation rates characterizing the distribution of domains. We find that this model also leads to much better fits to the TRM decay in Co1-xMnxCl2.2H2O, with systematic deviations either eliminated or much reduced. The variation of the fitted parameters with cooling field and temperature is explored. The prefactor M(i) displays a field dependence similar to that of the TRM at arbitrary time, and a temperature dependence consistent with the independently determined T(g) value. The correlation coefficient C decreases with increasing temperature somewhat faster than 1/T. The slowest relaxation rate for the largest antialigned domain, omega+, increases with both field and temperature, while omega-, the fastest relaxation rate for the largest aligned domain, decreases with increasing temperature.