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

Earlier magnetization and susceptibility measurements on the mixed mag net Co1-xMnxCl2.2H2O, which has random competing short-range antiferro magnetic and ferromagnetic exchange interactions, revealed a spin-glas s transition near 2.45 K over a wide composition range. The time depen dence of the thermoremanent magnetization (TRM) below Tg for an x = 0. 452 sample was found previously to conform approximately to decay of s tretched exponential type. Small systematic deviations of data from fi tted curves were apparent, however. Recently a percolation model for r elaxation 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 dispers ive excitations within fixed finite domains, and includes among its pa rameters the fastest and slowest relaxation rates characterizing the d istribution of domains. We find that this model also leads to much bet ter fits to the TRM decay in Co1-xMnxCl2.2H2O, with systematic deviati ons either eliminated or much reduced. The variation of the fitted par ameters with cooling field and temperature is explored. The prefactor M(i) displays a field dependence similar to that of the TRM at arbitra ry time, and a temperature dependence consistent with the independentl y determined T(g) value. The correlation coefficient C decreases with increasing temperature somewhat faster than 1/T. The slowest relaxatio n 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.