Spin glasses in low DC fields. II. Magnetic viscosity

Studies of magnetic viscosity in Au-Fe alloys containing 2 at.% and 7 at.% Fe are presented. The time decays of the remanences IRM and TRM are given for a range of temperatures up to and including the spin glass temperature, Tf. All the decays are best described by the relation M=M0-Snlnt. STRM(T), SIRM(T) both have maxima at 0.6 Tf. The IRM data suggests a linear relation between S and M0. Plots of S/M0=V against T suggest the existence of two regimes of temperature below Tf: (1)T<or=0.8 Tf, VIRM nearly constant, independent of T, and much larger than VTRM. (2) 0.8<or=T<or=Tf, both VIRM and VTRM strongly dependent on T and of nearly the same magnitude. These results at low temperatures can be qualitatively reproduced using a very simple activation model for noninteracting fine particles.