Response Time Reveals Temperature Chaos in Spin Glasses

We have measured the zero field cooled magnetization M_ZFC(t) for Cu_86.5Mn_13.5 multilayer thin films of different thickness using a one-step quench protocol and two-step temperature drop protocol. The response time, t_w^eff, was extracted from the relaxation rate S(t) = dM_ZFC(t)/dlnt. We found that in the one-step temperature quench to T₂ experiments, t_w^eff was a monotonic function of waiting time t_w until the system reached a quasi-equilibrium state. In the two-step temperature drop experiments, the sample was aged at an intermediate temperature T₁ until the quasi-equilibrium state established. The temperature was then lowered to T₂, the same final temperature in one-step quench experiment. After the system regained its quasi-equilibrium state, the response time t_w^eff was compared with the maximum response time t_w^ref in one-step quench protocol. The results are rather counterintuitive: there exists a temperature range ΔT in which the two-step effective waiting times t_w^eff are either smaller or larger than t_w^ref . Above the range ΔT, t_w^eff recovers to t_w^ref. The existence of a ΔT and the recovery to reference response time may be indicative of temperature chaos in spin glasses.