Probing Spin Glass Energy Landscapes with 1/f Noise

Abstract

The spin-glass transition is a dynamical phase transition, similar in nature to that of structural glasses and other systems. Upon quenching from above the transition temperature Tg to a measurement temperature T < Tg, experiments and simulations have unveiled an underlying length scale, the spin-glass correlation length, that grows very slowly with time. The time-dependent growth correlation length is key to the observed dynamics and to the understanding of the underlying energy barrier distribution. Analysis of our measurements provides the first explicit determination of the evolution of the spin-glass energy barrier distribution as a function of film thickness and temperature. By fabricating samples of multiple thicknesses, and allowing the correlation length to grow to the sample thickness on experimental timescales, it becomes possible to extract information about the length dependence of the energy barriers. We have made measurements of the 1/f noise in the resistance of spin-glass films of five thicknesses. These results are consistent with the limited earlier thin film measurements, despite the use of a different cooling protocol. A recent analysis, based on simulations of mesoscale samples with a number of spins comparable to those under experimental study, provided an explanation for the barrier growth in the earlier measurements, but suggested that our cooling protocol would have produced very different dynamics, consistent with activation over a single, temperature-independent barrier distribution, which we do not observe. This suggests that either the growth of in-plane correlations are playing a role, or that the explanation for the barrier growth in the earlier measurements applies to our measurements in spite of our cooling protocol.