Very Long Time Magnetization Decay in Spin Glasses

TL;DR

This paper discovers a third, long-term decay component in spin glass magnetization that is independent of sample history, extending understanding of aging effects to timescales of thousands of years.

Contribution

It identifies and explains a new long-time decay component in spin glasses, challenging the two-term decay model and linking it to initial state distributions during cooling.

Findings

Long time decay is independent of waiting time.

Decay follows a logarithmic pattern.

Maximum aging time estimated at around three thousand years.

Abstract

It is currently believed that the decay of the thermoremanent magnetization in spin glasses is composed of two terms; The "stationary" term which does not depend on the sample history and dominates the short time decay ($<1s$) and a long time aging term which depends on the samples history. The sample history includes both the thermal history and the time spent in a magnetic field (waiting time) before that field is removed. We report finding a third component of the decay at times much larger than the waiting time. This decay is independent of the waiting time, but part of the same mechanism that produces aging. We explain this decay in terms of the initial state distribution that is developed during the cooling process. This explanation is tested by performing Iso-thermoremanent magnetization decay measurements. Follow up calculations using the Spin Glass phase space barrier model suggest that the long time decay is logarithmic and that the maximum aging time is approximately three thousand years, in this sample, at a measuring temperature of .83 $T_{g}$.