Temperature chaos in a Ge:Mn thin-film spin glass

Abstract

Temperature changes in thin-film Ge:Mn spin-glass dynamics are presented that exhibit temperature chaos (TC) when the spin-glass correlation length $\ensuremath{\xi}(t,T)$ grows to its thickness $\mathcal{L}$. For small $\mathcal{L}\ensuremath{\approx}15.5$ nm, the transition to chaos takes place over a temperature range $\mathrm{\ensuremath{\Delta}}T$ sufficiently large to exhibit both reversible and chaotic behavior. The value of $\mathrm{\ensuremath{\Delta}}T$ can be related to the critical exponent for TC, $\ensuremath{\zeta}$. Experimentally, $\ensuremath{\zeta}$ is found to be $\ensuremath{\approx}1.06$, in the range of recent simulations. The presence of a specific length scale $\mathcal{L}$ allows the transition to chaos to be examined over measurable laboratory temperature changes. The transition is found to be abrupt. Bulk materials, with a distribution of crystallite sizes, will smear out the transition, resulting in a very slow crossover. The abruptness of the transition and its nature are compared with recent theoretical calculations.