Absence of rejuvenation in a Superspin Glass

TL;DR

This study investigates the nonequilibrium dynamics of superspin glasses under temperature variations, revealing strong cooling effects, absence of temperature-chaos, and explaining aging and relaxation phenomena through a real space droplet model.

Contribution

It provides new insights into superspin glass dynamics, showing differences from atomic spin glasses and explaining aging and relaxation with a real space droplet framework.

Findings

No evidence for temperature-chaos in superspin glasses.

Strong cooling rate effects are observed unlike atomic spin glasses.

Cumulative aging can be explained by length scales shorter than the chaos overlap length.

Abstract

Effects of temperature changes on the nonequilibrium spin-glass dynamics of a strongly interacting ferromagnetic nanoparticle system (superspin glass) are studied. In contrary to atomic spin glasses, strong cooling rate effects are observed, and no evidence for temperature-chaos is found. The flip time of a magnetic moment is much longer than that of an atomic spin and hence much shorter time scales are probed within the experimental time window for a superspin glass than for an atomic spin glass. Within a real space picture the cumulative aging observed for the superspin glass can be explained considering that all investigated length scales are shorter than the temperature-chaos overlap length. The transient relaxation, observed in experiments after temperature changes, can be understood as the adjustment of thermally active droplets, which is mutatis mutandis the Kovacs effect observed in most glassy systems.