  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.
