  A study of magnetic avalanches in Perminvar, an Fe-Ni-Co alloy, shows that
some avalanches are almost exactly reproducible from one magnetic field cycle
to the next, while others show significant variability. Averaging over many
cycles produces a fingerprint reflecting the reproducibility of the noise. The
fingerprint is not strongly temperature or driving-rate dependent, indicating
that the variability is a consequence of dynamical effects. We also find that
the slope of the cycle-averaged magnetization, d<M>/dH, is correlated with the
cycle-to-cycle variations in magnetization, suggesting an analogy with the
fluctuation-dissipation relationship from equilibrium thermodynamics.
