Chaos in the Ferromagnetic Phase of a Reentrant Ferromagnet

The inherent dynamic properties of the ferromagnetic phase of a reentrant ferromagnet, (F${\mathrm{e}}_{0.20}$N${\mathrm{i}}_{0.80}$ ${)}_{75}$ ${\mathrm{P}}_{16}$ ${\mathrm{B}}_6$A${\mathrm{l}}_3$, have been experimentally investigated by low field magnetic relaxation and ac susceptibility measurements. A prominent aging behavior and an apparent fatal fragility to temperature fluctuations imply that the ferromagnetic phase of the reentrant system has a chaotic nature similar to the spin glass phase, but in striking contrast to the robust nature of the regular ferromagnetic phase.