Dynamic susceptibility of a reentrant ferromagnet

The temperature, frequency, and magnetic-field dependence of the susceptibility of the standard reentrant ferromagnet (${\mathrm{Fe}}_{0.20}$ ${\mathrm{Ni}}_{0.80}$ ${)}_{75}$ ${\mathrm{P}}_{16}$ ${\mathrm{B}}_6$ ${\mathrm{Al}}_3$ has been investigated by ac-susceptibility measurements. In general the magnetic response is strongly nonlinear in the magnitude of the applied field h, but a distinct low-field region is found, h<${\mathit{h}}_0$, where the dynamic susceptibility does not depend on the magnitude of the field. Thus, ac-susceptibility or zero-field-cooled magnetization measurements in low enough fields, h<${\mathit{h}}_0$, allow studies of the inherent zero-field dynamics of reentrant ferromagnets. A dynamic scaling analysis of low-field dynamic susceptibility data near the ferromagnetic to reentrant spin-glass transition indicates a transition to a true spin-glass phase. Magnetic aging, another signature of spin-glass dynamics, is shown to exist in the reentrant spin-glass phase by low-field time-dependent zero-field-cooled magnetization measurements. © 1996 The American Physical Society.