  In the iron--chromium system, Fe$_{x}$Cr$_{1-x}$, a wide dome of spin-glass
behavior emerges when the ferromagnetism of iron is suppressed and the
antiferromagnetism of chromium emerges as a function of increasing iron content
$x$. As both, the high-temperature state and the characteristic cluster size
vary as a function of $x$, different regimes of spin-glass behavior may be
compared in a single, isostructural material system. Here, we report a study of
the spin dynamics across the freezing process into the spin-glass state for
different iron concentrations ($x = 0.145$, $0.175$, $0.21$) using Modulation
of IntEnsity with Zero Effort (MIEZE) spectroscopy. In the parameter range
studied, the relaxation process observed experimentally may be described well
in terms of a stretched exponential. In the reentrant cluster-glass regime, $x
= 0.145$, this behavior persists up to high temperatures. In comparison, in the
superparamagnetic regime, $x = 0.175$ and $x = 0.21$, a single relaxation time
at elevated temperatures is observed. For all samples studied, the spin
relaxation exhibits a momentum dependence consistent with a power law,
providing evidence of a dispersive character of the spin relaxation.
