  By means of spin current, the flow of spin angular momentum, we find a regime
of "spin treacle" in a frustrated magnetic system. To establish its existence,
we have performed spin transport measurements in nanometer-scale spin glasses.
At temperatures high enough that the magnetic moments fluctuate at high
frequencies, the spin Hall angle, the conversion yield between spin current and
charge current, is independent of temperature. The spin Hall angle starts to
decrease at a certain temperature $T^{*}$ and completely vanishes at a lower
temperature. We argue that the latter corresponds to the spin freezing
temperature $T_{\rm f}$ of the nanometer-scale spin glass, where the direction
of conduction electron spin is randomized by the exchange coupling with the
localized moments. The present experiment \textit{quantitatively} verifies the
existence of a distinct "spin treacle" between $T_{\rm f}$ and $T^{*}$. We have
also quantified a time scale of fluctuation of local magnetic moments in the
spin treacle from the spin relaxation time of conduction electrons.
