  Patterned nanostructures on the order of 200 nm $\times$ 200 nm of the
itinerant ferromagnet ${\rm SrRuO_3}$ give rise to superparamagnetic behavior
below the Curie temperature (${\rm \sim 150 \ K}$) down to a sample-dependent
blocking temperature. We monitor the superparamagnetic fluctuations of an
individual volume and demonstrate that the field dependence of the
time-averaged magnetization is well described by the Langevin equation. On the
other hand, the rate of the fluctuations suggests that the volume in which the
magnetization fluctuates is smaller by more than an order of magnitude. We
suggest that switching via nucleation followed by propagation gives rise to
Langevin behavior of the total volume, whereas the switching rate is determined
by a much smaller nucleation volume.
