  We propose an experiment to probe ferromagnetic phenomena in an ultracold
Fermi gas, while alleviating the sensitivity to three-body loss and competing
many-body instabilities. The system is initialized in a small pitch spin
spiral, which becomes unstable in the presence of repulsive interactions. To
linear order the exponentially growing collective modes exhibit critical
slowing down close to the Stoner transition point. Also, to this order, the
dynamics are identical on the paramagnetic and ferromagnetic sides of the
transition. However, we show that scattering off the exponentially growing
modes qualitatively alters the collective mode structure. The critical slowing
down is eliminated and in its place a new unstable branch develops at large
wave vectors. Furthermore, long-wavelength instabilities are quenched on the
paramagnetic side of the transition. We study the experimental observation of
the instabilities, specifically addressing the trapping geometry and how
phase-contrast imaging will reveal the emerging domain structure. These probes
of the dynamical phenomena could allow experiments to detect the transition
point and distinguish between the paramagnetic and ferromagnetic regimes.
