  We study the temporal stability of stripe-type spin order in a layered
nickelate with X-ray photon correlation spectroscopy and observe fluctuations
on time scales of tens of minutes over a wide temperature range. These
fluctuations show an anomalous temperature dependence: they slow down at
intermediate temperatures and speed up both upon heating and cooling. This
behavior appears to be directly connected with spatial correlations: stripes
fluctuate slowly when stripe correlation lengths are large and become faster
when spatial correlations decrease. A low-temperature decay of nickelate stripe
correlations, reminiscent of what occurs in cuprates due to a competition
between stripes and superconductivity, hence occurs via loss of both spatial
and temporal correlations.
