Freezing of a stripe liquid

The existence of a stripe-liquid phase in a layered nickelate, La 1 . 7 2 5 Sr 0 . 2 7 5 NiO 4 , is demonstrated through neutron scattering measurements. We show that incommensurate magnetic fluctuations evolve continuously through the charge-ordering temperature, although an abrupt decrease in the effective damping energy is observed on cooling through the transition. The energy and momentum dependence of the magnetic scattering are parametrized with a damped-harmonic-oscillator model describing overdamped spin waves in the antiferromagnetic domains defined instantaneously by charge stripes.