Spin Dynamics in an Ordered Stripe Phase

Inelastic neutron scattering has been used to measure the low-energy spin excitations in the ordered charge-stripe phase of ${{\mathrm{La}}_2\mathrm{NiO}}_{4+\delta }$ with $\delta =0.133\mathrm{}$. Spin-wave-like excitations disperse away from the incommensurate magnetic superlattice points with a velocity $\sim 60\%$ of that in the $\delta =0\mathrm{}$ compound. Incommensurate inelastic peaks remain well resolved up to at least twice the magnetic ordering temperature. Paramagnetic scattering from a $\delta =0.105\mathrm{}$ sample, which has a Néel-ordered ground state, shows anomalies suggestive of incipient stripe correlations. Similarities between these results and measurements on superconducting cuprates are discussed.