We have observed a diffuse component to the low-energy magnetic excitation spectrum of stripeordered La 5/3 Sr 1/3 NiO4 probed by neutron inelastic scattering. The diffuse scattering forms a square pattern with sides parallel and perpendicular to the stripe directions. The signal is dispersive, with a maximum energy of ∼ 10 meV. Probed at 2 meV the scattering decreases in strength with increasing temperature, and is barely visible at 100 K. We argue that the signal originates from dynamic, quasione-dimensional, antiferromagnetic correlations among the stripe electrons.PACS numbers: 75.40. Gb, 71.45.Lr, 75.30.Et, 75.30.Fv The occurence of stripe correlations in superconducting cuprates and other doped antiferromagnets is well established from extensive experimental studies [1] following earlier theoretical work [2]. The stripe phase is characterized by a segregation of charge carriers into narrow channels that act as antiphase domain walls separating antiferromagnetic regions of the host spins. Several theoretical scenarios have been presented in which a spin gap and pairing instabilities appear among the stripe electrons, opening the door to superconductivity [3]. These findings suggest that stripes could play an important role in the physics of high-T c superconductivity.Given the characteristic spin and charge correlations associated with local stripe order it is natural to search the spin excitation spectrum for clues to the relationship between stripes and superconductivity. Neutron inelastic scattering has revealed a number of interesting features in the spin dynamics of the cuprate superconductors, some of which, e.g. excitations at incommensurate wavevectors [4], have been interpreted as evidence for dynamic stripe correlations [5]. At the same time, the characteristic spin excitation spectrum of ideal stripes has been probed in studies of non-superconducting compounds with well defined stripe order, especially La 2−x Sr x NiO 4+δ [6,7]. In none of these previous studies, however, has any evidence been found for spin correlations among the stripe electrons themselves.In this paper we report neutron inelastic scattering measurements on La 5/3 Sr 1/3 NiO 4 which reveal a pattern of inelastic diffuse scattering consistent with the existence of quasi-one-dimensional (1D) antiferromagnetic (AF) correlations parallel to the stripe direction. The correlations are found to be dynamic, with a maximum energy ∼ 10 meV. The results provide the first evidence for spin correlations among the charge carriers in a stripe phase.The experiments were performed on single crystals of La 5/3 Sr 1/3 NiO 4 grown by the floating-zone method [8]. Neutron inelastic scattering data were collected on the triple-axis spectrometers IN8, IN20 and IN22 at the Institut Laue-Langevin, and RITA-II at the Paul Scherrer Institut. Most of the data reported here were obtained with a fixed scattered neutron energy E f = 14.7 meV and with a graphite filter installed after the sample to suppress higher orders. The exception is the inelastic sca...