Lack of Out-of-Plane Dispersion of the Magnetic Excitations of Charge-Stripe Ordered La2−xSrxNiO4+δ

The dependence of the magnetic excitations in the out-of-NiO-plane direction of charge stripe ordered La2-xSrxNiO4+delta x = 0.3 and delta = 0.11 +/- 0.01 were investigated by inelastic neutron scattering. No dispersion was observed for the magnetic excitations in the out-of-plane (0, 0, l) direction of reciprocal space of La2-xSrxNiO4+delta, indicating an upper limit of the out-of-plane spin interaction of J(perpendicular to) < 0.25 meV.