Neutron-diffraction study of stripe order in La{sub 2}NiO{sub 4+{delta}} with {delta}= (2) /(15)

We report a detailed neutron-scattering study of the ordering of spins and holes in oxygen-doped La{sub 2}NiO{sub 4.133}. The single-crystal sample exhibits the same oxygen-interstitial order but better defined charge-stripe order than that studied previously in crystals with {delta}=0.125. In particular, charge order is observed up to a temperature at least twice that of the magnetic transition, T{sub m}=110.5 K. On cooling through T{sub m}, the wave vector {epsilon}, equal to half the charge-stripe density within an NiO{sub 2} layer, jumps discontinuously from (1) /(3) to 0.2944. It continues to decrease with further cooling, showing several lock-in transitions on the way down to low temperature. To explain the observed lock-ins, a model is proposed in which each charge stripe is centered on either a row of Ni or a row of O ions. The model is shown to be consistent with the l dependence of the magnetic peak intensities and with the relative intensities of the higher-order magnetic satellites. Analysis of the latter also provides evidence that the magnetic domain walls (charge stripes) are relatively narrow. In combination with a recent study of magnetic-field-induced effects, we find that the charge stripes are all O centered at T{gt}T{sub m}, with amore » shift towards Ni centering at T{lt}T{sub m}. Inferences concerning the competing interactions responsible for the temperature dependence of {epsilon} and the localization of charge within the stripes are discussed. {copyright} {ital 1998} {ital The American Physical Society}« less