V. Sachan

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(2)NiO(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 d = 0.125. In particular, charge order is observed up to a temperature at least twice that of the magnetic transition, T_m = 110.5 K. On cooling through T_m, the wave vector \epsilon, equal to half the charge-stripe density within an NiO(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>T_m, with a shift towards Ni centering at T<T_m. Inferences concerning the competing interactions responsible for the the temperature dependence of \epsilon and the localization of charge within the stripes are discussed.

Study of phases formed during production of copper indium diselenide by reacting copper, indium and selenium layers

Abstract CuInSe 2 films were grown by reacting stacked layers of Cu, In and Se in an atmosphere of Se vapor. Incremental growth of the various phases was followed at different temperatures until a single phase CuInSe 2 film was formed. Conventional X-ray diffraction was used in identifying the different phases formed. Along with the knowledge of different phases formed at increasing reaction temperatures, it was concluded that CuInSe 2 is formed at temperatures as low as 235°C, although a single phase film is obtained only at higher temperatures (≈350°C).

Ordering of holes and spins in La2NiO4.125 and La1.8Sr0.2NiO4

Abstract Single-crystal neutron diffraction studies of La2NiO4.125 and La1.8Sr0.2NiO4 reveal evidence for a long-period-commensurate coupled ordering of spins and charges below approximately 110 K. Analysis of the superlattice peaks indicates that the dopant-induced holes order in domain walls that form antiphase boundaries between antiferromagnetic stripes.

Stripe order of holes and spins in oxygen-doped nickelates

La{sub 2}NiO{sub 4} is a Mott-Hubbard insulator consisting of antiferromagnetic NiO{sub 2} planes alternating with La{sub 2}O{sub 2} layers. The NiO{sub 2} planes can be doped with holes. There is now considerable evidence that the insulating behavior occurs because the dopant-induced holes tend to order themselves in periodically spaced stripes. The authors present a detailed neutron scattering study of the ordering of spins and holes in oxygen doped La{sub 2}NiO{sub 4.133}. The temperature dependence of the stripe spacing, the width of the stripes and the extent of their pinning to the lattice are investigated.

Stoichiometry, Structure, and Properties of La2NiO4+δ and La2-xSrxNiO4±δ

The oxygen content phase diagram of La2NiO4+δ has been studied in detail using x-ray and neutron diffraction data from well-characterized specimens. There are numerous phase separations and phase transitions which are observed with changes in temperature and composition. The complexity of the phase diagram arises primarily from oxygen defect interactions, however we have also obtained evidence for coupled charge and spin ordering at δ= 0.125 corresponding to organization of holes into ordered domain walls. These domain walls act as antiphase boundaries between stripes of antiferromagnetically ordered nickel moments. Neutron scattering data on Sr-substituted compositions with well-defined oxygen content indicate incommensurate charge and spin correlations closely related to those in the x = 0, δ= 0.125 composition. The incommensurability approaches 1/4 and the correlation length increases as the hole concentration approaches p = x + 2δ = 0.25.