Hierarchically structured nanowires on and nanosticks in ZnO microtubes.

We report both coaxial core-shell structured microwires and ZnO microtubes with growth of nanosticks in the inner and nanowires on the outer surface as a novel hierarchical micro/nanoarchitecture. First, a core-shell structure is obtained-the core is formed by metallic Zn and the semiconducting shell is comprised by a thin oxide layer covered with a high density of nanowires. Such Zn/ZnO core-shell array showed magnetoresistance effect. It is suggested that magnetic moments in the nanostructured shell superimposes to the external magnetic field enhancing the MR effect. Second, microtubes decorated with nanowires on the external surface are obtained. In an intermediate stage, a hierarchical morphology comprised of discrete nanosticks in the inner surface of the microtube has been found. Hyperfine interaction measurements disclosed the presence of confined metallic Zn regions at the interface between linked ZnO grains forming a chain and a ZnO thicker layer. Surprisingly, the metallic clusters form highly textured thin flat regions oriented parallel to the surface of the microtube as revealed by the electrical field gradient direction. The driving force to grow the internal nanosticks has been ascribed to stress-induced migration of Zn ions due to compressive stress caused by the presence of these confined regions.

The effect of hybridization on local magnetic interactions at highly diluted Ce ions in tetragonal intermetallic compounds RERh2Si2 (RE=Ce, Pr, Nd, Gd, Tb, Dy).

The contribution of the 4f electron to the local magnetic field at highly diluted Ce atoms in RERh(2)Si(2) (RE = Ce, Pr, Nd, Gd, Tb, Dy) has been investigated as a function of temperature through the measurement of the magnetic hyperfine field in (140)Ce nuclei by time differential perturbed gamma-gamma angular correlation spectroscopy. Samples of the studied compounds were characterized by x-ray diffraction and zero-field resistance to determine the crystal structure and transport properties. DC magnetic susceptibility was measured for NdRh(2)Si(2). It was observed that the variation of the magnetic hyperfine field with temperature follows the expected behaviour for the host magnetization, with the exception of GdRh(2)Si(2), which showed a strong deviation from such a behaviour. It is shown that the hybridization of the d band of the host with the f band of the Ce impurity, which is stronger in GdRh(2)Si(2) than in other compounds, is responsible for the observed deviation from the expected temperature dependence of the hyperfine field. The origin of this stronger hybridization is ascribed to the relatively small magnetic anisotropy observed in GdRh(2)Si(2) when compared with the other compounds of the series, as shown by resistance measurements.