RESUMO
We report the low-temperature resistance upturn in sandwiched structures of La2/3Sr1/3MnO3/ZrO2/La2/3Sr1/3MnO3 and La2/3Sr1/3MnO3/LaMnO3/La2/3Sr1/3MnO3, while it disappeared when the interlayer was replaced by YBa2Cu3O7. The experimental data have been analyzed qualitatively and quantitatively. The results show that the low temperature resistance upturn is mainly due to the quantum correction effects driven by the weak localization and the electron-electron interaction in such a strongly correlated system, and the contribution of each factor varies with grain boundaries. Moreover, the resistance upturns are suppressed by a local magnetic field. These findings will help to further understand the physical mechanism of low-temperature resistance upturn in colossal magnetoresistance manganites. Furthermore, it is also helpful to reveal the intrinsic transport mechanism at the interfaces of semiconductor/ferromagnetism and antiferromagnetism/ferromagnetism.
RESUMO
Unusual electrical transport properties associated with weak or strong localization are sometimes found in disordered electronic materials. Here, we report experimental observation of a crossover of electronic behavior from weak localization to enhanced weak localization due to the spatial influence of disorder induced by ZrO2 nanopillars in (La2/3Sr1/3MnO3)1-x:(ZrO2)x (x = 0, 0.2, and 0.3) nanocomposite films. The spatial strain regions, identified by scanning transmission electron microscopy and high-resolution x-ray diffraction, induce a coexistence of two-dimentional (2D) and three-dimentional (3D) localization and switches to typical 2D localization with increasing density of ZrO2 pillars due to length scale confinement, which interestingly accords with enhancing vertically interfacial strain. Based on the excellent agreement of our experimental results with one-parameter scaling theory of localization, the enhanced weak localization exists in metal range close to the fixed point. These films provide a tunable experimental model for studying localization in particular the transition regime by appropriate choice of the second epitaxial phase.
RESUMO
We report electronic transport measurements on high quality floating zone grown Na(x)CoO2 and Na0.41CoO2·0.6H2O single crystals. We find an in-plane electronic scattering minimum near 11 K and a clear charge ordering at approximately 50 K. The electronic and magnetic properties in hydrated and nonhydrated Na0.41CoO2 samples are similar at higher temperature, but evolve in markedly different ways below â¼50 K, where a strong ferromagnetic tendency is observed in the hydrated sample. Model calculations show the relationship of this tendency to the structure of the Fermi surface. The results, particularly the clear differences between the hydrated and nonhydrated material show a substantially enhanced ferromagnetic tendency upon hydration. Implications for superconductivity are discussed.