Fabrication and magnetic properties of ordered 20 nm Co-Pb nanowire arrays

Ordered Co-Pb nanowire arrays embedded in anodic alumina template were successfully fabricated by electrodeposition. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations revealed that the Co-Pb nanowires were polycrystalline with uniform diameters around 20 nm and lengths up to several micrometers. Magnetic measurements showed that the coercivity and remanence of the as-deposited Co-Pb nanowires decreased with the increase of the Pb content. After annealing the Co-Pb nanowires present higher coercivities (2.4-2.5 kOe) than that of pure Co nanowires (2.1 kOe) and the dependence of coercivity and remanence on the Pb content is inconspicuous. A phase separation of Co and Pb occurred after annealing. The familiar pinning model was employed to explain the above experimental results.     

Thermal diffusivities and molar volumes of ternary Al20 AsxTe80−x alloy glasses: evidence of self-organization

Thermal diffusivities (α) and molar volumes (V_m) of bulk Al₂₀As_xTe_80−x alloy glasses in the composition range 0≤x≤35 are examined. The results reveal a broad maximum in alpha and a broad minimum in V_m in the 15<x<25 range. Earlier temperature modulated differential scanning calorimetric measurements on these glasses have revealed the non-reversing heat flow to show a global minimum (reversibility window) in the same composition range. Taken together these results suggest that present glasses in the 15<x<25 range are self-organized. The thermal diffusivity maximum observed near x=20 is consistent with a minimal scattering of thermal waves in the homogeneous and stress-free glass composition residing in the center of the self-organized phase.     

NIR to visible upconversion emission from Dy: ZBLYAN glasses

This paper reports on the near infrared (730-783 nm) to the visible upconversion emissions at 482 nm (⁴F_9/2→⁶H_15/2), 576 nm (⁴F_9/2→⁶H_13/2) and 662 nm (⁴F_9/2→⁶H_11/2) from the Dy³⁺doped 53ZrF₄-20BaF₂-2LaF₃-2YF₃-3AlF₃-19NaF-1DyF₃ glasses. We have also carried out a systematic study on the normal emission properties of these glasses in order to understand their performance both as a NIR upconverted visible luminescent and as normal visible fluorescent optical systems of technical importance. With an increase in Dy³⁺ concentration beyond a particular value (1 mol%), activator-activator interaction becomes a significant cause of concentration quenching in the luminescence properties. The dependence of the emission spectra on the excitation wavelengths has also been examined and 451 nm was found to be the ideal excitation wavelength in the measurement of normal fluorescence spectra. In the case of NIR upconverted visible emission, we have observed that the NIR excitation at 783 nm as the suitable pump wavelength in demonstrating prominent visible emission colours from these glasses. The relevance in undertaking these optical materials lies in their potential for upconversion laser application in the visible wavelength region. The NIR upconversion phenomenon has been explained in terms of energy level schemes due to excited state absorption (ESA) and energy transfer upconversion (ETU) processes.     

Size-driven dimensional crossover in the quasi-two-dimensional Ising model

We have studied the finite size effect in the quasi-two-dimensional Ising model by using a Monte Carlo simulation. A marked finite size effect was found with decreasing interlayer interaction. Aside from the well-known three- to two-dimensional crossover, a three- to one-dimensional crossover at a crossover size L_c∼(λ/2)^−ν/φ was revealed as an origin of the marked finite size effect, where λ is the interlayer to intralayer interaction ratio, and ν and φ are the critical exponent for the correlation length and the crossover exponent, respectively. While the former crossover is driven by temperature, the latter is driven by size at a fixed λ.     

Smooth silicon oxide nanowires under supercritically hydrothermal conditions

Large-scale amorphous silicon oxide nanowires (SiONWs) have been synthesized from silicon monoxide powder under supercritically hydrothermal conditions. The SiONWs with smooth surface can reach tens of microns long. Selected area electron diffraction (SAED) shows that the samples are completely amorphous. Energy-dispersive X-ray spectrometry (EDX) analysis reveals that the SiONWs consist of Si and O elements in atomic ratio approximately to 1:1.5. Photoluminescence (PL) shows luminescence in both blue and visible. During the growth process, the H⁺ and OH⁻ blocks the defects located on the surface of the SiONWs and lead to the constant growth of the SiONWs.     

Size-dependent thermodynamic criterion for the thermal stability of binary immiscible metallic multilayers

With the aim of understanding the thermal stability of binary immiscible metallic multilayers, we propose a generally size-dependent thermodynamic criterion for determining the interface alloying in multilayers, with respect to the size-dependent interface energy of binary metal systems. Taking the copper/tungsten bilayer as an example, we obtain the interfacial alloying phase diagram based on the proposed thermodynamic model. Our theoretical predictions are consistent with experiments, implying that the size-dependent thermodynamic criterion of the thermal stability could be expected to be applicable to many multilayers.     

Polymorphic transformation of the Γ-form of d-sorbitol upon milling: structural and nanostructural analyses

In this paper, we study the structural, nanostructural and thermodynamic evolutions of crystalline Γ-sorbitol upon mechanical milling. The investigations have been performed by powder X-ray diffraction and differential scanning calorimetry. The results clearly show that the evolution upon milling can be divided in two stages. The first one only reveals micro and nanostructural modifications of the crystallites appearing through a size reduction, deformations, and changes of shape. On the other hand, the second stage reveals a complete structural transformation of the Γ-form of sorbitol towards the metastable A-form of sorbitol. Special attention has been paid to the nanostructural features derived from the first stage, which trigger the ultimate structural transformation.     

Magnetoimpedance effect of current-annealed CoNiFe/Cu microtubes

A cobalt/nickel/iron (CoNiFe) magnetic layer was electrodeposited on a 50-μm-diameter non-magnetic Cu wire in a sulphate bath using a constant voltage. Electrodeposited CoNiFe composite wires were submitted to current annealing at 540 mA. It was found that annealing time less than 1 min removes internal stresses produced during fabrication and that annealing times longer than 5 min induce circumferential anisotropy. Non-annealed sample showed a magnetoimpedance (MI) ratio of 412%. A maximum MI ratio of 583% was obtained after 1 min of current annealing.     

Spectroscopic investigation and optical characterization of novel highly thulium doped tellurite glasses

In this paper, optical properties of 75TeO₂-20ZnO-5Na₂O host glass doped with concentration of Tm³⁺ up to 10 %mol were studied in order to assess the most suitable rare earth content for short cavity fiber lasers. Raman spectroscopy revealed a change in the glass structure while increasing Tm³⁺ content, similar to the well known addition of alkali ions in a glass. Influence of the fabrication process on the OH⁻ content was determined by FTIR measurements. Refractive index of Tm³⁺ doped tellurite glasses was measured at five different wavelengths ranging from 533 nm to 1533 nm. Lifetime and emission spectra measurements of the Tm³⁺ doped tellurite glasses are reported.