[en] Exchange enhancement through thermal anneal in bottom-pinned Mn₇₆Ir₂₄ spin valves is investigated. Samples were fabricated by ion beam deposition (IBD), post-annealed in vacuum (10^-6Torr) at 270 degreeC for 10 min, then cooled in a 3 kOe applied field. For a bilayer structure, glass/Ta 40 Aa/NiFe 30 Aa/MnIr 60 Aa/CoFe 25 Aa/Ta 40 Aa, the exchange field (H_ex) reaches 1148 Oe (J_ex=0.4erg/cm²) after anneal. X-ray diffraction (XRD) analysis shows strong enhancement of <111> texture upon anneal, while grain size obtained from XRD and transmission electron microscopy for as-deposited and annealed states shows no major change. With increasing MnIr thickness, the exchange field decreases, and blocking temperature (T_b) increases, reaching 295 degreeC for t_MnIr=180Aa. Spin valves built with the same exchange bilayer (Ta 20 Aa/NiFe 30 Aa/MnIr 60 Aa/CoFe 25 Aa/Cu 22 Aa/CoFe 20 Aa/NiFe 40 Aa/Ta 40 Aa) show H_ex=855Oe (J_ex=0.3erg/cm²) and magnetoresistance (MR)=7.1%. The incorporation of nano-oxide layers in spin valves increases the MR signal to 11%. No signal degradation is found in these specular structures for anneals up to 310 degreeC. [copyright] 2001 American Institute of Physics

[en] Graphical abstract: (a) TEM image and (b) Polyhedral representation of ZrV_1.6Mo_0.4O_7.2; (c) Thermal expansion curves and (d) Degradation curves of ZrV_2−xW_xO_7+δ (x = 0, 0.1, 0.2, 0.3, and 0.4). - Highlights: • Novel ZrV_2−xW_xO_7+δ solid solutions were first prepared by sol–gel method. • W⁶⁺ doping has influence on the crystal structure. • ZrV_1.6W_0.4O_7.2 shows negative thermal expansion during its corresponding temperature. • W⁶⁺ doped ZrV₂O₇ exhibits superior photocatalytic active than that of pure sample. - Abstract: Tungsten-doped ZrV₂O₇ having good photoactivities under UV-light excitation for the degradation of Rhodamine B has been synthesized by sol–gel method. As-prepared samples were examined by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV–vis absorption and photoluminescence spectroscopy. From the structural and morphological characterization it has been stated that the presence of W⁶⁺ induces the progressive stabilization of normal phase with 1 × 1 × 1 cubic structure (centric space group Pa3^¯ (Z = 4)). ZrV_1.6W_0.4O_7.2 shows negative thermal expansion (NTE) at room temperature while ZrV_2−xW_xO_7+δ with other ratios show positive thermal expansion. Mechanism for this change in thermal expansion property was discussed. ZrV_1.6W_0.4O_7.2 also exhibits best photocatalytic performance, the reason is that the occurrence of W⁶⁺ doping ZrV₂O₇ system ZrV₂O₇ system induces the higher photocatalytic activities by promoting the separation of photo-induced electron-hole pairs. PL analysis provides clear evidence of the lower charge carrier recombination in tungsten-doped systems

[en] ZrWMoO₈ rods with negative thermal expansion and ZrWMoO₈/Ag composites with core–shell structure were first proved to exhibit photocatalytic activity under UV-irradiation. Highlights: ► ZrWMoO₈ rods with negative thermal expansion property were first studied for its photocatalytic activity. ► ZrWMoO₈/Ag composites with core–shell structure were prepared using a simple reduction method. ► Improved photocatalytic activity was found in the ZrWMoO₈/Ag heterostructures. ► The ZrWMoO₈/Ag heterostructure promotes the separation of electron–hole pairs and enhances the photocatalytic activity. - Abstract: A novel photocatalytic ZrWMoO₈/Ag composite with core–shell structure was prepared. The composites were composed of ZrWMoO₈ rods with negative thermal expansion (NTE) property as cores and Ag nanoparticles as shell. The resulting products were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectrophotometer (UV–vis DRS). The results showed that ZrWMoO₈ rods displayed not only negative thermal expansion but also photocatalytic efficiency toward Rhodamine B (RB) degradation under UV-irradiation. The as-prepared ZrWMoO₈/Ag composites exhibited a higher photocatalytic activity than that of pure ZrWMoO₈, thereby implying that the ZrWMoO₈/Ag interfaces promote the separation of photogenerated electron–hole pairs and enhance the photocatalytic activity.

[en] In this paper, we propose a novel polarization conversion mechanism based on bianisotropic response of split ring resonator (SRR) metamaterial. It is found that under oblique incidence condition with the incident terahertz electric field parallel to the SRR gap, the magnetic field component of the incident wave can excite the fundamental LC resonance of SRR and form an electric dipole perpendicular to the SRR gap, which radiates orthogonal electric field thus resulting in polarization conversion. Numerical simulations and experiments are performed to verify this idea and the results are in excellent agreement. This study contributes to our understanding of the bianisotropic electromagnetic response of SRR and opens new opportunities for creating high-efficiency and low-loss polarization conversion devices in THz or other frequencies using bianisotropic metamaterials. (paper)

[en] Novel ZrV₂O₇ microfibers with diameters about 1–3 μm were synthesized using a sol–gel technique. For comparison, ZrV₂O₇ powders were prepared by the same method. The resultant structures were studied by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that both the pure ZrV₂O₇ microfibers and powders could be synthesized by the sol–gel technique. The thermal expansion property of the as-prepared ZrV₂O₇ microfibers and powders was characterized by a thermal mechanical analyzer, both the fibers with cylindrical morphology and irregular powders with average size between 100 and 200 nm showed negative thermal expansion between 150 °C and 600 °C. The photocatalytic activity of the microfibers was compared to that of powders under UV radiations. The band gap of ZrV₂O₇ microfibers decreased and its absorption edge exhibited red shift. The microfibers also had a higher surface area compared with the powders, resulting in considerably higher photocatalytic characteristics. The large surface area and the enhanced photocatalytic activity of the ZrV₂O₇ microfibers also offer potential applications in sensors and inorganic ion exchangers. - Graphical abstract: (a and c) SEM photos of ZrV₂O₇ powders and fibers. (b and d) TEM images of ZrV₂O₇ powders and fibers. (e) Thermal expansion curves of ZrV₂O₇ powders and fibers. (f) Degradation curves of ZrV₂O₇ powders and ZrV₂O₇ fibers. - Highlights: • Novel ZrV₂O₇ fibers could be synthesized using sol–gel technique. • ZrV₂O₇ powders with irregular shape are also prepared for comparison. • Both ZrV₂O₇ microfibers and powders exhibit negative thermal expansion property. • ZrV₂O₇ microfibers show outstanding photocatalytic activity under UV irradiation. • This synthesis technique can be easily extended to many other functional fibers

[en] Highlights: ► The ZnO/PbSe core-shell nanorod arrays were fabricated by a two-step electrodeposition method from aqueous solution for the first time. ► The absorption spectrum of ZnO/PbSe shows visible light absorption from 500 nm to 650 nm due to the PbSe coating. ► PbSe nanotube arrays were obtained by immersing the ZnO/PbSe core-shell nanorods arrays in hydrochloric acid for 10 min. - Abstract: The ZnO/PbSe core-shell nanorod arrays were fabricated by a two-step electrodeposition method from aqueous solution for the first time. The synthesized core-shell nanorod arrays were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained samples share the characters of both ZnO and PbSe in XRD patterns. The SEM images show that the average diameter and length of ZnO nanorods are 120–200 nm and 2.5 μm, respectively. The TEM images show that these heterostructured nanorods are made up of two parts, a single crystalline ZnO nanorod with a [0 0 1] growth direction as the core and crystalline PbSe layer as the shell. The absorption spectrum of ZnO/PbSe shows visible light absorption from 500 nm to 650 nm due to the PbSe coating. In addition, the PbSe nanotube arrays were fabricated by immersing the heterostructures in hydrochloric acid, which were characterized by SEM and TEM. SEM images show that the average diameter of these nanotubes is 250 nm and the average thickness of their walls is about 75 nm. TEM images show that the PbSe nanotubes exhibit polycrystalline structure.

[en] Magnetic multilayer structures are key components in devices used for magnetic information storage and sensing. Application in such devices relies on the ability to precisely control the switching characteristics and the magnetic coupling between the layers. The magnetic and transport properties of the device are governed by the composition, structure and thickness of the various layers which make up the multilayer stack as well as the quality of the interfaces between the layers. Advanced analytical electron microscopy techniques are used to investigate the structure and composition of layers in two different types of spin tunnel junction stacks and in perpendicular spin valve stacks. High angle annular dark field scanning transmission electron microscopy imaging combined with electron energy loss spectroscopy spectrum imaging provides rapid coverage of large areas of material along with precise chemical information from specific regions of interest. This combination of techniques is shown to be particularly useful for examining the oxide barrier layers and the extent of any oxidation defects within the layer stacks