Magnetization reversal of ferromagnetic nanosprings affected by helical shape.

Helicity, a natural property of macro-, micro-, and nano-objects, potentially offers a new dimension to mechanical and electromagnetic applications for creating emerging nanodevices, such as nanorobots, nanomagnets, nanosensors, and high-density magnetic memory. Helical magnetic nanosprings are unique objects with remarkable magnetic properties, including the absence of stray fields in remanence owing to the chiral geometry, which makes them promising for data storage devices, nanoelectromechanical systems, and biomedical usage. Here, we investigated Co and CoFe nanospring arrays electrodeposited in highly ordered nanoporous templates. We report helical-shape-driven magnetization reversal of the nanosprings in comparison with the behavior of dipolarly coupled nanowires. We reveal two magnetization reversal modes depending on the orientation of the external magnetic field: coherent rotation of magnetization in the longitudinal geometry and three-dimensional vortex domain wall motion in the transverse geometry. The experimental findings are supported by analytical calculations and micromagnetic simulations that help to explain the field-dependent spin configurations observed by magnetic force microscopy.

MnO2 Nanowire-CeO2 Nanoparticle Composite Catalysts for the Selective Catalytic Reduction of NO x with NH3.

MnO x-based catalysts have been applied to the selective catalytic reduction of NO x with ammonia (NH3) owing to their high NO x removal efficiency and catalytic stability. In general, the fabrication of a variety of nanomaterials in a complex structure requires complicated processes, including heat treatment and a series of cleaning steps. In addition, MnO2 which has diverse polymorphs, exhibits different catalytic effects depending on its crystalline structure. Among them, synthesizing the ε-MnO2 phase, which functions as a nanocatalyst, has been the most difficult and has hardly been reported. Here, we report the synthesis of heterostructured composite nanocatalysts consisting of ε-MnO2 nanowires (NWs) and CeO2 nanoparticles (NPs) by applying pulsed currents sequentially. This method drastically simplifies the overall process compared to the conventional techniques. Through X-ray diffraction and transmission electron microscopy, it was confirmed that 2-3 nm of CeO2 NPs were formed on the surfaces of the ε-MnO2 NWs. The de-NO x efficiency of the nanocatalysts was analyzed in terms of content variation, specific surface area, and the elemental chemical state of the surface. A ceramic filter containing the nanocatalysts shows a high catalytic activity over the broad operating temperature range 100-400 °C. In the low-temperature region, ε-MnO2 plays a major role in determining the catalytic property, which is consistent with the Brunauer-Emmett-Teller (BET), H2 temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) results. On the other hand, in the high-temperature region, the efficiency increases gradually as the content of CeO2 increases. The H2 TPR, NH3-temperature-programmed desorption, and XPS patterns reveal why the composite exhibits such superior characteristics in the temperature range mentioned above.

Synthesis of Co nanotubes by nanoporous template-assisted electrodeposition via the incorporation of vanadyl ions.

We report a facile fabrication concept for nanotubes (NTs) based upon template-assisted electrodeposition, which is widely applied for metallic nanowire (NW) synthesis. Co NTs have been synthesized into nanoporous anodized aluminum oxide (AAO) templates via electrodeposition by simply adding a small amount of chemicals including vanadyl ions (VO2+).

Synthesis of Fe Doped ZnO Nanowire Arrays that Detect Formaldehyde Gas.

Owing to their chemical and thermal stability and doping effects on providing electrons to the conduction band, doped ZnO nanowires have generated interest for use in electronic devices. Here we report hydrothermally grown Fe-doped ZnO nanowires and their gas-sensing properties. The synthesized nanowires have a high crystallinity and are 60 nm in diameter and 1.7 µm in length. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are employed to understand the doping effects on the microstructures and gas sensing properties. When the Fe-doped ZnO nanowire arrays were evaluated for gas sensing, responses were recorded through changes in temperature and gas concentration. Gas sensors consisting of ZnO nanowires doped with 3-5 at.% Fe showed optimum formaldehyde (HCHO) sensing performance at each working temperature.