Electrodeposition of hexagonal Co nanowires with large magnetocrystalline anisotropy

Effect of Growth Rate on the Crystal Orientation and Magnetization Performance of Cobalt Nanocrystal Arrays Electrodeposited from Aqueous Solution

The formation work of a two-dimensional hcp-Co (metallic cobalt crystal with hexagonal close packed structure) nucleus, W_hkl, was calculated by Pangarov's theory. W₀₀₂ was estimated to be smaller than W₁₀₀ in a cathode potential range nobler than the transition potential, E^tra (ca. -0.77 V vs. Ag/AgCl). To confirm the above estimation, ferromagnetic nanocomposite thick films, which contained (002) textured hcp-Co nanocrystal arrays, were synthesized by potentiostatic electrochemical reduction of Co²⁺ ions in anodized aluminum oxide (AAO) nanochannel films with ca. 45 µm thickness. The aspect ratio of hcp-Co nanocrystals with a diameter of ca. 25 nm reached up to ca. 1800. Our experimental results revealed that the texture coefficient, TC₀₀₂, increased when decreasing the overpotential for hcp-Co electrodeposition by shifting the cathode potential nobler than E^tra. In a similar way, TC₀₀₂ increased sharply by decreasing the growth rate of the hcp-Co nanocrystals so that it was smaller than the transition growth rate, R^tra (ca. 600 nm s^-1). The perpendicular magnetization performance was observed in AAO nanocomposite films containing hcp-Co nanocrystal arrays. With increasing TC₀₀₂, the coercivity of the nanocomposite film increased and reached up to 1.66 kOe, with a squareness of ca. 0.9 at room temperature.

Flexural Properties and Fracture Behavior of Nanoporous Alumina film by Three-Point Bending Test

This study investigated the influence of porosity on the flexural property of a nanoporous alumina film. When the porosity of the alumina film increased, both bending strength and modulus declined. The results from the bending test revealed that the setting of the film during the bending test had significant influence on the flexural property. Fracture only occurred when the porous side of the alumina film suffered tensile stress. The ability to resist fracture in the barrier layer was higher than in the porous side; the magnitude of the bending strength was amplified when the barrier layer sustained tensile stress. When the porous layer suffered a tensile stress, the bending strength decreased from 182.4 MPa to 47.7 Mpa as the porosity increased from 22.7% to 51.7%; meanwhile, the modulus reduced from 82.7 GPa to 17.9 GPa. In this study, the most important finding from fractographic analysis suggested that there were a localized plastic deformations and layered ruptures at the porous side of the alumina film when a load was applied. The fracture behavior of the nanoporous alumina film observed in the present work was notably different from general ceramic materials and might be related to its asymmetric nanostructure.

High energy product developed from cobalt nanowires

Cobalt nanowires with high aspect ratio have been synthesized via a solvothermal chemical process. Based on the shape anisotropy and orientation of the nanowire assemblies, a record high room-temperature coercivity of 10.6 kOe has been measured in Co nanowires with a diameter of about 15 nm and a mean length of 200 nm. As a result, energy product of the wires reaches 44 MGOe. It is discovered that the morphology uniformity of the nanowires is the key to achieving the high coercivity and high energy density. Nanowires of this type are ideal building blocks for future bonded, consolidated and thin film magnets with high energy density and high thermal stability.

Engineered fabrication of ordered arrays of Au-NiO-Au nanowires

In the present paper, a novel method to fabricate ordered arrays of Au/NiO/Au nanowires is described, with the aim of filling the gap between the fundamental study of the electrical properties of scattered single nanowires and the engineered fabrication of nanowire arrays. This approach mainly consists of the following steps: (a) electrodeposition of Au/Ni/Au nanowires into an ordered porous anodic aluminum oxide template; (b) mechanical polishing of the sample to expose the gold tips of Au/Ni/Au nanowires to the template surface; (c) in situ annealing of the Au/Ni/Au nanowires without removing the template. The resulting structure consists in an ordered array of Au/NiO/Au nanowires slightly protruding out of a flat aluminum oxide template. Unlike current approaches, with the described method it is not necessary to remove the template in order to oxidize the middle metal, thus allowing the availability of an entire set of metal/oxide/metal nanowires ordered in a two-dimensional matrix and where single heterojunctions can be accessed individually.