Uniaxial magnetization performance of Co-Al2O3 nano-composite films electrochemically synthesized from acidic aqueous solution

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.

Uniaxial Magnetization Performance of Textured Fe Nanowire Arrays Electrodeposited by a Pulsed Potential Deposition Technique

Textured ferromagnetic Fe nanowire arrays were electrodeposited using a rectangular-pulsed potential deposition technique into anodized aluminum oxide nanochannels. During the electrodeposition of Fe nanowire arrays at a cathodic potential of - 1.2 V, the growth rate of the nanowires was ca. 200 nm s^-1. The aspect ratio of Fe nanowires with a diameter of 30 ± 5 nm reached ca. 2000. The long axis of Fe nanowires corresponded with the <200> direction when a large overpotential during the on-time pulse was applied, whereas it orientated to the <110> direction under the potentiostatic condition with a small overpotential. By shifting the on-time cathode potential up to - 1.8 V, the texture coefficient for the (200) plane, TC₂₀₀, reached up to 1.94. Perpendicular magnetization performance was observed in Fe nanowire arrays. With increasing TC₂₀₀, the squareness of Fe nanowire arrays increased up to 0.95 with the coercivity maintained at 1.4 kOe at room temperature. This research result has opened a novel possibility of Fe nanowire arrays that can be applied for a new permanent magnetic material without rare-earth metals.