The Dependence of Magnetic Properties on Diameters of One-Dimensional Nickel Nanostructures

Different Ni 1-D nanostructures were fabricated in various porous anodic alumina templates by electrodeposition, including Ni nanochains containing grains with diameters of 15 nm, Ni nanowires with diameters of 50 nm, and Ni nanotubes with outer diameters of 240 nm. The magnetic properties are strongly dependent on the morphology and size of Ni nanostructures. Ni nanochains have no obvious easy axis direction and present a very small coercivity. The easy axis of Ni nanowires is oriented parallel to the wire axis, and the effective magnetic anisotropy is mainly from shape anisotropy. For Ni nanotubes, easy axis is perpendicular to the tube axis, which is dominated by the magnetic dipole interaction. The angular dependence of the coercivity indicates that the weakly coupled nanoparticles within the Ni nanochains reverse their magnetization nearly independently, however, for Ni nanowires, magnetic reversal process is dominated by localized quasi-coherent nucleation mode, and Ni nanotubes show a complicated reversal behavior.