Superparamagnetic and ferromagnetic Ni nanorod arrays fabricated on Si substrates usingelectroless deposition

Abstract

The microstructures and magnetic properties of nickel nanorods fabricated using an anodicalumina oxide template and electroless deposition were investigated. The as-depositednanorods were found to contain nanocrystalline grains with an average size of∼2–3 nm. The temperature-dependent magnetic hysteresis curves indicated superparamagneticbehavior of the as-deposited rods as a result of the reduction of ferromagnetic crystallites. Thesuperparamagnetic (SM) Ni nanorods transformed into ferromagnetic (FM) ones when annealed at400 °C. Results from dark-field transmission electron microscopy reveal that the microstructure ofthe rods tends to form a laminar structure with grain growth parallel to the long axis of therods, together with the enhancement of ferromagnetic ordering along the same direction.The results suggest that the SM–FM phase transition obtained is microstructure driven.The Ni nanorods manufactured by the electroless deposition also have the potential toserve as magnetic building blocks in nanoscale devices, such as high-frequency inductors.On-chip magnetic spiral inductors were fabricated using these nanorods, andit was demonstrated that the nanorods can enhance inductance up to 6 GHz.