Superparamagnetic and ferromagnetic Ni nanorod arrays fabricated on Si substrates using electroless deposition

Abstract

The microstructures and magnetic properties of nickel nanorods fabricated using an anodic alumina oxide template and electroless deposition were investigated. The as-deposited nanorods were found to contain nanocrystalline grains with an average size of approximately 2-3 nm. The temperature-dependent magnetic hysteresis curves indicated superparamagnetic behavior of the as-deposited rods as a result of the reduction of ferromagnetic crystallites. The superparamagnetic (SM) Ni nanorods transformed into ferromagnetic (FM) ones when annealed at 400 degrees C. Results from dark-field transmission electron microscopy reveal that the microstructure of the rods tends to form a laminar structure with grain growth parallel to the long axis of the rods, 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 to serve as magnetic building blocks in nanoscale devices, such as high-frequency inductors. On-chip magnetic spiral inductors were fabricated using these nanorods, and it was demonstrated that the nanorods can enhance inductance up to 6 GHz.

Competing magnetic interactions and interfacial frozen-spins in Ni-NiO core-shell nano-rods

“…16,17 The AAO was then removed, leaving the Ni rods to stand freely on Si. 18 The Ni/Si samples were post-annealed at 350 C for 15 and 30 min under atmospheric conditions to develop Ni-NiO core-shell structures with different NiO thicknesses. Meanwhile, two sets of Ni reference rods having the same dimensions as the Ni-NiO rods were prepared.…”

Magnetic properties of electroless-deposited Ni and Ni–NiO core–shell nano-arrays

“…Highly oriented Ni nano-arrays of diameter 70 nm and length 320 nm were fabricated directly onto Si substrates by electroless plating using an anodic aluminum oxide (AAO) template [12]. Prior to the electroless-deposition process, the AAO-Si sample was sensitized and activated by a SnCl 2 /HCl solution (40 g/L SnCl 2 þ3 ml/L HCl) and a PdCl 2 /HCl solution (0.15 g/L PdCl 2 þ 3 ml/L HCl).…”

“…On the other hand, the HRTEM demonstrated a polycrystalline structure for both the Ni-NiO and the reference Ni samples. Our previous work found that the as-deposited Ni featured a nano-crystalline structure [12], and a superparamagnetic (SM)-ferromagnetic phase transition of the arrays took place upon annealing. The conclusion was drawn that the magnetic transition is coupled to a microstructural modification that changes from nano-crystalline to polycrystalline phase [12].…”

“…Our previous work found that the as-deposited Ni featured a nano-crystalline structure [12], and a superparamagnetic (SM)-ferromagnetic phase transition of the arrays took place upon annealing. The conclusion was drawn that the magnetic transition is coupled to a microstructural modification that changes from nano-crystalline to polycrystalline phase [12]. This suggests that the microstructure can serve as an indicator of the magnetic ordering state and that a polycrystalline structure, regardless of its level of crystallinity, can be presumed to be in an FM state in accordance with the results shown in Figs.…”

Synthesis and magnetic properties of nickel nanoparticles deposited on the silicon nanowires

“…Previous studies focused on the ferromagnetic metals such as Fe, Co, and Ni had shown that the basic magnetic properties could vary significantly as a function of both size and shape, especially, when those nanoparticles were distributed to the substrate of high specific surface area [4][5][6][7][8][9][10]. In this condition, for nanoparticles, the thermal agitation would weaken the interaction forces; prevent the existence of stable magnetization and lead to the superparamagnetic (SPM) state [11][12][13].…”