Nickel nanowire arrays with diameters in the range 30-500 nm have been fabricated by electrochemical deposition into nanoporous, single-crystal mica templates, which allow measurements of the magnetic properties of nickel nanowire arrays at high temperatures. The Curie temperature is found to be reduced by as much as 51 K for the 30 nm diameter nanowires. The Curie temperature shift with wire diameter follows the finite-size scaling relation with ϭ0.94 and 0 ϭ22 Å.The influence of reduced physical dimensions on magnetic entities is of both fundamental and technological interest. In bulk magnetic systems, the correlation length increases with temperature and diverges at the bulk transition temperature T C (ϱ). When one or more dimensions in the system are small, the growth of will eventually be limited by the smallest dimension d and the system displays a reduced transition temperature T C (d) due to finite-size effects. Technologically, as the feature sizes of magnetic structures continue to decrease, the influence of dimensionality on their magnetic properties has also become an important issue. To date, reports of finite-size effect in magnetic systems have been largely limited to ultrathin films and quasi-twodimensional systems. Measurements on quasi-onedimensional systems have been hampered by the difficulty in fabricating structures that are sufficiently small and stable over the required temperature range.In quasi-two-dimensional systems, thickness dependent phase transition temperatures have been measured in ultrathin ferromagnetic films of Ni, 1-6 Fe, 7,8 Co, 9 and Gd ͑Refs. 10-12͒ and CuMn spin glass films. 13,14 Recently, finite-size effects have also been reported in antiferromagnetic CoO ͑Refs. 15 and 16͒ and Cr ͑Ref. 17͒ thin films. In quasizero dimensional systems, such as granular thin films, phase transitions are not observed due to the onset of superparamagnetism when the particle size is very small. 18 Electrochemical deposition of metals into porous polymer films has been used to fabricate quasi-one-dimensional nanowire arrays 19-22 and the ferromagnetic properties of Ni and Co have been studied both at low temperatures and at room temperature. 22-25 However, measurements of magnetic phase transitions are not possible in these structures since the Curie temperatures for elements such as Ni, Co, and Fe are much higher than the temperature range of polymer templates. In this paper we describe the fabrication of quasi-onedimensional nickel nanowire arrays in porous mica films and show that this approach can be used to determine the temperature dependence of the magnetic properties at elevated temperatures.Nickel nanowire arrays were fabricated by electrochemical deposition into porous single-crystal muscovite mica templates. Mica is chemically stable up to 770 K, well above the Curie temperature for bulk Ni ͑ϳ630 K͒. The porous templates were fabricated by nuclear track etching. Particle tracks were formed in 5 m thick mica wafers by exposure to Ϸ6 meV ␣ particles from a 100 CiCf-252 source in a c...

Magnetite nanoclusters with an average size of about 120 nm have been prepared and allowed to self-assemble into one-dimensional (1D) nanochain structures with the average length about of 2 mum by a simple magnetic-field-induced (MFI) assembly approach (0.20 T). The constituent, phase, and morphology of these 1D nanochains have been characterized by X-ray diffraction and transmission electron microscopy. Magnetic measurement reveals that these 1D nanochains are weakly ferromagnetic at room temperature. In this paper, we discuss the influence of magnetization time and strength of external magnetic field on the formation of 1D nanochains. We also show that, by changing the amount of hydrogen peroxide in the starting materials, 1D nanochains with different interparticle spacing can be obtained. This 1D nanochain structure with different interparticle spacing would be an ideal system for the further study of magnetization properties of 1D ordered magnetic nanostructures.

One-dimensional wires of metallic nickel with width fluctuation were prepared in the presence of magnetic fields, and the chemical reduction of [Ni(N(2)H(4))(x)](2+) under magnetic fields was investigated.

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