Evidence for strong magnetoelastic effects in Ni nanowires embedded in polycarbonate membranes

The uniaxial anisotropy energy of arrays of submicronic (30-500 hm) Ni wires synthesized by electrodeposition into cylindrical pores of track-etched polycarbonate membranes is studied as a function of temperature. At room temperature, the uniaxial anisotropy is equal to the shape anisotropy whereas an additional contribution, that reinforces the wire axis as an easy axis is evidenced at low temperature. This additional contribution is demonstrated to find its origin in magnetoelastic effects conjointly induced by the Ni and polycarbonate thermal-expansion coefficients mismatch and by the low volume fraction of Ni in Ni/polycarbonate samples

Arrays of nanowires of magnetic metals and multilayers: Perpendicular GMR and magnetic properties

The template strategy combined with electrodeposition techniques have been used to fabricate arrays of nanowires of magnetic metals and multilayers in the cylindrical pores of track-etched polymer membranes, The giant magnetoresistance effects have been investigated in two different types of multilayered nanowires systems: Co/Cu and Ni80Fe20/Cu. In addition, a comparative study of the magnetic properties of sub-micron Ni, Co, Fe and Ni80Fe20 wires is made by means of anisotropic magnetoresistance and magnetization experiments

Fabrication and properties of arrays of superconducting nanowires

We report on the fabrication and structural characterization of arrays of superconducting nanowires by electroplating lead into the nanopores of track-etched polymer membranes. The diameters of the lead nanowires range from 400 down to 70 nm, whereas their length is about 20 mu m. Large enhancement of the critical field has been observed in good agreement with the Ginsburg-Landau-Silin theory. By comparing the predicted critical field enhancement for thin cylinders with experimental results, we have extracted the effective penetration depth. The dependence of the effective penetration depth and electron mean free path on the wire diameter is also discussed

Preparation and characterization of electrodeposited Fe and Fe/Cu nanowires

Fe and Fe/Cu multilayered nanowires with layer thicknesses in the 10nm range were successfully synthesized within the voids of nanoporous polycarbonate membranes and characterized by transmission electron microscopy. Magnetization measurements show that the shape anisotropy of individual Fe wires dominates the magnetic properties. Fe(8nm)/Cu(10nm) multilayered nanowires show CPP-GMR ratios as large as 12% at low temperature. The variations of the CPP-GMR as a function of the Cu layer thickness are consistent with the Valet-Fert model. Our data yield a value of about 0.3 for the bulk spin asymmetry coefficient beta

Perpendicular giant magnetoresistance of NiFe/Cu multilayered nanowires

We have prepared by electrodeposition Ni80Fe20/Cu multilayered nanowires into the pores of polymer membranes and performed giant magnetoresistance (GMR) measurements in the current perpendicular to the layer planes geometry. GMR ratios as high as 80% have been obtained at 4.2 K. Two types of structure have been studied: conventional Ni80Fe20/Cu multilayers and multilayers composed of Ni80Fe20/Cu/Ni80Fe20 trilayers magnetically isolated by long Cu rods. (C) 1997 American Institute of Physics

Magnetoresistance of a single domain wall in Co and Ni nanowires

We report on the domain wall magnetoresistance of Co and Ni nanowires of 45 nm on diameter or less. The enhancement of the resistance due to an isolated domain wall is clearly evidenced from magnetoresistance hysteresis loops obtained under parallel and perpendicular fields. The domain walls magnetoresistance effect is by one order of magnitude smaller in Ni than in Co and it was observed only at low temperature for Ni nanowires, The formation and motion of domain walls is demonstrated by MFM experiments

Evidence for a short spin diffusion length in permalloy from the giant magnetoresistance of multilayered nanowires

We present magnetization and giant magnetoresistance (GMR) measurements performed on two series of electrodeposited Py/Cu multilayered nanowires (Py = Ni80Fe20) of diameter null set =90 nm. The multilayers of the first series are composed of a conventional stacking of Py and Cu layers and the GMR is studied as a function of the Cu thickness for a constant Py thickness. The multilayers of the second series are composed of Py/Cu/Py trilayers uniformly distributed along the filament and separated from each other by thick Cu layers. For this second series, magnetic and GMR properties were investigated as a function of the Py layer thickness and our magnetization measurements demonstrate that, for Py layers thinner than about 90 nm, the magnetic moments of the two Py layers of a trilayer are approximately antiparallel at zero field. Analysis of the GMR data using the Valet-Fert model allows us to estimate that the spin diffusion length in Py, L-sf((PY)) , is between 3.3 and 5.3 nm. [S0163-1829(99)06125-1]

Fabrication and properties of organic and metal nanocylinders in nanoporous membranes

Chemical and electrochemical techniques were used for generating ensembles of randomly distributed organic and metal nanocylinders into the pores of nuclear track-etched polycarbonate membranes. This so-called "template method" makes it possible to synthesize a variety of materials including metals, ferromagnets, superconductors, semimetals, and conducting polymer and structures such as solid wires, tubules, composite nanostructures, and multilayers. Numerous interesting properties have been identified in relation to the nanoscopic dimensions of the materials

Transport and vibrational properties of poly(3,4-ethylenedioxythiophene) nanofibers

Nanofibers of poly(3,4-ethylenedioxythiophene) (PEDOT) have been electrochemically synthesized by the template method and their morphology determined using electron microscopy. A comparative resonant Raman scattering study has been performed on films, bundles of fibers and individual fibers of different diameters. Their temperature dependent transport properties have also been investigated and compared with the case of a PEDOT thin film. The PEDOT is found to be in an insulating state close to the metal-insulator transition. The temperature dependence of the fibers' conductance is larger than for the films, and this variation increases for a smaller fiber diameter. These results suggest that a confining effect on the PEDOT structure occurs during the electrochemical synthesis in the template. (C) 2002 Elsevier Science B.V. All rights reserved