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We address the statistical patterning of nanoscale lattices and discuss the probability to overlap a finite number of lattice features with a given entity. The experimental exemplification is done through selective nanowire growth using nanoporous alumina templates. This random patterning approach is found to provide rigorous selection rules for locating definite sets of objects into nanoporous templates. Remarkably, no alignment with respect to the template's features is required to achieve single-nanopore resolution with probabilities as high as 92% upon properly choosing the size of the processing mask. The approach is found to be scale-invariant with a minimal influence of the masking item symmetry and with good reliability of the mask-to-nanopore overlapping threshold. Routed in surface optimization, this study dives into the discrete geometry of quasi-periodic lattices through simple technological processing and analytical approaches.

The ferromagnetic resonance properties in arrays of low diameter bistable nanowires have been studied. Measurements performed in the frequency swept mode show that in nonsaturated states, wires magnetized in the positive and negative direction absorb at different frequencies giving place to spectra with two absorption peaks. Moreover, the positive and negative wires obey different dispersion relations, which allow interpreting their different frequency-field dependence in terms of the uniform precession mode. Measurements along sets of first-order reversal curves allow to determine the dipolar interaction field as a function of the magnetic state. The configuration dependence of the interaction field is found to be proportional to the value of the dipolar interaction field of the saturated state. An analytical mean-field expression, which explicitly incorporates the dependence of the interaction field with the magnetic configuration, is proposed and used to obtain a general expression for both the effective field and the dispersion relation, which describes with remarkable agreement the ferromagnetic resonance measurements in saturated and nonsaturated states.

International audience; Unbiased planar microwave circulators were fabricated by electrodeposition of NiFe nanowires into porous alumina templates. Microwave properties of the devices are seen to depend drastically on the height of the nanowires and the newly developed devices exhibit improved features, compared to existing nanowire-based designs. Thanks to the high anisotropy of the nanowires, zero-field circulation modes may be observed in a frequency range from 10 to 30 GHz, with isolation as large as 30 dB, as well as low insertion losses - 5 dB, making it compatible with industrial needs for device applications.

We report measurements of the temperature dependence of the resistivity in zero magnetic field and in magnetic fields up to 5 tesla for weakly disordered fluorine-intercalated graphite fibers (CxF) with various fluorine concentrations (3.6 < x < 5.8). These results have been used to determine the importance of weak localization and carrier-carrier interaction in these two-dimensional (2D) systems. We found that both quantum phenomena contribute to the logarithmic increase of resistivity with decreasing temperature, though the interaction effect is generally dominant. Also, the magnitude of the resistivity increase is very sensitive to the fluorine concentration. The temperature dependence of the inelastic scattering rate 1/tau(i), as obtained from magnetoresistance measurements, is well fitted by a polynomial expression of the form tau(i)-1=alpha-T+beta-T2. The linear term tau(i)-1(T) exhibits a good quantitative agreement with the theoretical prediction for the expected disorder dependence of the carrier-carrier scattering in 2D disordered metals.

Disorder-induced phenomena are evidenced in both electrical and thermal transport properties of various graphite host materials with transition metal fluoride (C/sub x/MF/sub y/ with M=Cr, Rh, Au and Ir). The electrical resistivity results are analyzed in the framework of weak-localization and carrier-carrier interaction models for two-dimensional disordered electron systems. Compared to other acceptor compounds, these fluoride GICs exhibit essentially two new features. First, for some highly resistive compounds, the logarithmic increase in resistivity with decreasing temperature starts already at room temperature and is dominant down to the lowest temperature investigated (1.5 K). Second, the effect of disorder is also observable in the temperature dependence of the thermal conductivity and thermoelectric power.

We report and discuss experimental data on the thermoelectric power of magnetic multilayers. Measurements of the thermoelectric power of Fe/Cr, Co/Cu and Fe/Cu multilayers have been carried out in the temperature range 4 K < T < 150 K magnetic fields perpendicular to the layers. All specimens were found to exhibit pronounced magnetothermoelectric power (MTEP) effects correlating with their giant negative magnetoresistance. The main difference between the MTEP and the magnetoresistance is in their temperature dependence. Whereas the magnetoresistance is a decreasing function of temperature, the MTEP, at least in Co/Cu and Fe/Cu multilayers, is very small at low temperature and increases rapidly above 30-40 K. We ascribe this high temperature part of the MTEP to spin-dependent electron-magnon scattering and we propose a theoretical model.

The intercalation process of some d-transition metal fluorides in graphite has been investigated using anhydrous liquid HF. C(x)MF(y) GICs have been obtained for M = Cr, Rh, Ir and Au. The charge transfer has been evaluated from optical reflectivity measurements. Comparison has been carried out between electrical conductivity obtained from optical data and from a contactless method. Results on the in-plane electrical resistivity and thermal conductivity are reported. All compounds exhibit a logarithmic resistivity divergence in the low-temperature range due to weak localization and carrier-carrier interaction effects for 2D metals.

We report on the domain wall magnetoresistance of Co and Ni nanowires of 35 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.

We report on the microwave properties of a nanostructured magnetic planar substrate. It consists of an array of parallel magnetic nanowires constituted of nickel, cobalt or Ni/Fe alloy embedded in a porous polymer membrane. Experiments consist of transmission measurements carried out on microwave stripline. Measurements were performed at frequencies ranging from 100 MHz to 40 GHz and under static magnetic fields up to 5.6 kOe applied along the wire axis. Resonance phenomena have been observed in the presence but also in the absence of the DC magnetic field at frequencies which depend on the nature of the material and the applied static magnetic field. Results are consistent with those expected for a ferromagnetic resonance (FMR) experiment and the observed behaviors are analyzed in the framework of the classical FMR theory.

Applying current in type-II superconducting sub-micron size structures often leads to a discontinuity of the current-voltage characteristic as the instability current is reached. Also voltage-bias mode allows to avoid such an abrupt switch to the normal state, and gives a relevant outlook of the involved resistive phenomenons. Current and voltage-bias measurements on NbN microbridges with a constriction are reported here as a function of temperature and transverse magnetic field. Starting from a 75nm-thick sputtered film, 160nm-wide microstrips were patterned with an half-wide section constriction in their middle. From the current-bias curves it appears that the discontinuities are due to a flux flow instability that rapidly evolves in a hot-spot. Moreover applying the voltage reveals several dissipative states that leads to successive S-shaped current oscillations in a small current range. Formation of vortex channels can be considered to explain these features.

Dense arrays of ordered ferromagnetic nanowires have been used to create periodic magnetic pinning centers in thin superconducting NbN films. The nanowires were electrodeposited in a highly ordered porous alumina membrane and the thin NbN film was deposited on top of the perpendicularly oriented magnetic nanowires. Matching effects have been observed up to 2.5 T (11th matching field) and are maintained at low temperature. An appreciable enhancement of the superconducting properties is observed. At low fields, a hysteretic behavior in the magnetoresistance is found, directly related to the magnetization processes of arrays of interacting single domain ferromagnetic nanowires. (C) 2009 American Institute of Physics. [doi:10.1063/1.3276557]

We present magnetotransport measurements as well as micromagnetic simulations of magnetization reversal in magnetic nanowires having strong transverse magnetocrystalline anisotropy. The interplay between exchange, demagnetizing, and magnetocrystalline energies gives rise to a micromagnetic configuration involving vortices with alternative chirality along the wire. Despite the complexity of the field angle-dependent magnetization reversal process, a very good agreement is obtained between experiments and simulations. This provides evidence that the reported magnetization process appears generally in nanowires with strong transverse magnetocrystalline anisotropy. Moreover an analytical expression is established for the angular dependency of the core switching field. The simulations indicate the occurrence of Bloch points during the core reversal.

Microwave devices demand nowadays small sizes and broad bandwidth. Ferromagnetic nanowired membranes are ideal candidates for this purpose. Planar, tunable and nonreciprocal devices can be designed with them. Therefore we propose an isolator concept based on such a material. Its principle is based on a nonreciprocal microstrip line. Anglais

The interest in the template-based synthesis of nanomaterials and nanostructures is continuously increasing due to the advantageous features offered by the templates and the ease of processing a large number of nanostructures in parallel. In recent years, nanoporous anodic aluminum oxide (AAO) has been intensively studied and used for that purpose. [1] At present, it is considered one of the most promising templates [2] mainly because of its unique features, which include easily tunable geometrical parameters, mild preparation conditions, and resistance to high temperatures. AAO, whichisatypicalself-orderednanopore-arraymaterialformed by the electrochemical oxidation of Al in acidic solutions, is an excellent starting host material for the fabrication of various nanomaterials and nanostructures. It possesses a hexagonally packed arrangement of nanoscale-sized straight blind holes aligned perpendicular to the surface. The voids of the nanoscale-channeled structure are typically filled with various materials and heterostructures using electrochemical or chemical vapor deposition methods after the elimination of the oxide barrier layer that closes the bottom ends of the holes. While this barrier layer is typically considered undesirable and eliminated, herein we emphasize that the surface of this layer possesses an ordered array of hemispheres that can also be used as a very interesting template. We describe the advantages of the ordered bumpy surface for creating artificial superconducting pinning centers in Nb films deposited on it.

Results on the temperature and magnetic field dependence of the Hall effect in pregraphitic pyrocarbons heat treated between 1700 degrees C and 2200 degrees C are presented. The experimental data are discussed in terms of the two-carrier-minority and majority holes-model. It is shown that this model is able to reproduce all the set of experimental data in the low temperature range. Best fit calculations clearly show that minority carriers play a significant role, especially at low temperature. The temperature dependence of the low field Hall coefficient: R/sub H0/ originates from that of the minority holes mobility, while the field dependence of R/sub H/ is due to the high mobility of those carriers. Hall effect measurements appear to be well suited for investigating properties of high mobility minority carriers in disordered graphite.

The transport properties of isotropic pitch-based carbon fibers with surface area 1000 m2/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity, and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons.

Preliminary results on the effect of stretching on the thermal conductivity of polyacetylene films are presented. Also, data on the in-plane anisotropy and on the effect of of FeCl3 content will be discussed.

Nous avons mesure la conductivite electrique et la conductivite thermique dans la direction des feuillets de composes d’insertion du graphite de premier stade inseres aux especes magnetiques CoCl2 et FeCl3 . Pour chaque propriete, on observe une anomalie aux alentours de la temperature de transition de phase magnetique. Pour la conductivite thermique, nous attribuons cette anomalie a une contribution des magnons, en accord avec d’autres etudes de proprietes physiques realisees sur de tels composes. En ce qui concerne la conductivite electrique, les composes d’insertion graphite-CoCl2 et graphite-FeCl3 presentent un comportement different.

We report on the microwave properties of arrays of parallel magnetic nanowires constituted of nickel, cobalt, or Ni/Fe alloy embedded in nanoporous track-etched polymer membranes. The experiments consist of transmission measurements carried out on microwave stripline structures using a magnetically loaded membrane as the substrate. Measurements were performed at frequencies ranging from 100 MHz to 40 GHz and under static magnetic fields up to 5.6 kOe applied along the wires axis. Resonance phenomena have been observed in the magnitude of the complex transmission coefficient at frequencies which depend on the nature of the material and applied static magnetic field. Results are consistent with those expected for a ferromagnetic resonance (FMR) experiment and the observed behaviors are analyzed in the framework of the classical FMR theory. (C) 1999 American Institute of Physics. [S0003-6951(99)02338-4].

Arrays of electrodeposited CoCu/Cu multilayered nanowires have been characterized by ferromagnetic resonance and magnetometry measurements in order to study the effect of the dipolar interactions on the effective anisotropy field as a function of the magnetic and nonmagnetic layer thicknesses. Breaking the continuous cylinder geometry results in a reduction of the effective anisotropy field, which can be modified over a large range of values starting from 7 kOe in the case of nonlayered continuous nanowires down to nearly zero for the thinnest magnetic layers. An analytical model is presented to describe the magnetostatic interactions between magnetic layers and their effect on the total anisotropy field which shows a very good agreement with the experiments. Moreover, the model allows generalizing the description of the effective magnetostatic field as a function of the aspect ratio of both the magnetic and the nonmagnetic layers for multilayered nanowires of any combination of materials. A general anisotropy diagram is presented that describes the geometrical conditions required to obtain an easy axis parallel or perpendicular to the wire axis, thus providing a guide for the engineering and fine-tuning of the magnetic properties of these systems.

Transport properties of a superconducting NbN nanowire are studied experimentally and theoretically. Different attached leads (superconducting contacts) allowed us to measure current-voltage (I-V) characteristics of different segments of the wire independently. The experimental results show that with increasing the length of the segment the number of jumps in the I-V curve increases indicating an increasing number of phase-slip phenomena. The system shows a clear hysteresis in the direction of the current sweep, the size of which depends on the length of the superconducting segment. The interpretation of the experimental results is supported by theoretical simulations that are based on the time-dependent Ginzburg-Landau theory, the heat equation has been included in the Ginzbur-Landau theory.

Arrays of nickel nanowires embedded into polycarbonate membranes were studied by means of ferromagnetic resonance. Large magnetoelastic effects were evidenced in the entire temperature range 4.3-300 K, which were attributed to the thermal expansion coefficients mismatch between the Ni nanowires and the polycarbonate membrane. The resulting magnetoelastic energy was measured as a function of both membrane porosity and diameter of the nanowires. For low volume fractions of Ni in Ni/polycarbonate samples, the magnitude of the magnetoelastic anisotropy may be as high as the shape anisotropy. Conversely, no magnetoelastic effects were observed in permalloy nanowires embedded in the same membranes.

We report measurements on the electrical- and thermal-transport properties of fluorine-intercalated vapor-grown carbon fibers ${\mathrm{C}}_{\mathit{x}}$F with the carbon-to-fluorine-atom ratio x between 4.1 and 5.8. The electrical resistivity is found to be very sensitive to the fluorine concentration. Indeed, while the resistivities of the ${\mathrm{C}}_{5.2}$F and the ${\mathrm{C}}_{5.8}$F compounds are well below that of the pristine graphite fibers, the tendency is reversed when x\ensuremath{\le}4.5 and large resistivity values are obtained. All ${\mathrm{C}}_{\mathit{x}}$F compounds exhibit a logarithmic resistance increase at low temperature, which can consistently be explained by weak-localization and carrier-carrier interaction effects for two-dimensional electron systems. Large negative magnetoresistance values have been measured on the ${\mathrm{C}}_{\mathit{x}}$F compound with x=4.1. At higher temperature, an anomalous resistance-versus-temperature behavior appears for each fluorine-intercalated vapor-grown carbon fiber, possibly resulting from a phase transition. Heat transport in ${\mathrm{C}}_{\mathit{x}}$F (with x=4.1) is almost entirely governed by lattice vibrations between 2.5 and 300 K while the thermoelectric power is positive, and its temperature dependence is similar to that previously observed in other acceptor graphite intercalation compounds. Our results indicate that the high resistivity of the ${\mathrm{C}}_{\mathit{x}}$F compounds (with x\ensuremath{\le}4.5) is due to strong defect scattering rather than a low free-charge-carrier density.

We report an experimental study of guided transmission of low-energy (200-350 eV) electrons through highly ordered Al2O3 nanocapillaries with large aspect ratio (140 nm diameter and 15 mu m length). The nanochannel array was prepared using self-ordering phenomena during a two-step anodization process of a high-purity aluminum foil. The experimental results clearly show the existence of the guiding effect, as found for highly charged ions. The guiding of the electron beam was observed for tilt angles up to 12 degrees. As seen for highly charged ions, the guiding efficiency increases with decreasing electron incident energy. The transmission efficiency appeared to be significantly lower than observed for highly charged ions and, moreover, the intensity of transmitted electrons significantly decreases with decreasing impact energy.

Microwave devices as filters or couplers demand nowadays small sizes and broad bandwidth. Because of their unusual characteristics, left-handed materials are an ideal candidate for this demand. This paper proposes a new concept for left- handed materials based on ferromagnetic nanowired substrates, which provides at the same time a planar and tunable solution. The concept is based on an accurate model for the permeability of the nanowired substrate.

Specific heat (C) measurements have been performed on several compositions of the U-2(Ru1-xRhx)(3)Si-5 system showing an interesting magnetic phase diagram: (i) no magnetic ordering appears above 2 K for 0 less than or equal to x antiferromagnetic transition), a very strong enhancement of CIT is observed below 12 K, reaching a value as high as 255 mJ/U-mol K-2 at 2 K. This behaviour suggests either the occurrence of magnetic ordering below 2 K or that this silicide can be considered as the heaviest electron system. (C) 1998 Elsevier Science S.A.

Using appropriate electrodeposition conditions, it is shown that the structural and magnetic properties of arrays of Co and CoCu/Co nanowires can be controlled. The hcp c axis orientation can be oriented parallel or perpendicular to the wire axis simply by changing the pH of the electrolytic solution and/or deposition rate. This selected orientation of the c axis leads to a drastic change in overall magnetic anisotropy and is promising for the fabrication of spin valves structures by electrodeposition.

We performed photoluminescence experiments on colloidal, Co2+-doped ZnO nanocrystals in order to study the electronic properties of Co2+ in a ZnO host. Room temperature measurements showed, next to the ZnO exciton and trap emission, an additional emission related to the Co2+ dopant. The spectral position and width of this emission does not depend on particle size or Co2+ concentration. At 8 K, a series of ZnO bulk phonon replicas appear on the Co2+-emission band. We conclude that Co2+ ions are strongly localized in the ZnO host, making the formation of a Co2+ d-band unlikely. Magnetic measurements revealed a paramagnetic behaviour. (c) 2005 Elsevier B.V. All rights reserved.

We have investigated the magnetization reversal processes in arrays of sub-micron Ni and Co wires by means of magnetization and torque experiments together with micromagnetic calculations. The wires were produced by electrodeposition in the cylindrical pores of track-etched polymer membranes. Diameters in the range 35–400 nm have been studied. The arrays of Co and Ni nanowires display different magnetic behaviors. Particular emphasis is given to the competing shape and crystal magnetic anisotropies that exist in the Co nanowire system. In both systems, explaining the experimental results requires domain formation, except for the smallest diameters where single domain behavior occurs.

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.

A convenient way of controlling the magnetic anisotropy of electrodeposited cobalt nanowires was studied. The nanowires were grown by electrodeposition into the cylindrical pores of a polycarbonate membrane. Using ferromagnetic resonance and transmission electron microscopy, it was demonstrated that changes in the two main electrodeposition parameters (electrolyte pH and deposition rate/current density) leads to modifications of the crystallographic structure of the nanowires that can be grown in cubic (FCC) or hexagonal (HCP) phases.

Experimental results on the phase slip process in superconducting lead nanowires are presented under two different experimental conditions: constant applied current or constant voltage. Based on these experiments we established a simple model which gives us the condition of the appearance of phase slip centers in a quasi-one-dimensional wire. It turns out that the competition between two relaxations times (relaxation time of the absolute value of the order parameter $\tau_{|\psi|}$ and relaxation time of the phase of the order parameter in the phase slip center $\tau_{\phi}$) governs the phase slip process. Phase slip phenomena, as periodic oscillations in time of the order parameter, is possible only if the gradient of the phase grows faster than the value of the order parameter in the phase slip center, or equivalently if $\tau_{\phi}, Comment: 13 pages, 15 figures

The nuclear contribution to the specific heat of thulium has been investigated in the temperature range 0.02--0.6 K and in the presence of a magnetic field. The data can be well fitted to C=\ensuremath{\gamma}T+\ensuremath{\alpha}${\mathit{T}}^{3}$+${\mathit{C}}_{\mathit{N}}$, where the first two terms represent the electronic and the lattice contribution, respectively, and ${\mathit{C}}_{\mathit{N}}$ is the nuclear specific heat. Using a two-level Schottky model for ${\mathit{C}}_{\mathit{N}}$, a ground-state energy splitting of 8.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ eV and a degeneracy ratio of 1.28 were calculated. Consistent with the estimated very large effective magnetic field (565 T), an external magnetic field up to 14 T was found to have no significant effect on ${\mathit{C}}_{\mathit{N}}$.

Summary form only given. Ferromagnetic resonance (FMR) in electrodeposited ferromagnetic nanowires is studied up to 40 GHz using a micro-strip transmission line. Due to the simple geometry of these systems, the FMR can be described very simply when there is no anisotropy contribution other than the shape anisotropy. Tunability of the resonance frequency and the effective resonance frequency range are determined by the shape anisotropy and hence the saturation magnetization M/sub S/.

Applying a constant voltage to superconducting nanowires we find that its IV-characteristic exhibits an unusual S-behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j_{c2} at which the pure superconducting state becomes unstable and j_{c1}, Comment: 4 pages, 5 figures, replaced with minor changes

We present a statistical analysis of the magnetization processes in arrays of 22-mum-long, 40-nm-wide Co and Ni nanowires, with parallel-to-wire magnetic anisotropy, electrodeposited into porous polycarbonate membranes. This analysis is based on usual magnetization measurements taken with a magnetic field applied parallel to the average wire direction. It is shown that the magnetization curves may contain, in proportions which depend on the magnetic history of the arrays prior to the measurement, two contributions corresponding, respectively, to single-domain wires reversing their magnetization and to wires initially in a multidomain state which are remagnetized to saturation. Despite the extremely large number of wires involved, these two contributions exhibit clearly discernible substructures. These are related to the different and rather weakly distributed characteristic fields that describe the reversal and remagnetization processes: the nucleation and propagation fields. Numerical simulations of the magnetization curves are carried out which allow one to deduce the statistical distributions of these fields. From this modeling of the experimental data, it is shown that two distinct kinds of defects with very different pinning strength are certainly present in the nanowires. Finally, the analysis of the magnetization curves also provides accurate information concerning the distribution of wire orientation in the polycarbonate templates.

The zero-field microwave absorption, or natural ferromagnetic resonance, spectra in arrays of electrodeposited magnetic nanowires is studied as a function of the saturation magnetization of NiCu, NiFe, CoNiFe, and CoFe alloys of several compositions. Measurements show that due to the shape anisotropy, these systems present strong absorption peaks in the absence of an applied magnetic field in the GHz range due to the ferromagnetic resonance. Furthermore, the zero-field resonance frequency is observed to be independent of the wire diameter and density as well as the magnetic history and its value depends only on the material, through the saturation magnetization and the gyromagnetic factor. It is shown that, using different electrolytic solutions and depositing at different electrostatic potentials, the alloy composition can be varied and the remanent state resonance frequency can be tailored quasicontinuously between 4 and 31 GHz. (C) 2002 American Institute of Physics.

We demonstrate the operation of a fully integrated and miniaturized waveguide based on ferromagnetic nanowires as a promising alternative to macroscopic ferrite slab-loaded metallic rectangular waveguides used as microwave isolators. Nanowires of various heights are selectively grown at dedicated areas into a low-loss nanoporous alumina template in order to create the shielding walls of a Substrate Integrated Waveguide (SIW) topology and the ferromagnetic slab supporting a circularly polarized nonreciprocal propagation. A model is proposed for the microwave response of the SIW and its non-reciprocity, which takes into account the substrate permittivity and the tensorial permeability of the ferromagnetic nanowires, and its predictions are validated by measurements. A significant isolation of 7 dB/cm is obtained experimentally at 13.5 GHz, without the need of a DC bias magnetic field.

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements., Comment: 7 pages, 5 figures

Using ferromagnetic resonance, the angular dependence of the uniform precession mode of infinite cylinders is investigated at room temperature for low density Ni nanowire arrays, embedded in a polycarbonate membrane, with wire diameters ranging from 35 mn to 500 nm. All wires reveal a very similar behavior of the resonance field vs angle, independent of the wire diameter and wire density, corresponding to the uniform precession mode of an infinite cylinder including the shape demagnetization anisotropy and a small uniaxial anisotropy contribution. From the analysis of the angular dependence of the linewidth, the distribution of the wire orientation and the effective anisotropy field can be estimated. The latter is broadened due to the presence of a sub-structure in the absorption spectra.

Using a planar microstrip transmission line, the dipolar interactions in electrodeposited Ni nanowires arrays an characterized as a function of the membrane porosity (4% to 38%) and the wire diameter (56 to 250 nm). The dipolar interactions between the wires can be modeled in a mean-field approach as an effective uniaxial anisotropy field oriented perpendicular to the wire axis and proportional to the membrane porosity. The dipolar interaction field opposes the self-demagnetization field of an isolated single wire which keeps the magnetization parallel to the wire axis. An increase in the porosity therefore induces a switching of the effective anisotropy easy axis from parallel to perpendicular to the win axis above a critical porosity of 35-38% independent of the wire diameter.

Arrays of Cu/Cu 2 O nanowires are electrodeposited at room temperature from alkaline solutions of copper lactate in the nanopores of track-etched polymer membranes. Using the appropriate solution, the electrode potential spontaneously oscillates during the application of a constant cathodic current. Both the period of the oscillations and the composition of the nanowires can be controlled by varying the applied current density. A nanocomposite of copper and cuprous oxide is deposited at an applied current over which oscillations occur. In contrast, pure Cu or Cu 2O nanowires are obtained at deposition current out of the range of oscillation.

This paper investigates for the first time the microwave properties of arrays of magnetic nanowires embedded into a planar substrate. Our experiments show that the structure acts like an equivalent microwave ferrite substrate having several advantages. Resonances are indeed obtained in the measured transmission term of a microstrip transmission line deposited on the equivalent substrate. Those resonances are tunable according to a DC magnetic field applied to the structure. Observed results agree very well with the ferromagnetic resonance. Those observations open the road to a new generation of planar ferrite devices.

We have fabricated Pb, Sn and multilayered Pb/Cu nanowires using electrodeposition in nanoporous template. Single wires 50 nm in diameter and 20 mu m long are contacted with either An or Pb (superconducting) films using a self-contacting technique. We have measured Pb and Sn wires with Pb contacts and careful filtering. The proximity effect is probe in this geometry with the Sn nanowire that becomes superconducting near the Pb critical temperature due to the Pb contacting layers. (c) 2007 Elsevier B.V. All rights reserved.

The dipolar interaction field in arrays of nickel nanotubes has been investigated on the basis of expressions derived from the effective demagnetizing field of the assembly as well as magnetometry measurements. The model incorporates explicitly the wall thickness and aspect ratio, as well as the spatial order of the nanotubes. The model and experiment show that the interaction field in nanotubes is smaller than that in solid nanowires due to the packing fraction reduction in tubes related to their inner cavity. Finally, good agreement between the model and experiment is found for the variation of the interaction field as a function of the tube wall thickness.