Ni microparticles in nonmagnetic elastic matrices have a magnetic behavior which depends on particles percentage, temperature, intensity of magnetizing field and the induced strain. In particular, the elastic properties of the matrix give nonconventional effects of deformation on magnetization. When a compression is applied and the magnetizing field is high, i.e., near saturation, it becomes evident the importance of magnetic particles density increment. On the other hand, if the magnetizing field is little, below 1/4 of saturation field, the effect of elastic matrix deformation on particles' orientation and the consequent change of the magnetization intensity is prominent. We named the last peculiar behavior as "elastomagnetic" effect and a simple model to explain it is reported. A threshold field as a function of the particles concentration is experimentally determined which gives the prominence of one or the other of the above described mechanisms. The experimental results and the theoretical model explain that even when the intrinsic magnetoelastic effect is negligible one can find magnetoelastic effects due to coexistence of phases with different geometry, elastic and/or magnetic properties

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research communities due to their good electrical conductivity, high stiffness and high strength at relatively low CNT contents. Effective utilization of CNT in composites depends primarily on the ability to disperse them homogeneously throughout the polymer matrix, avoiding the formation of bundles due to van der Waals interactions existing between the nanotubes. In this work composites of polystyrene at various percentages of SWNT were fabricated using Latex Technology technique, a polymer type‐independent method based on using a surfactant as a dispersing agent. An electrical characterization of SWNT composites was performed both in DC and AC modes. From the analysis of DC data a percolative behavior was found for the conductivity as function of SWNT content. The innovative contribution of this work consists in the modeling of the composite material upon its electrical properties. AC measurements and the analysis of impedance as function of angular frequency lead to the formulation of an equivalent circuit able to model the composite material in correspondence of the percolative threshold.

We present experimental results concerning both the fabrication and characterization of superconducting tunnel junctions containing superconductor/ferromagnet ͑S/F͒ bilayers made by niobium ͑S͒ and a weak ferromagnetic Ni 0.50 Cu 0.50 alloy. Josephson junctions have been characterized down to T = 1.4 K in terms of current-voltage I-V characteristics and Josephson critical current versus magnetic field. By means of a numerical deconvolution of the I-V data the electronic density of states on both sides of the S/F bilayer has been evaluated at low temperatures. Results have been compared with theoretical predictions from a proximity model for S/F bilayers in the dirty limit in the framework of Usadel equations for the S and F layers, respectively. The main physical parameters characterizing the proximity effect in the Nb/ NiCu bilayer, such as the coherence length and the exchange field energy of the F metal, and the S/F interface parameters have been also estimated.

Articles you may be interested inEffect of superconducting spacer layer thickness on magneto-transport and magnetic properties of La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 heterostructures

The authors have performed experiments on current-induced domain wall (DW) displacement in La0.7Sr0.3MnO3 nanostructures patterned by gallium (Ga) focused-ion-beam milling. A dc current is found to assist or hinder, according to polarity, an external magnetic field in the depinning of a DW trapped in a nanoconstriction. For large enough currents, the DW depinning occurs in the absence of external magnetic field. The depinning current depends on the transverse anisotropy constant of the region toward which the DW is displaced

International audienceWe present here recent results on detection of surface and subsurface artificial features in Al-Ti planar structures, to show current performance of our eddy-current nondestructive evaluation system based on HTc SQUIDs. The anomalous magnetic fields generated by flaws with known electromagnetic characteristics have been modeled by three-dimensional codes based on finite element method and volume integral formulation and developed for the investigated problem. Both numerical solutions have correctly predicted the shape of the complicated magnetic field response which is mainly the result of the shape of the defect, the geometry of the inducing coil and the characteristics of the SQUID gradiometer

Polymer-embedding of nano-sized indium tin oxide (SnO center dot In2O3, ITO) produces electrically conductive materials transparent to the visible light at filling factors higher than the percolation threshold. ITO powders are commercially available in an aggregated form and a disaggregation technique was required. Here, aggregated ITO nanoparticles were transformed to colloidal suspension by high-speed stirring. This finely dispersed ceramic suspension was stabilized by addition of poly(vinyl pyrrolidone) and the obtained colloidal system was cast on an optical-grade substrate (PET) to produce electrically conductive-transparent nanocomposite films. Preliminary mechanical and electrical characterization of these films showed good conductivity and interfacial properties

We have fabricated and studied a stacked superconducting double tunnel junction device with transistor-like properties. The intermediate electrode is a bilayer consisting of a Nb film together with an Al film that acts as a quasiparticle trap. Large current gains of more than 50 are observed at 4.2 K when the Al layer is normal. The operation is highly directional. Results are explained on the basis of trapping of quasiparticles from a superconductor into a normal metal, together with a conversion of relaxation energy into electronic excitations. Similar devices should have wide applications in low-temperature measurement and detection systems.