The spin-coherent quantum transport through multiwall carbon nanotubes contacted by ferromagnetic Co pads is investigated experimentally. At 4.2 K, the devices show a remarkable increase of the magnetoresistance (MR) ratio with decreasing junction bias, reaching a maximum MR ratio of 30% at a junction bias current of 1 nA. The experimental results suggest the transport to be dominated by spin-dependent tunneling processes at the Co/nanotube interfaces and governed by the local magnetization. We also observe an asymmetry of the magnetoresistance peak position and width which is attributed to a local exchange biasing in the electrode material.

This paper concerns with giant magnetoresistance (MR) effects in organic spin valves, which are realized as layered (La,Sr)MnO3 (LSMO)-based junctions with tris-(8, hydroxyquinoline) aluminum (Alq3)-spacer and ferromagnetic top layers. The experimental work was focused on the understanding of the transport behavior in this type of magnetic switching elements. The device preparation was carried out in an ultrahigh vacuum chamber equipped with a mask changer by evaporation and sputtering on SrTiO3 substrates with LSMO stripes deposited by pulsed laser technique. The field and temperature dependences of the MR of the prepared elements are studied. Spin-valve effects at 4.2K have been observed in a broad resistance interval from 50Ω to MΩ range, however, without systematic dependence on spacer layer thickness and device area. In some samples, the MR changes sign as a function of the bias voltage. The observed similarity in the bias voltages dependences of the MR in comparison with conventional magnetic tunnel junctions with oxide barriers suggests a description of the found effects within the classical tunneling concept. This assumption is also confirmed by a similar switching behavior observed on ferromagnetically contacted carbon nanotube devices. The proposed model implies the realization of the transport via local Co chains embedded in the Alq3 layer and spin dependent tunneling over barriers at the interface Co grains∕Alq3∕LSMO. The existence of conducting Co chains within the organics is supported by transmission electron microscopic∕electron energy loss spectroscopic studies on cross-sectional samples from analogous layer stacks.

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Superconductor/ferromagnet (S/F) proximity effect theory predicts that the superconducting critical temperature of the F1/F2/S or F1/S/F2 trilayers for the parallel orientation of the F1 and F2 magnetizations is smaller than for the antiparallel one. This suggests a possibility of a controlled switching between the superconducting and normal states in the S layer. Here, using the spin switch design F1/F2/S theoretically proposed by Oh et al. [Appl. Phys. Lett. 71, 2376], that comprises a ferromagnetic bilayer separated by a non-magnetic metallic spacer layer as a ferromagnetic component, and an ordinary superconductor as the second interface component, we have successfully realized a full spin switch effect for the superconducting current.

We study the metal-insulator transition in two sets of amorphous Si 1−x Ni x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, energy dispersive X-ray analysis, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w = d ln σ/d ln T , we observe that, for insulating samples, w(T ) shows a minimum, increasing at both low and high T . Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of w(T, x) leads to the conclusion that the transition in Si 1−x Ni x is very likely discontinuous at zero temperature in agreement with Mott's original views. 71.30.+h,71.23.Cq, Typeset using REVT E X

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We report an electrical-field-controlled growth process for the directed bottom-up assembly of one-dimensional palladium nanowires between microfabricated electrodes. The wires, grown from an aqueous palladium salt solution by dielectrophoresis, have a thickness of only 5-10 nm and a length of up to several micrometers. The growth process depends largely on both the strength of the applied ac field and the concentration of the metal salt solution. The conditions for optimum growth are evaluated. Room-temperature current-voltage measurements show ohmic behavior and indicate electromigration effects at higher voltages. Low-temperature transport measurements reveal localization effects with a characteristic resistance minimum at 20 K. The temperature dependence below the minimum shows the wires to be one dimensional in their electron-transport properties. The investigated growth method is capable of building complex circuit patterns for future nanoelectronics.

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