262 research outputs found
Current-induced two-level fluctuations in pseudo spin-valves (Co/Cu/Co) nanostructures
Two-level fluctuations of the magnetization state of pseudo spin-valve
pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires
(~40 nm in diameter, 6000 nm in length) are triggered by spin-polarized
currents of 10^7 A/cm^2 at room temperature. The statistical properties of the
residence times in the parallel and antiparallel magnetization states reveal
two effects with qualitatively different dependences on current intensity. The
current appears to have the effect of a field determined as the bias field
required to equalize these times. The bias field changes sign when the current
polarity is reversed. At this field, the effect of a current density of 10^7
A/cm^2 is to lower the mean time for switching down to the microsecond range.
This effect is independent of the sign of the current and is interpreted in
terms of an effective temperature for the magnetization.Comment: 4 pages, 5 figures, revised version, to be published in Phys. Rev.
Let
Electrochemical Surface Modification of Aluminium Sheets for Application to Nano-electronic Devices: Anodization Aluminium and Electrodeposition of Cobalt-Copper
A nano-porous anodized aluminium oxide layer was synthesized on the surface of bulk aluminium at a wide range of anodization voltages. The barrier layer at the pore bottom of anodized aluminium oxide layer was chemically etched to make good electrical contact for nanowires electrodeposited in the pores thus formed on metallic aluminium substrates. Cathodic polarization was examined at a wide range of cathode potentials to investigate the electrodeposition behaviour of Cu and Co into the pores. Co81Cu19/Cu multilayered nanowires were fabricated using a pulse-plating technique into the templates. Co-alloy layer and Cu layer thicknesses were adjusted to 10 nm, by controlling the deposition times. The temperature dependence of the resistance of Co81Cu19/Cu multilayered nanowires grown on the template presented clean metallic characteristics and a giant magnetoresistance (GMR) of 23% was reached at 4
Spin-dependent transport in cluster-assemblednanostructures: influence of cluster size and matrix material
Abstract.: Spin-dependent transport in granular metallic nanostructures has been investigated by means of a thermoelectric measurement. Cobalt clusters of well-defined size (〈n〉 = 15-600) embedded in copper and silver matrices show magnetic field responses of up to several hundred percent at low temperature. The experimental observations are attributed to spin mixing. The influence of cluster size and matrix are discusse
Characterizing extremal digraphs for identifying codes and extremal cases of Bondy's theorem on induced subsets
An identifying code of a (di)graph is a dominating subset of the
vertices of such that all distinct vertices of have distinct
(in)neighbourhoods within . In this paper, we classify all finite digraphs
which only admit their whole vertex set in any identifying code. We also
classify all such infinite oriented graphs. Furthermore, by relating this
concept to a well known theorem of A. Bondy on set systems we classify the
extremal cases for this theorem
Processing Distinct Linguistic Information Types in Working Memory in Aphasia
This investigation measured performance of individuals with aphasia on working memory tasks targeting their processing of different information types (phonological, semantic, and structural/syntactic). Participants included 3 adults with aphasia. Tasks included a listening span and three novel n-back tasks. The n-back tasks were presented auditorily, and measured both active working memory maintenance ("identity" level) and processing ("depth" level) for each information type. Results indicate that the tasks may be able to differentiate individual performance along the lines of aphasia classification categories, suggesting that the modified n-back tasks may lead to a more precise description of aphasic performance
Fermi-Edge Singularities in AlxGa1-xAs Quantum Wells : Extrinsic Versus Many-Body Scattering Processes
A Fano resonance mechanism is evidenced to control the formation of optical
Fermi-edge singularities in multi-subband systems such as remotely doped
AlxGa1-xAs heterostructures. Using Fano parameters, we probe the physical
nature of the interaction between Fermi-sea electrons and empty conduction
subbands. We show that processes of extrinsic origin like alloy-disorder
prevail easily at 2D over multiple diffusions from charged valence holes
expected by many-body scenarios.Comment: 4 pages, 3 figures, accepted for publication in Physical Review
Letter
Seebeck Effect in Magnetic Tunnel Junctions
Creating temperature gradients in magnetic nanostructures has resulted in a
new research direction, i.e., the combination of magneto- and thermoelectric
effects. Here, we demonstrate the observation of one important effect of this
class: the magneto-Seebeck effect. It is observed when a magnetic configuration
changes the charge based Seebeck coefficient. In particular, the Seebeck
coefficient changes during the transition from a parallel to an antiparallel
magnetic configuration in a tunnel junction. In that respect, it is the analog
to the tunneling magnetoresistance. The Seebeck coefficients in parallel and
antiparallel configuration are in the order of the voltages known from the
charge-Seebeck effect. The size and sign of the effect can be controlled by the
composition of the electrodes' atomic layers adjacent to the barrier and the
temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which
results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to
the parallel direction close to the predicted value of -12.1 {\mu}V/K.Comment: 16 pages, 7 figures, 2 table
Photoluminescence investigations of 2D hole Landau levels in p-type single Al_{x}Ga_{1-x}As/GaAs heterostructures
We study the energy structure of two-dimensional holes in p-type single
Al_{1-x}Ga_{x}As/GaAs heterojunctions under a perpendicular magnetic field.
Photoluminescence measurments with low densities of excitation power reveal
rich spectra containing both free and bound-carrier transitions. The
experimental results are compared with energies of valence-subband Landau
levels calculated using a new numerical procedure and a good agreement is
achieved. Additional lines observed in the energy range of free-carrier
recombinations are attributed to excitonic transitions. We also consider the
role of many-body effects in photoluminescence spectra.Comment: 13 pages, 10 figures, accepted to Physical Review
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