492 research outputs found
Bipolar High Field Excitations in Co/Cu/Co Nanopillars
Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars
(50 nm in diameter) have been studied experimentally at low temperatures
for large applied fields perpendicular to the layers. At sufficiently high
current densities excitations, which lead to a decrease in differential
resistance, are observed for both current polarities. Such bipolar excitations
are not expected in a single domain model of spin-transfer. We propose that at
high current densities strong asymmetries in the longitudinal spin accumulation
cause spin-wave instabilities transverse to the current direction in bilayer
samples, similar to those we have reported for single magnetic layer junctions.Comment: 4 pages, 4 figures+ 2 additional jpg figures (Fig. 2d and Fig. 3)
high resolution figures and recent related articles are available at:
http://www.physics.nyu.edu/kentlab/news.htm
Current Induced Excitations in Cu/Co/Cu Single Ferromagnetic Layer Nanopillars
Current-induced magnetic excitations in Cu/Co/Cu single layer nanopillars
(~50 nm in diameter) have been studied experimentally as a function of Co layer
thickness at low temperatures for large applied fields perpendicular to the
layers. For asymmetric junctions current induced excitations are observed at
high current densities for only one polarity of the current and are absent at
the same current densities in symmetric junctions. These observations confirm
recent predictions of spin-transfer torque induced spin wave excitations in
single layer junctions with a strong asymmetry in the spin accumulation in the
leads.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Current-Induced Effective Magnetic Fields in Co/Cu/Co Nanopillars
We present a method to measure the effective field contribution to
spin-transfer-induced interactions between the magnetic layers in a trilayer
nanostructure, which enables spin-current effects to be distinguished from the
usual charge-current-induced magnetic fields. This technique is demonstrated on
submicron Co/Cu/Co nanopillars. The hysteresis loop of one of the magnetic
layers in the trilayer is measured as a function of current while the direction
of magnetization of the other layer is kept fixed, first in one direction and
then in the opposite direction. These measurements show a current-dependent
shift of the hysteresis loop which, based on the symmetry of the magnetic
response, we associate with spin-transfer. The observed loop-shift with applied
current at room temperature is reduced in measurements at 4.2 K. We interprete
these results both in terms of a spin-current dependent effective activation
barrier for magnetization reversal and a spin-current dependent effective
magnetic field. From data at 4.2 K we estimate the magnitude of the
spin-transfer induced effective field to be Oe
cm/A, about a factor of 5 less than the spin-transfer torque.Comment: 6 pages, 4 figure
Current-Induced Magnetization Reversal in High Magnetic Fields in Co/Cu/Co Nanopillars
Current-induced magnetization dynamics in Co/Cu/Co trilayer nanopillars
(~100nm in diameter) has been studied experimentally for large applied fields
perpendicular to the layers. An abrupt and hysteretic increase in dynamic
resistance is observed at high current densities for one polarity of the
current, comparable to the giant magnetoresistance effect observed at low
fields. A micromagnetic model, that includes a spin-transfer torque, suggests
that the current induces a complete reversal of the thin Co layer to alignment
antiparallel to the applied field-that is, to a state of maximum magnetic
energy.Comment: 11 pages, 3 figures, (submitted to Phys. Rev. Lett.), added missing
figure caption of fig. 3, updated to published versio
Reset dynamics and latching in niobium superconducting nanowire single-photon detectors
We study the reset dynamics of niobium (Nb) superconducting nanowire
single-photon detectors (SNSPDs) using experimental measurements and numerical
simulations. The numerical simulations of the detection dynamics agree well
with experimental measurements, using independently determined parameters in
the simulations. We find that if the photon-induced hotspot cools too slowly,
the device will latch into a dc resistive state. To avoid latching, the time
for the hotspot to cool must be short compared to the inductive time constant
that governs the resetting of the current in the device after hotspot
formation. From simulations of the energy relaxation process, we find that the
hotspot cooling time is determined primarily by the temperature-dependent
electron-phonon inelastic time. Latching prevents reset and precludes
subsequent photon detection. Fast resetting to the superconducting state is
therefore essential, and we demonstrate experimentally how this is achieved
Community occupational therapy for people with dementia and their family carers: A national survey of United Kingdom occupational therapy practice
Introduction: A national survey was conducted with United Kingdom (UK) occupational therapists to scope occupational therapy service provision for people with dementia and their family carers in the community. /
Method: This was an online questionnaire with topics on occupational therapists’ roles, service provision, referral, assistive technology and assessment tools. Recruitment was through direct invitation, and promotion via occupational therapy networks, websites and newsletters. /
Results: A total of 197 responded. Occupational therapy referrals most commonly came from the multidisciplinary team. Over half primarily undertook profession-specific work, with occupational therapy assessments the most common profession-specific task. Two-thirds of referrals for initial assessments were for people with mild-to-moderate dementia. A median of 2.5 hours for assessment/intervention was spent for each person with dementia. Almost two-thirds used the Model of Human Occupation Screening Tool. Most could prescribe personal activities of daily living equipment and Telecare, with few able to prescribe equipment for reminiscence or leisure. /
Conclusion: This national survey increases knowledge of UK community occupational therapy practice and service provision for people with dementia and their family carers. It informs occupational therapists about national trends within this practice area, and development of the community occupational therapy intervention (COTiD-UK) as part of the Valuing Active Life in Dementia research programme
Spatial distribution of local currents of massless Dirac fermions in quantum transport through graphene nanoribbons
We employ the formalism of bond currents, expressed in terms of the
nonequilibrium Green functions, to image the charge flow between two sites of
the honeycomb lattice of graphene ribbons of few nanometers width. In sharp
contrast to nonrelativistic electrons, current density profiles of quantum
transport at energies close to the Dirac point in clean zigzag graphene
nanoribbons (ZGNR) differs markedly from the profiles of charge density peaked
at the edges due to zero-energy localized edge states. For transport through
the lowest propagating mode induced by these edge states, edge vacancies do not
affect current density peaked in the center of ZGNR. The long-range potential
of a single impurity acts to reduce local current around it while concurrently
increasing the current density along the zigzag edge, so that ZGNR conductance
remains perfect .Comment: 5 pages, 5 figure
- …