1,184 research outputs found
Spin-Transfer Torque Induced Vortex Dynamics in Fe/Ag/Fe Nanopillars
We report experimental and analytical work on spin-transfer torque induced
vortex dynamics in metallic nanopillars with in-plane magnetized layers. We
study nanopillars with a diameter of 150 nm, containing two Fe layers with a
thickness of 15 nm and 30 nm respectively, separated by a 6 nm Ag spacer. The
sample geometry is such that it allows for the formation of magnetic vortices
in the Fe disks. As confirmed by micromagnetic simulations, we are able to
prepare states where one magnetic layer is homogeneously magnetized while the
other contains a vortex. We experimentally show that in this configuration
spin-transfer torque can excite vortex dynamics and analyze their dependence on
a magnetic field applied in the sample plane. The center of gyration is
continuously dislocated from the disk center, and the potential changes its
shape with field strength. The latter is reflected in the field dependence of
the excitation frequency. In the second part we propose a novel mechanism for
the excitation of the gyrotropic mode in nanopillars with a perfectly
homogeneously magnetized in-plane polarizing layer. We analytically show that
in this configuration the vortex can absorb energy from the spin-polarized
electric current if the angular spin-transfer efficiency function is
asymmetric. This effect is supported by micromagnetic simulations.Comment: The article has been sent to J. Phys. D. Submitted on August 9, 2010.
(7 pages and 4 figures.
Spin-dependent electronic hybridization in a rope of carbon nanotubes
We demonstrate single electron addition to different strands of a carbon
nanotube rope. Anticrossings of anomalous conductance peaks occur in quantum
transport measurements through the parallel quantum dots forming on the
individual strands. We determine the magnitude and the sign of the
hybridization as well as the Coulomb interaction between the carbon nanotube
quantum dots, finding that the bonding states dominate the transport. In a
magnetic field the hybridization is shown to be selectively suppressed due to
spin effects.Comment: 4 pages, 4 figure
Impact of tunnel barrier strength on magnetoresistance in carbon nanotubes
We investigate magnetoresistance in spin valves involving CoPd-contacted
carbon nanotubes. Both temperature and bias voltage dependence clearly indicate
tunneling magnetoresistance as the origin. We show that this effect is
significantly affected by the tunnel barrier strength, which appears to be one
reason for the variation between devices previously detected in similar
structures. Modeling the data by means of the scattering matrix approach, we
find a non-trivial dependence of the magnetoresistance on the barrier strength.
Furthermore, analysis of the spin precession observed in a nonlocal Hanle
measurement yields a spin lifetime of ns, a value comparable
with those found in silicon- or graphene-based spin valve devices.Comment: 10 pages, 5 figures, 1 tabl
Taking the Perfect Selfie: Investigating the Impact of Perspective on the Perception of Higher Cognitive Variables
Taking selfies is now becoming a standard human habit. However, as a social phenomenon, research is still in the fledgling stage and the scientific framework is sparse. Selfies allow us to share social information with others in a compact format. Furthermore, we are able to control important photographic and compositional aspects, such as perspective, which have a strong impact on the assessment of a face (e.g., demonstrated by the height-weight illusion, effects of gaze direction, faceism-index). In Study 1, we focused on the impact of perspective (left/right hemiface, above/below vs. frontal presentation) on higher cognitive variables and let 172 participants rate the perceived attractiveness, helpfulness, sympathy, dominance, distinctiveness, and intelligence, plus important information on health issues (e.g., body weight), on the basis of 14 3D faces. We could show that lateral snapshots yielded higher ratings for attractiveness compared to the classical frontal view. However, this effect was more pronounced for left hemifaces and especially female faces. Compared to the frontal condition, 30° right hemifaces were rated as more helpful, but only for female faces while faces viewed from above were perceived as significant less helpful. Direct comparison between left vs. right hemifaces revealed no effect. Relating to sympathy, we only found a significant effect for 30° right male hemifaces, but only in comparison to the frontal condition. Furthermore, female 30° right hemifaces were perceived as more intelligent. Relating to body weight, we replicated the so-called “height-weight illusion.” Other variables remained unaffected. In Study 2, we investigated the impact of a typical selfie-style condition by presenting the respective faces from a lateral (left/right) and tilted (lower/higher) vantage point. Most importantly, depending on what persons wish to express with a selfie, a systematic change of perspective can strongly optimize their message; e.g., increasing their attractiveness by shooting from above left, and in contrast, decreasing their expressed helpfulness by shooting from below. We could further extent past findings relating to the height-weight illusion and showed that an additional rotation of the camera positively affected the perception of body weight (lower body weight). We discuss potential explanations for perspective-related effects, especially gender-related ones
Ultrafast dynamics of a magnetic antivortex - Micromagnetic simulations
The antivortex is a fundamental magnetization structure which is the
topological counterpart of the well-known magnetic vortex. We study here the
ultrafast dynamic behavior of an isolated antivortex in a patterned Permalloy
thin-film element. Using micromagnetic simulations we predict that the
antivortex response to an ultrashort external field pulse is characterized by
the production of a new antivortex as well as of a temporary vortex, followed
by an annihilation process. These processes are complementary to the recently
reported response of a vortex and, like for the vortex, lead to the reversal of
the orientation of the antivortex core region. In addition to its fundamental
interest, this dynamic magnetization process could be used for the generation
and propagation of spin waves for novel logical circuits.Comment: 4 pages, 4 figures. To be published in Physical Review B (R
Human Skin Permeation Enhancement Using PLGA Nanoparticles Is Mediated by Local pH Changes
The steady improvement and optimization of transdermal permeation is a constant and
challenging pharmaceutical task. In this study the influence of poly(lactide-co-glycolide) (PLGA)
nanoparticles on the dermal permeation of the anti-inflammatory drug flufenamic acid (FFA) was
investigated. For this aim, different vehicles under non-buffered and buffered conditions and different
skin models (human heat separated epidermis and reconstructed human epidermis equivalents)
were tested. Permeation experiments were performed using static Franz diffusion cells under infinite
dosing conditions. Already the presence of drug-free nanoparticles increased drug permeation
across the skin. Drug permeation was even enhanced when applying drug-loaded nanoparticles. In
contrast, buffered vehicles with different pH values (pH 5.4–7.4) revealed the influence of the pH
on the permeation of FFA. The change of the surrounding pH of the biodegradable nanoparticulate
system was demonstrated and visualized using pH-sensitive fluorescent probes. While a potential
contribution of hair follicles could be ruled out, our data suggest that the enhanced permeation of
FFA through human skin in the presence of PLGA nanoparticles is mediated by a locally decreased
pH during hydrolytic degradation of this polymer. This hypothesis is supported by the observation
that skin permeation of the weak base caffeine was not affected
Spatially resolved observation of uniform precession modes in spin-valve systems
Using time-resolved photoemission electron microscopy the excitation of
uniform precession modes in individual domains of a weakly coupled spin-valve
system has been studied. A coupling dependence of the precession frequencies
has been found that can be reasonably well understood on the basis of a
macrospin model. By tuning the frequency of the excitation source the uniform
precession modes are excited in a resonant way.Comment: This article has been accepted by Journal of Applied Physics. After
it is published, it will be found at http://jap.aip.or
Non-innocent role of fluorine as an electron donor in oxides
Engineering of reducible oxides is generally focused on the cation sites. As such, anion doping remains an underutilized tool despite its unique potential in altering the defect chemistry and steering redox processes. In this contribution, we explore the possibilities offered by substitution on the anion site on the case of a prototypical reducible oxide, namely cerium oxide, doped with fluorine. The choice of fluorine is motivated by the general stability of fluorine in oxide lattices and the fact that it can be readily incorporated in these up to very high concentration with minimal structural distortion [1]. Utilizing photoemission spectroscopy in combination with density functional theory [2], we show that the general notion of fluorine acting as a straightforward ionic donor fails to capture the intricacies of electronic interactions at play. Specifically, we provide evidence for covalent hybridization in the nominally ionic fluorine-cerium interaction that allows for altering the anion derived electron density in cerium oxide beyond the oxygen 2p band (see Figure 1), contrary to the simplified picture of solely introducing a deeper-laying fluorine 2p band [3]. The emergent electronic configuration can be further coupled to standard valence band engineering methods, such as strain manipulation, to provide an unprecedented playground for designing the oxide properties. Our results also demonstrate the practicality of interatomic resonant photoemission spectroscopy as a gauge of non-trivial electronic effects of ligand origin, allowing to efficiently probe the above-mentioned effects. We note that fluorine doping represents a complement to oxygen vacancy engineering and highlight the fact that, unlike oxygen vacancies, the electronic effects generated by fluorine can persist in an oxidizing environment. The latter represents an important contribution the electronic modification of mixed-anion oxides can provide to a breadth of fields, ranging from superoxide stabilization to resistive switching.
Please click Additional Files below to see the full abstract
Nanoscale X-ray investigation of magnetic metallofullerene peapods
Endohedral lanthanide ions packed inside carbon nanotubes (CNTs) in a
one-dimensional assembly have been studied with a combination of high
resolution transmission electron microscopy (HRTEM), scanning transmission
X-ray microscopy (STXM), and X-ray magnetic circular dichroism (XMCD). By
correlating HRTEM and STXM images we show that structures down to 30 nm are
resolved with chemical contrast and record X-ray absorption spectra from
endohedral lanthanide ions embedded in individual nanoscale CNT bundles. XMCD
measurements of an ErN@C bulk sample and a macroscopic assembly of
filled CNTs indicates that the magnetic properties of the endohedral Er3+ ions
are unchanged when encapsulated in CNTs. This study demonstrates the
feasibility of local magnetic X-ray characterization of low concentrations of
lanthanide ions embedded in molecular nanostructures
- …