1,259 research outputs found
Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets
Envisaged applications of skyrmions in magnetic memory and logic devices
crucially depend on the stability and mobility of these topologically
non-trivial magnetic textures in thin films. We present for the first time
quantitative maps of the magnetic induction that provide evidence for a 3D
modulation of the skyrmionic spin texture. The projected in-plane magnetic
induction maps as determined from in-line and off-axis electron holography
carry the clear signature of Bloch skyrmions. However, the magnitude of this
induction is much smaller than the values expected for homogeneous Bloch
skyrmions that extend throughout the thickness of the film. This finding can
only be understood, if the underlying spin textures are modulated along the
out-of-plane z direction. The projection of (the in-plane magnetic induction
of) helices is further found to exhibit thickness-dependent lateral shifts,
which show that this z modulation is accompanied by an (in-plane) modulation
along the x and y directions
Coherence Properties of the Repulsive Anyon-Hubbard Dimer
One-dimensional anyonic models of the Hubbard type show intriguing
ground-state properties, effectively transmuting between Bose-Einstein and
Fermi-Dirac statistics. The simplest model that one can investigate is an
anyonic version of the bosonic Josephson junction, the repulsive anyon-Hubbard
dimer. In the following we find an exact duality relation to the Bethe-solvable
Bose-Hubbard dimer, which is well known from quantum optics and information
theory and has interesting connections to spin squeezing and entangled coherent
states. Conversely, we show that the anyonic Hubbard dimer has non-trivial
coherence properties for large particle numbers, which can potentially be
probed by cold atom experiments. We find that the statistical interactions act
as excitation-selective filters or amplifiers for large particle numbers ,
determining the fate of multi-body coherences depending on their
commensurability with respect to the exchange parameter .Comment: 8 pages, 2 figures, for more information and latest version see
https://www.physik.uni-kl.de/eggert/papers
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Control of positive and negative magnetoresistance in iron oxideâiron nanocomposite thin films for tunable magnetoelectric nanodevices
The perspective of energy-efficient and tunable functional magnetic nanostructures has triggered research efforts in the fields of voltage control of magnetism and spintronics. We investigate the magnetotransport properties of nanocomposite iron oxide/iron thin films with a nominal iron thickness of 5-50 nm and find a positive magnetoresistance at small thicknesses. The highest magnetoresistance was found for 30 nm Fe with +1.1% at 3 T. This anomalous behavior is attributed to the presence of Fe3O4-Fe nanocomposite regions due to grain boundary oxidation. At the Fe3O4/Fe interfaces, spin-polarized electrons in the magnetite can be scattered and reoriented. A crossover to negative magnetoresistance (â0.11%) is achieved at a larger thickness (>40 nm) when interface scattering effects become negligible as more current flows through the iron layer. Electrolytic gating of this system induces voltage-triggered redox reactions in the Fe3O4 regions and thereby enables voltage-tuning of the magnetoresistance with the locally oxidized regions as the active tuning elements. In the low-magnetic-field region (<1 T), a crossover from positive to negative magnetoresistance is achieved by a voltage change of only 1.72 V. At 3 T, a relative change of magnetoresistance about â45% during reduction was achieved for the 30 nm Fe sample. The present low-voltage approach signifies a step forward to practical and tunable room-temperature magnetoresistance-based nanodevices, which can boost the development of nanoscale and energy-efficient magnetic field sensors with high sensitivity, magnetic memories, and magnetoelectric devices in general
Spectral Decomposition of Broad-Line AGNs and Host Galaxies
Using an eigenspectrum decomposition technique, we separate the host galaxy
from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from
the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75.
The decomposition technique uses separate sets of galaxy and quasar
eigenspectra to efficiently and reliably separate the AGN and host
spectroscopic components. The technique accurately reproduces the host galaxy
spectrum, its contributing fraction, and its classification. We show how the
accuracy of the decomposition depends upon S/N, host galaxy fraction, and the
galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN
host galaxies spans a wide range of spectral types, but the distribution
differs significantly from inactive galaxies. In particular, post-starburst
activity appears to be much more common among AGN host galaxies. The
luminosities of the hosts are much higher than expected for normal early-type
galaxies, and their colors become increasingly bluer than early-type galaxies
with increasing host luminosity. Most of the AGNs with detected hosts are
emitting at between 1% and 10% of their estimated Eddington luminosities, but
the sensitivity of the technique usually does not extend to the Eddington
limit. There are mild correlations among the AGN and host galaxy
eigencoefficients, possibly indicating a link between recent star formation and
the onset of AGN activity. The catalog of spectral reconstruction parameters is
available as an electronic table.Comment: 18 pages; accepted for publication in A
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VoltageâControlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites
High energy efficiency of magnetic devices is crucial for applications such as data storage, computation, and actuation. Redoxâbased (magnetoâionic) voltage control of magnetism is a promising roomâtemperature pathway to improve energy efficiency. However, for ferromagnetic metals, the magnetoâionic effects studied so far require ultrathin films with tunable perpendicular magnetic anisotropy or nanoporous structures for appreciable effects. This paper reports a fully reversible, low voltageâinduced collapse of coercivity and remanence by redox reactions in iron oxide/iron films with uniaxial inâplane anisotropy. In the initial iron oxide/iron films, NĂ©el wall interactions stabilize a blocked state with high coercivity. During the voltageâtriggered reduction of the iron oxide layer, in situ Kerr microscopy reveals inverse changes of coercivity and anisotropy, and a coarsening of the magnetic microstructure. These results confirm a magnetoâionic deblocking mechanism, which relies on changes of the NĂ©el wall interactions, and of the microstructural domainâwallâpinning sites. With this approach, voltageâcontrolled 180° magnetization switching with high energyâefficiency is achieved. It opens up possibilities for developing magnetic devices programmable by ultralow power and for the reversible tuning of defectâcontrolled materials in general
Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio
Virtual Reality Exposure to a Healthy Weight Body Is a Promising Adjunct Treatment for Anorexia Nervosa
Introduction/objective: Treatment results of anorexia nervosa (AN) are modest, with fear of weight gain being a strong predictor of treatment outcome and relapse. Here, we present a virtual reality (VR) setup for exposure to healthy weight and evaluate its potential as an adjunct treatment for AN. Methods: In two studies, we investigate VR experience and clinical effects of VR exposure to higher weight in 20 women with high weight concern or shape concern and in 20 women with AN. Results: In study 1, 90% of participants (18/20) reported symptoms of high arousal but verbalized low to medium levels of fear. Study 2 demonstrated that VR exposure to healthy weight induced high arousal in patients with AN and yielded a trend that four sessions of exposure improved fear of weight gain. Explorative analyses revealed three clusters of individual reactions to exposure, which need further exploration. Conclusions: VR exposure is a well-accepted and powerful tool for evoking fear of weight gain in patients with AN. We observed a statistical trend that repeated virtual exposure to healthy weight improved fear of weight gain with large effect sizes. Further studies are needed to determine the mechanisms and differential effects
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