210 research outputs found
Correlation between magnetism and spin-dependent transport in CoFeB alloys
We report a correlation between the spin polarization of the tunneling
electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a
correlation is surprising since the TSP involves s-like electrons close to the
Fermi level (EF), while the magnetic moment mainly arises due to all
d-electrons below EF. We show that probing the s and d-bands individually
provides clear and crucial evidence for such a correlation to exist through s-d
hybridization, and demonstrate the tuneability of the electronic and magnetic
properties of CoFeB alloys.Comment: Accepted for publication in Physical Review Letters. Letter (4 pages)
and Supplementary material (4 pages
Large magnetoresistance using hybrid spin filter devices
A magnetic "spin filter" tunnel barrier, sandwiched between a non-magnetic
metal and a magnetic metal, is used to create a new magnetoresistive tunnel
device, somewhat analogous to an optical polarizer-analyzer configuration. The
resistance of these trilayer structures depends on the relative magnetization
orientation of the spin filter and the ferromagnetic electrode. The spin
filtering in this configuration yields a previously unobserved
magnetoresistance effect, exceeding 100%.Comment: 3.5 pages, 3 figures, submitted to Appl. Phys. Let
Ornstein-Uhlenbeck parameter extraction from light curves of Fermi-LAT observed blazars
Context. Monthly-binned gamma-ray light curves of 236 bright gamma-ray
sources, particularly blazars, selected from a sample of 2278 high-galactic
latitude objects observed with Fermi-LAT, show flux variability characterized
by power spectral densities consisting of a single power-law component, ranging
from Brownian to white noise. Aims. The main goal here is to assess the
Ornstein-Uhlenbeck (OU) model by studying the range of its three parameters
that reproduces these statistical properties. Methods. We develop procedures
for extracting values of the three OU model parameters (mean flux, correlation
length, and random amplitude) from time series data, and apply them to compare
numerical integrations of the OU process with the Fermi-LAT data. Results. The
OU process fully describes the statistical properties of the flux variations of
the 236 blazars. The distributions of the extracted OU parameters are narrowly
peaked about well-defined values (sigma, mu, theta) = (0.2, -8.4, 0.5) with
variances (0.004, 0.07, 0.13). The distributions of rise and decay time scales
of flares in the numerical simulations, i.e. major flux variations fulfilling
pre-defined criteria, are in agreement with the observed ones. The power
spectral densities of the synthetic light curves are statistically
indistinguishable from those of the measured light curves. Conclusions.
Long-term gamma-ray flux variability of blazars on monthly time scales is well
described by a stochastic model involving only three parameters. The methods
described here are powerful tools to study randomness in light curves and
thereby constrain the physical mechanisms responsible for the observed flux
variations.Comment: 13 pages, 9 figure
Use of portable FTIR spectrometers for detecting greenhouse gas emissions of the megacity Berlin - Part 2: Observed time series of XCOâ‚‚ and XCHâ‚„
Five portable Bruker EM27/SUN FTIR spectrometers have been used for the accurate and precise observation of column averaged abundances of CO2 and CH4 around the megacity Berlin. In the first part of this work (Frey et al., 2015) we have presented the various measures that were undertaken to ensure that the observations are consistent between sites, accurate and precise. Here, we present the recorded time series of XCH4 and XCO2 and demonstrate that the CO2 emissions of Berlin can be clearly identified in the observations. A simple dispersion model is applied which indicates a total strength of the Berlin source of about 0.8 t CO2 s-1. In the Supplement of this work, we provide the measured dataset and auxiliary data. We hope that the model community will exploit this unique dataset for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area
Application of portable FTIR spectrometers for detecting greenhouse gas emissions of the major city Berlin
Five portable Bruker EM27/SUN FTIR (Fourier transform infrared) spectrometers have been used for the accurate and precise observation of column-averaged abundances of CO2 and CH4 around the major city Berlin. In the work by Frey et al. (2015), a calibration procedure is developed and applied to the set of spectrometers used for the Berlin campaign. Here, we describe the observational setup of the campaign and aspects of the data analysis, and we present the recorded time series of XCH4 and XCO2. We demonstrate that the CO2 emissions of Berlin can be clearly identified in the observations. A simple dispersion model is applied which indicates a total strength of the Berlin source of about 0.8 t CO2 s-1. In the Supplement of this work, we provide the measured data set and auxiliary data. We hope that the model community will exploit this unique data set for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area. © Author(s) 2015
Critical Susceptibility Exponent Measured from Fe/W(110) Bilayers
The critical phase transition in ferromagnetic ultrathin Fe/W(110) films has
been studied using the magnetic ac susceptibility. A statistically objective,
unconstrained fitting of the susceptibility is used to extract values for the
critical exponent (gamma), the critical temperature Tc, the critical amplitude
(chi_o) and the range of temperature that exhibits power-law behaviour. A
fitting algorithm was used to simultaneously minimize the statistical variance
of a power law fit to individual experimental measurements of chi(T). This
avoids systematic errors and generates objective fitting results. An ensemble
of 25 measurements on many different films are analyzed. Those which permit an
extended fitting range in reduced temperature lower than approximately .00475
give an average value gamma=1.76+-0.01. Bilayer films give a weighted average
value of gamma = 1.75+-0.02. These results are in agreement with the
-dimensional Ising exponent gamma= 7/4. Measurements that do not exhibit
power-law scaling as close to Tc (especially films of thickness 1.75ML) show a
value of gamma higher than the Ising value. Several possibilities are
considered to account for this behaviour.Comment: -Submitted to Phys. Rev. B -Revtex4 Format -6 postscript figure
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