306 research outputs found
Effect of interface bonding on spin-dependent tunneling from the oxidized Co surface
We demonstrate that the factorization of the tunneling transmission into the
product of two surface transmission functions and a vacuum decay factor allows
one to generalize Julliere's formula and explain the meaning of the ``tunneling
density of states'' in some limiting cases. Using this factorization we
calculate spin-dependent tunneling from clean and oxidized fcc Co surfaces
through vacuum into Al using the principal-layer Green's function approach. We
demonstrate that a monolayer of oxygen on the Co (111) surface creates a
spin-filter effect due to the Co-O bonding which produces an additional
tunneling barrier in the minority-spin channel. This changes the minority-spin
dominated conductance for the clean Co surface into a majority spin dominated
conductance for the oxidized Co surface.Comment: 7 pages, revtex4, 4 embedded eps figure
Spin-dependent Seebeck coefficients of Ni_{80}Fe_{20} and Co in nanopillar spin valves
We have experimentally determined the spin-dependent Seebeck coefficient of
permalloy (Ni_{80}Fe_{20}) and cobalt (Co) using nanopillar spin valve devices.
The devices were specifically designed to completely separate heat related
effects from charge related effects. A pure heat current through the nanopillar
spin valve, a stack of two ferromagnetic layers (F) separated by a non-magnetic
layer (N), leads to a thermovoltage proportional to the spin-dependent Seebeck
coefficient S_{S}=S_{\uparrow}-S_{\downarrow} of the ferromagnet, where
S_{\uparrow} and S_{\downarrow} are the Seebeck coefficient for spin-up and
spin-down electrons. By using a three-dimensional finite-element model (3D-FEM)
based on spin-dependent thermoelectric theory, whose input material parameters
were measured in separate devices, we were able to accurately determine a
spin-dependent Seebeck coefficient of -1.8 microvolt/Kelvin and -4.5
microvolt/Kelvin for cobalt and permalloy, respectively corresponding to a
Seebeck coefficient polarization P_{S}=S_{S}/S_{F} of 0.08 and 0.25, where
S_{F} is the Seebeck coefficient of the ferromagnet. The results are in
agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent
Seebeck and spin-dependent Peltier measurements in Ni_{80}Fe_{20}/Cu spin valve
structures
Using single quantum states as spin filters to study spin polarization in ferromagnets
By measuring electron tunneling between a ferromagnet and individual energy
levels in an aluminum quantum dot, we show how spin-resolved quantum states can
be used as filters to determine spin-dependent tunneling rates. We also observe
magnetic-field-dependent shifts in the magnet's electrochemical potential
relative to the dot's energy levels. The shifts vary between samples and are
generally smaller than expected from the magnet's spin-polarized density of
states. We suggest that they are affected by field-dependent charge
redistribution at the magnetic interface.Comment: 4 pages, 1 color figur
Emerging materials for spin-charge interconversion
International audienc
Enhanced tunneling magnetoresistance in FeZnSe double junctions
We calculate the tunneling magnetoresistance (TMR) of
FeZnSeFeZnSeFe (001) double magnetic tunnel junctions
as a function of the in-between Fe layer's thickness, and compare these results
with those of FeZnSeFe simple junctions. The electronic band
structures are modeled by a parametrized tight-binding Hamiltonian fitted to
{\it ab initio} calculations, and the conductance is calculated within the
Landauer formalism expressed in terms of Green's functions. We find that the
conductances for each spin channel and the TMR strongly depend on the
in-between Fe layer's thickness, and that in some cases they are enhanced with
respect to simple junctions, in qualitative agreement with recent experimental
studies performed on similar systems. By using a 2D double junction as a
simplified system, we show that the conductance enhancement can be explained in
terms of the junctions energy spectrum. These results are relevant for
spintronics because they demonstrate that the TMR in double junctions can be
tuned and enhanced by varying the in-between metallic layer's thickness.Comment: 200
Scattering theory of interface resistance in magnetic multilayers
The scattering theory of transport has to be applied with care in a diffuse
environment. Here we discuss how the scattering matrices of heterointerfaces
can be used to compute interface resistances of dirty magnetic multilayers.
First principles calculations of these interface resistances agree well with
experiments in the CPP (current perpendicular to the interface plane)
configuration.Comment: submitted to J. Phys. D (special issue at the occasion of Prof. T.
Shinjo's 60th birthday
Spectroscopic time-series analysis of R Canis Majoris
R Canis Majoris is the prototype of a small group of Algol-type stars showing
short orbital periods and low mass ratios. A previous detection of short-term
oscillations in its light curve has not yet been confirmed. We investigate a
new time series of high-resolution spectra with the aim to derive improved
stellar and system parameters, to search for the possible impact of a third
component in the observed spectra, to look for indications of activity in the
Algol system, and to search for short-term variations in radial velocities. We
disentangled the composite spectra into the spectra of the binary components.
Then we analysed the resulting high signal-to-noise spectra of both stars.
Using a newly developed program code based on an improved method of
least-squares deconvolution, we were able to determine the radial velocities of
both components also during primary eclipse. This allowed us to develop a
better model of the system including the Rossiter-McLaughlin effect and to
derive improved orbital parameters. Combining the results with those from
spectrum analysis, we obtain accurate stellar and system parameters. We further
deduce at least one oscillation frequency of 21.38 c/d. It could be detected
during primary eclipses only and confirms a previous photometric finding.
Results point to an amplitude amplification of non-radial pulsation modes due
to the eclipse mapping effect. The presence of a He\,I line in the spectra
indicates mass transfer in the R CMa system. Calculations of its Roche geometry
give evidence that the cool secondary component may fill its Roche lobe. No
evidence of a third body in the system could be found in the observed spectra.Comment: 12 pages, 14 figures, 5 table
PROJECT SUCCESS AND INDIVIDUAL ENTREPRENEURIAL ORIENTATION OF PROJECT MANAGERS: RUSSIAN CONTEXT
Projects implemented in conditions of high uncertainty are sometimes called entrepreneurial projects. Success in such projects is more difficult to achieve. To successfully manage entrepreneurial projects, project managers should have entrepreneurial skills. The article explores two issues related to project success, entrepreneurial characteristics, and project uncertainty. First, the article tries to find out whether the increase in the entrepreneurial nature of the project, manifested in the increase in project goals and methods uncertainty, is accompanied by a decrease in project success. Second question is – does the entrepreneurial orientation of project managers affect project success and the relationship between the projects’ success and their entrepreneurial features. To answer these questions, data were collected from Russian project managers assessing the entrepreneurial nature of projects, project success and the individual entrepreneurial orientation of project-managers. The collected data were examined using factor and regression analysis. The findings indicate that there is a negative relationship between the entrepreneurial nature and such indicators of project success as internal efficiency, preparation for the future, and results for clients. Some indicators of success were positively associated with such indicators of entrepreneurial orientation as proactivity and risk taking. As uncertainty increased, some measures of individual entrepreneurial orientation of project managers can positively compensate negative impact on project success from uncertainty associated with projects’ entrepreneurial nature
Ferroelectric Dead Layer Driven by a Polar Interface
Based on first-principles and model calculations we investigate the effect of
polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As
a representative model, we consider a TiO2-terminated BaTiO3 film with LaO
monolayers at the two interfaces that serve as doping layers. We find that the
polar interfaces create an intrinsic electric field that is screened by the
electron charge leaking into the BaTiO3 layer. The amount of the leaking charge
is controlled by the boundary conditions which are different for three
heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and
SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements
in BaTiO3 to produce the electric polarization directed into the interior of
the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces
that is non-switchable and thus detrimental to ferroelectricity. Our
first-principles and model calculations demonstrate that the effect is stronger
for a larger effective ionic charge at the interface and longer screening
length due to a stronger intrinsic electric field that penetrates deeper into
the ferroelectric. The predicted mechanism for a ferroelectric dead layer at
the interface controls the critical thickness for ferroelectricity in systems
with polar interfaces.Comment: 33 Pages, 5 figure
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