618 research outputs found
Current perpendicular to plane Giant Magnetoresistance (GMR) in laminated nanostructures
We theoretically studied spin dependent electron transport
perpendicular-to-plain (CPP) in magnetic laminated multilayered structures by
using Kubo formalism. We took into account not only bulk scattering, but the
interface resistance due to both specular and diffuse reflection and also spin
conserving and spin-flip processes. It was shown that spin-flip scattering at
interfaces substantially reduces the value of GMR. This can explain the
experimental observations that the CPP GMR ratio for laminated structures only
slightly increases as compared to non-laminated ones despite lamination induces
a significant increase in CPP resistance.Comment: 4 pages, 2 figure
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
Spin Currents Induced by Nonuniform Rashba-Type Spin-Orbit Field
We study the spin relaxation torque in nonmagnetic or ferromagnetic metals
with nonuniform spin-orbit coupling within the Keldysh Green's function
formalism. In non-magnet, the relaxation torque is shown to arise when the
spin-orbit coupling is not uniform. In the absence of an external field, the
spin current induced by the relaxation torque is proportional to the vector
chirality of Rashba-type spin-orbit field (RSOF). In the presence of an
external field, on the other hand, spin relaxation torque arises from the
coupling of the external field and vector chirality of RSOF. Our result
indicates that spin-sink or source effects are controlled by designing RSOF in
junctions.Comment: 3 figure
Power estimation of tests in log-linear non-uniform association models for ordinal agreement
<p>Abstract</p> <p>Background</p> <p>Log-linear association models have been extensively used to investigate the pattern of agreement between ordinal ratings. In 2007, log-linear non-uniform association models were introduced to estimate, from a cross-classification of two independent raters using an ordinal scale, varying degrees of distinguishability between distant and adjacent categories of the scale.</p> <p>Methods</p> <p>In this paper, a simple method based on simulations was proposed to estimate the power of non-uniform association models to detect heterogeneities across distinguishabilities between adjacent categories of an ordinal scale, illustrating some possible scale defects.</p> <p>Results</p> <p>Different scenarios of distinguishability patterns were investigated, as well as different scenarios of marginal heterogeneity within rater. For sample size of N = 50, the probabilities of detecting heterogeneities within the tables are lower than .80, whatever the number of categories. In additition, even for large samples, marginal heterogeneities within raters led to a decrease in power estimates.</p> <p>Conclusion</p> <p>This paper provided some issues about how many objects had to be classified by two independent observers (or by the same observer at two different times) to be able to detect a given scale structure defect. Our results also highlighted the importance of marginal homogeneity within raters, to ensure optimal power when using non-uniform association models.</p
Identification and selection rules of the spin-wave eigen-modes in a normally magnetized nano-pillar
We report on a spectroscopic study of the spin-wave eigen-modes inside an
individual normally magnetized two layers circular nano-pillar
(PermalloyCopperPermalloy) by means of a Magnetic Resonance Force
Microscope (MRFM). We demonstrate that the observed spin-wave spectrum
critically depends on the method of excitation. While the spatially uniform
radio-frequency (RF) magnetic field excites only the axially symmetric modes
having azimuthal index , the RF current flowing through the
nano-pillar, creating a circular RF Oersted field, excites only the modes
having azimuthal index . Breaking the axial symmetry of the
nano-pillar, either by tilting the bias magnetic field or by making the pillar
shape elliptical, mixes different -index symmetries, which can be excited
simultaneously by the RF current. Experimental spectra are compared to
theoretical prediction using both analytical and numerical calculations. An
analysis of the influence of the static and dynamic dipolar coupling between
the nano-pillar magnetic layers on the mode spectrum is performed
Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier
We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds
Mechanisms of spin-polarized current-driven magnetization switching
The mechanisms of the magnetization switching of magnetic multilayers driven
by a current are studied by including exchange interaction between local
moments and spin accumulation of conduction electrons. It is found that this
exchange interaction leads to two additional terms in the
Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both
terms are proportional to the transverse spin accumulation and have comparable
magnitudes
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