428 research outputs found

### 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

### 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
(Permalloy$|$Copper$|$Permalloy) 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 $\ell=0$, the RF current flowing through the
nano-pillar, creating a circular RF Oersted field, excites only the modes
having azimuthal index $\ell=+1$. Breaking the axial symmetry of the
nano-pillar, either by tilting the bias magnetic field or by making the pillar
shape elliptical, mixes different $\ell$-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

### 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

### Solar Magnetic Field Reversals and the Role of Dynamo Families

The variable magnetic field of the solar photosphere exhibits periodic
reversals as a result of dynamo activity occurring within the solar interior.
We decompose the surface field as observed by both the Wilcox Solar Observatory
and the Michelson Doppler Imager into its harmonic constituents, and present
the time evolution of the mode coefficients for the past three sunspot cycles.
The interplay between the various modes is then interpreted from the
perspective of general dynamo theory, where the coupling between the primary
and secondary families of modes is found to correlate with large-scale polarity
reversals for many examples of cyclic dynamos. Mean-field dynamos based on the
solar parameter regime are then used to explore how such couplings may result
in the various long-term trends in the surface magnetic field observed to occur
in the solar case.Comment: Accepted to ApJ; comments/corrections to this article are welcome via
e-mail, even after publicatio

### Angular dependence of domain wall resistivity in SrRuO$_{{\bf 3}}$ films

${\rm SrRuO_3}$ is a 4d itinerant ferromagnet (T$_{c}$ $\sim$150 K) with
stripe domain structure. Using high-quality thin films of SrRuO$_{3}$ we study
the resistivity induced by its very narrow ($\sim 3$ nm) Bloch domain walls,
$\rho_{DW}$ (DWR), at temperatures between 2 K and T$_{c}$ as a function of the
angle, $\theta$, between the electric current and the ferromagnetic domains
walls. We find that $\rho_{DW}(T,\theta)=\sin^2\theta
\rho_{DW}(T,90)+B(\theta)\rho_{DW}(T,0)$ which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is $\sin^2\theta$. We expect magnetic multilayers to exhibit a similar
behavior.Comment: 5 pages, 5 figure

### Spin accumulation induced resistance in mesoscopic ferromagnet/ superconductor junctions

We present a description of spin-polarized transport in mesoscopic
ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and
the interfaces are transparent. It is shown that the spin reversal associated
with Andreev reflection generates an excess spin density close to the F/S
interface, which leads to a spin contact resistance. Expressions for the
contact resistance are given for two terminal and four terminal geometries. In
the latter the sign depends on the relative magnetization of the ferromagnetic
electrodes.Comment: RevTeX 10 pages, 4 figures, submitted to Phys.Rev. Let

### 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

- …