430 research outputs found
Current induced distortion of a magnetic domain wall
We consider the spin torque induced by a current flowing ballistically
through a magnetic domain wall. In addition to a global pressure in the
direction of the electronic flow, the torque has an internal structure of
comparable magnitude due to the precession of the electrons' spins at the
"Larmor" frequency. As a result, the profile of the domain wall is expected to
get distorted by the current and acquires a periodic sur-structure.Comment: 5 pages, 3 eps figure
Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy
The time and field dependence of the magnetic domain structure at
magnetization reversal were investigated by Kerr microscopy in interacting
ferromagnetic Co/Pt multilayers with perpendicular anisotropy. Large local
inhomogeneous magnetostatic fields favor mirroring domain structures and domain
decoration by rings of opposite magnetization. The long range nature of these
magnetostatic interactions gives rise to ultra-slow dynamics even in zero
applied field, i.e. it affects the long time domain stability. Due to this
additionnal interaction field, the magnetization reversal under short magnetic
field pulses differs markedly from the well-known slow dynamic behavior.
Namely, in high field, the magnetization of the coupled harder layer has been
observed to reverse more rapidly by domain wall motion than the softer layer
alone.Comment: 42 pages including 17 figures. submitted to JA
Diagnostic des systèmes techniques de transformation de l'igname en cossettes séchées au Bénin
Les pertes après-récolte des tubercules d'igname enregistrées dans les pays producteurs de l'Afrique de l'Ouest sont très importantes (40-50 % après 6 mois de stockage). Ces pertes sont dues à l'absence de moyens et méthodes de conservation appropriés. La transformation des tubercules en produits stables (cossettes, farine) est une solution à la conservation de l'igname frais. Cette technique permet, en outre, de réduire de plus de la moitié le poids de la matière à transporter. La méthode de fabrication des cossettes d'igname, connue depuis longtemps au Bénin et dans les pays voisins (Nigeria, Togo), permet de conserver le surplus des tubercules pour les utiliser pendant les périodes de soudure. Depuis plus d'une décennie, la farine de cossettes d'igname (Elubo) est passée dans les habitudes alimentaires des populations urbaines. L'importance de la demande actuelle nécessite que cette technique soit évaluée, améliorée et valorisée
The role des ports de la Communaute pour le trafic de cereales et de farines. XI. Monographies pour les principaux ports de la Belgique = The role of Community ports for the trade of cereals and flours. XI. Monographs for the principal ports of Belgium. Internal information on agriculture 159, August 1975. VI/3174/75-F
Magnetic patterning of (Ga,Mn)As by hydrogen passivation
We present an original method to magnetically pattern thin layers of
(Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the
hole density, and thereby locally suppress the carrier-mediated ferromagnetic
phase. The sample surface is thus maintained continuous, and the minimal
structure size is of about 200 nm. In micron-sized ferromagnetic dots
fabricated by hydrogen passivation on perpendicularly magnetized layers, the
switching fields can be maintained closer to the continuous film coercivity,
compared to dots made by usual dry etch techniques
Current Induced Fingering Instability in Magnetic Domain Walls
The shape instability of magnetic domain walls under current is investigated
in a ferromagnetic (Ga,Mn)(As,P) film with perpendicular anisotropy. Domain
wall motion is driven by the spin transfer torque mechanism. A current density
gradient is found either to stabilize domains with walls perpendicular to
current lines or to produce finger-like patterns, depending on the domain wall
motion direction. The instability mechanism is shown to result from the
non-adiabatic contribution of the spin transfer torque mechanism.Comment: 5 pages, 3 figures + supplementary material
Theory of Current-Driven Domain Wall Motion: A Poorman's Approach
A self-contained theory of the domain wall dynamics in ferromagnets under
finite electric current is presented.
The current is shown to have two effects; one is momentum transfer, which is
proportional to the charge current and wall resistivity (\rhow), and the
other is spin transfer, proportional to spin current.
For thick walls, as in metallic wires, the latter dominates and the threshold
current for wall motion is determined by the hard-axis magnetic anisotropy,
except for the case of very strong pinning.
For thin walls, as in nanocontacts and magnetic semiconductors, the
momentum-transfer effect dominates, and the threshold current is proportional
to \Vz/\rhow, \Vz being the pinning potential
Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy
The ferromagnetism of a thin GaMnAs layer with a perpendicular easy
anisotropy axis is investigated by means of several techniques, that yield a
consistent set of data on the magnetic properties and the domain structure of
this diluted ferromagnetic semiconductor. The magnetic layer was grown under
tensile strain on a relaxed GaInAs buffer layer using a procedure that limits
the density of threading dislocations. Magnetometry, magneto-transport and
polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality
of this layer, in particular through its high Curie temperature (130 K) and
well-defined magnetic anisotropy. We show that magnetization reversal is
initiated from a limited number of nucleation centers and develops by easy
domain wall propagation. Furthermore, MOKE microscopy allowed us to
characterize in detail the magnetic domain structure. In particular we show
that domain shape and wall motion are very sensitive to some defects, which
prevents a periodic arrangement of the domains. We ascribed these defects to
threading dislocations emerging in the magnetic layer, inherent to the growth
mode on a relaxed buffer
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