100 research outputs found
Optimizing magneto-dipolar interactions for synchronizing vortex based spin-torque nano-oscillators
We report on a theoretical study about the magneto-dipolar coupling and
synchronization between two vortex-based spin-torque nano-oscillators. In this
work we study the dependence of the coupling efficiency on the relative
magnetization parameters of the vortices in the system. For that purpose, we
combine micromagnetic simulations, Thiele equation approach, and analytical
macro-dipole approximation model to identify the optimized configuration for
achieving phase-locking between neighboring oscillators. Notably, we compare
vortices configurations with parallel (P) polarities and with opposite (AP)
polarities. We demonstrate that the AP core configuration exhibits a coupling
strength about three times larger than in the P core configuration.Comment: 8 pages, 11 figure
Phase locking dynamics of dipolarly coupled vortex-based spin transfer oscillators
Phase locking dynamics of dipolarly coupled vortices excited by
spin-polarized current in two identical nanopillars is studied as a function of
the interpillar distance L. Numerical study and analytical model have proved
the remarkable efficiency of magneto-static interaction to achieve phase
locking. Investigating the dynamics in the transient regime towards phase
locking, we extract the evolution of the locking time \tau, the coupling
strength {\mu} and the interaction energy W. Finally, we compare this coupling
energy with the one obtained by simple model.Comment: 4 pages, 4 figure
Field dependence of magnetization reversal by spin transfer
We analyse the effect of the applied field (Happl) on the current-driven
magnetization reversal in pillar-shaped Co/Cu/Co trilayers, where we observe
two different types of transition between the parallel (P) and antiparallel
(AP) magnetic configurations of the Co layers. If Happl is weaker than a rather
small threshold value, the transitions between P and AP are irreversible and
relatively sharp. For Happl exceding the threshold value, the same transitions
are progressive and reversible. We show that the criteria for the stability of
the P and AP states and the experimentally observed behavior can be precisely
accounted for by introducing the current-induced torque of the spin transfer
models in a Landau-Lifschitz-Gilbert equation. This approach also provides a
good description for the field dependence of the critical currents
Microwave neural processing and broadcasting with spintronic nano-oscillators
Can we build small neuromorphic chips capable of training deep networks with
billions of parameters? This challenge requires hardware neurons and synapses
with nanometric dimensions, which can be individually tuned, and densely
connected. While nanosynaptic devices have been pursued actively in recent
years, much less has been done on nanoscale artificial neurons. In this paper,
we show that spintronic nano-oscillators are promising to implement analog
hardware neurons that can be densely interconnected through electromagnetic
signals. We show how spintronic oscillators maps the requirements of artificial
neurons. We then show experimentally how an ensemble of four coupled
oscillators can learn to classify all twelve American vowels, realizing the
most complicated tasks performed by nanoscale neurons
Magnetic domain wall motion by spin transfer
The discovery that a spin polarized current can exert a large torque on a
ferromagnet through a transfusion of spin angular momentum, offers a new way to
control a magnetization by simple current injection, without the help of an
applied external field. Spin transfer can be used to induce magnetization
reversals and oscillations, or to control the position of a magnetic domain
wall. In this review, we focus on this last mechanism, which is today the
subject of an extensive research, both because the microscopic details for its
origin are still debated, but also because promising applications are at stake
for non-volatile magnetic memories
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
Microwave excitations associated with a wavy angular dependence of the spin transfer torque : model and experiments
The spin transfer torque (STT) can lead to steady precession of magnetization
without any external applied field in magnetic spin valve where the magnetic
layer have very different spin diffusion length. This effect is associated with
an unusual angular dependence of the STT, called "wavy" (WAD-STT), predicted in
the frame of diffusive models of spin transfer. In this article, we present a
complete experimental characterization of the magnetization dynamics in the
presence of a WAD-STT. The results are compared to the prediction of the
magnetization dynamics obtained by single domain magnetic simulations
(macrospin approximation). The macrospin simulations well reproduced the main
static and dynamical experimental features (phase diagram, R(I) curves,
dependence of frequency with current and field) and suggest that the dynamical
excitations observed experimentally are associated with a large angle
out-of-plane precession mode. The present work validates the diffusive models
of the spin transfer and underlines the role of the spin accumulation and the
spin relaxation effects on the STT
The NIKA2 instrument, a dual-band kilopixel KID array for millimetric astronomy
NIKA2 (New IRAM KID Array 2) is a camera dedicated to millimeter wave
astronomy based upon kilopixel arrays of Kinetic Inductance Detectors (KID).
The pathfinder instrument, NIKA, has already shown state-of-the-art detector
performance. NIKA2 builds upon this experience but goes one step further,
increasing the total pixel count by a factor 10 while maintaining the
same per pixel performance. For the next decade, this camera will be the
resident photometric instrument of the Institut de Radio Astronomie
Millimetrique (IRAM) 30m telescope in Sierra Nevada (Spain). In this paper we
give an overview of the main components of NIKA2, and describe the achieved
detector performance. The camera has been permanently installed at the IRAM 30m
telescope in October 2015. It will be made accessible to the scientific
community at the end of 2016, after a one-year commissioning period. When this
happens, NIKA2 will become a fundamental tool for astronomers worldwide.Comment: Proceedings of the 16th Low Temperature Detectors workshop. To be
published in the Journal of Low Temperature Physics. 8 pages, 4 figures, 1
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