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2020-10-14
|
Spin torque gate magnetic field sensor
|
Spin-orbit torque provides an efficient pathway to manipulate the magnetic
state and magnetization dynamics of magnetic materials, which is crucial for
energy-efficient operation of a variety of spintronic devices such as magnetic
memory, logic, oscillator, and neuromorphic computing. Here, we describe and
experimentally demonstrate a strategy for the realization of a spin torque gate
magnetic field sensor with extremely simple structure by exploiting the
longitudinal field dependence of the spin torque driven magnetization
switching. Unlike most magnetoresistance sensors which require a delicate
magnetic bias to achieve a linear response to the external field, the spin
torque gate sensor can achieve the same without any magnetic bias, which
greatly simplifies the sensor structure. Furthermore, by driving the sensor
using an ac current, the dc offset is automatically suppressed, which
eliminates the need for a bridge or compensation circuit. We verify the concept
using the newly developed WTe2/Ti/CoFeB trilayer and demonstrate that the
sensor can work linearly in the range of 3-10 Oe with negligible dc offset.
|
2010.07158v1
|
2020-11-06
|
Picosecond Switching of Optomagnetic Tunnel Junctions
|
Perpendicular magnetic tunnel junctions are one of the building blocks for
spintronic memories, which allow fast nonvolatile data access, offering
substantial potentials to revolutionize the mainstream computing architecture.
However, conventional switching mechanisms of such devices are fundamentally
hindered by spin polarized currents4, either spin transfer torque or spin orbit
torque with spin precession time limitation and excessive power dissipation.
These physical constraints significantly stimulate the advancement of modern
spintronics. Here, we report an optomagnetic tunnel junction using a
spintronic-photonic combination. This composite device incorporates an
all-optically switchable Co/Gd bilayer coupled to a CoFeB/MgO-based
perpendicular magnetic tunnel junction by the Ruderman-Kittel-Kasuya-Yosida
interaction. A picosecond all-optical operation of the optomagnetic tunnel
junction is explicitly confirmed by time-resolved measurements. Moreover, the
device shows a considerable tunnel magnetoresistance and thermal stability.
This proof-of-concept device represents an essential step towards ultrafast
spintronic memories with THz data access, as well as ultralow power
consumption.
|
2011.03612v1
|
2020-12-10
|
Observation of Magnetic Droplets in Magnetic Tunnel Junctions
|
Magnetic droplets, a class of highly non-linear magnetodynamical solitons,
can be nucleated and stabilized in nanocontact spin-torque nano-oscillators
where they greatly increase the microwave output power. Here, we experimentally
demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet
nucleation is accompanied by a power increase of over 300 times compared to its
ferromagnetic resonance modes. The nucleation and stabilization of droplets are
ascribed to the double-CoFeB free layer structure in the all-perpendicular MTJ
which provides a low Zhang-Li torque and a high pinning field. Our results
enable better electrical sensitivity in the fundamental studies of droplets and
show that the droplets can be utilized in MTJ-based applications.
|
2012.05596v1
|
2020-12-20
|
Creation of a Chiral Bobber Lattice in Helimagnet-Multilayer Heterostructures
|
A chiral bobber is a localized three-dimensional magnetization configuration,
terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in
chiral magnets, lending themselves to new types of skyrmion-complementary bits
of information. However, the on-demand creation of bobbers, as well as their
direct observation remained elusive. Here, we introduce a new mechanism for
creating a stable chiral bobber lattice state via the proximity of two skyrmion
species with comparable size. This effect is experimentally demonstrated in a
Cu$_2$OSeO$_3$/[Ta/CoFeB/MgO]$_4$ heterostructure in which an exotic bobber
lattice state emerges in the phase diagram of Cu$_2$OSeO$_3$. To unambiguously
reveal the existence of the chiral bobber lattice state, we have developed a
novel characterization technique, magnetic truncation rod analysis, which is
based on resonant elastic x-ray scattering.
|
2012.10924v1
|
2021-01-10
|
A Thermodynamic Core using Voltage-Controlled Spin-Orbit-Torque Magnetic Tunnel Junctions
|
We present a magnetic implementation of a thermodynamic computing fabric.
Magnetic devices within computing cores harness thermodynamics through its
voltage-controlled thermal stability; while the evolution of network states is
guided by the spin-orbit-torque effect. We theoretically derive the dynamics of
the cores and show that the computing fabric can successfully compute ground
states of a Boltzmann Machine. Subsequently, we demonstrate the physical
realization of these devices based on a CoFeB-MgO magnetic tunnel junction
structure. The results of this work pave the path towards the realization of
highly efficient, high-performance thermodynamic computing hardware. Finally,
this paper will also give a perspective of computing beyond thermodynamic
computing.
|
2101.03448v3
|
2021-04-07
|
Magnetic Reversal and Critical Current Transparency of CoFeB Superconductor-Ferromagnet-Superconductor Heterostructures
|
In this work, we show fundamental low temperature (T) magnetic and Ic
responses of a magnetic Josephson Junction (MJJ) S/F/S heterostructure - Nb/
Co56Fe24B20 /Nb. The ultra-thin Co56Fe24B20 (CFB) films (0.6-1.3 nm) were
deposited onto two separate buffer layers: 150 nm Nb/5 nm Cu and 150 nm Nb/ (1
nm Cu/0.5 nm Nb)6/1 nm Cu. Both film sets were capped with 5 nm Cu/50 nm Nb.
Magnetic results show reduced switching distributions in patterned arrays
measured at near liquid Helium temperature (~ 10 K), with the incorporation of
the (1 nm Cu/0.5 nm Nb)6/1 nm multilayer. In electrical devices, the critical
current (Ic) through the CFB layer decays exponentially with increasing
ferromagnetic layer thickness and shows a dip in Ic at 0.8 nm, characteristic
of a change in the equilibrium Josephson phase in an S/F/S structure.
|
2104.03188v1
|
2021-06-22
|
Room And Cryogenic Temperature Behaviour of Magnetic Sensors Based on Gan/Si Single Saw Resonators
|
This work analyzes resonance frequency shift vs. the applied magnetic field
strength for GHz operating GaN/Si SAW single resonators. Magnetostrictive
elements (Ni and CoFeB) were deposited in the proximity of the interdigitated
transducers (IDTs) of the resonators (A-type structures) and also over the
IDTs, after covering them with a BCB layer to avoid short circuits with IDTs
metal (B-type structures). This work targets emerging applications of SAW
resonators in driving spin wave pumping and in coupling of surface acoustic
waves (SAW) with superconducting Q-bits. Magnetic sensitivity of the SAWs was
analyzed at room temperature (RT) and at cryogenic temperatures, obtaining high
magnetic sensitivities at 16 K. According to our knowledge, GaN based SAWs are
first time used in magnetic applications; also, cryogenic behavior of magnetic
SAW sensors is first time analyzed.
|
2106.11605v1
|
2021-08-01
|
Terahertz charge and spin transport in metallic ferromagnets: the role of crystalline and magnetic order
|
We study the charge and spin dependent scattering in a set of CoFeB thin
films whose crystalline order is systematically enhanced and controlled by
annealing at increasingly higher temperatures. Terahertz conductivity
measurements reveal that charge transport closely follows the development of
the crystalline phase, with increasing structural order leading to higher
conductivity. The terahertz-induced ultrafast demagnetization, driven by
spin-flip scattering mediated by the spin-orbit interaction, is measurable in
the pristine amorphous sample and much reduced in the sample with highest
crystalline order. Surprisingly, the largest demagnetization is observed at
intermediate annealing temperatures, where the enhancement in spin-flip
probability is not associated with an increased charge scattering. We are able
to correlate the demagnetization amplitude with the magnitude of the in-plane
magnetic anisotropy, which we characterize independently, suggesting a
magnetoresistance-like description of the phenomenon.
|
2108.00456v1
|
2021-11-12
|
Fabrication of voltage gated spin Hall nano-oscillators
|
We demonstrate an optimized fabrication process for electric field (voltage
gate) controlled nano-constriction spin Hall nano-oscillators (SHNOs),
achieving feature sizes of <30 nm with easy to handle ma-N 2401 e-beam
lithography negative tone resist. For the nanoscopic voltage gates, we utilize
a two-step tilted ion beam etching approach and through-hole encapsulation
using 30 nm HfO<sub>x</sub>. The optimized tilted etching process reduces
sidewalls by 75% compared to no tilting. Moreover, the HfO<sub>x</sub>
encapsulation avoids any sidewall shunting and improves gate breakdown. Our
experimental results on W/CoFeB/MgO/SiO<sub>2</sub> SHNOs show significant
frequency tunability (6 MHz/V) even for moderate perpendicular magnetic
anisotropy. Circular patterns with diameter of 45 nm are achieved with an
aspect ratio better than 0.85 for 80% of the population. The optimized
fabrication process allows incorporating a large number of individual gates to
interface to SHNO arrays for unconventional computing and densely packed
spintronic neural networks.
|
2111.06957v1
|
2021-11-26
|
Three-dimensional Resonant Magnetization Dynamics Unraveled by Time-Resolved Soft X-ray Laminography
|
The imaging of magneto-dynamical processes has been, so far, mostly a
two-dimensional business, due to the constraints of the available experimental
techniques. In this manuscript, building on the recent developments of soft
X-ray magnetic laminography, we present an experimental setup where
magneto-dynamical processes can be resolved in all three spatial dimensions and
in time, with the possibility to freely tune the frequency of the dynamical
process. We then employ this setup to investigate the three-dimensional
dynamics of two resonant magneto-dynamical modes in a CoFeB microstructure
occurring at different frequencies, namely the fundamental vortex gyration mode
and a magnetic field-induced domain wall excitation mode. This new technique
provides much needed capabilities for the experimental investigation of the
magnetization dynamics of three-dimensional magnetic systems.
|
2111.13533v1
|
2022-01-11
|
Perpendicular magnetic tunnel junctions with multi-interface free layer
|
Future generations of magnetic random access memory demand magnetic tunnel
junctions that can provide simultaneously high magnetoresistance, strong
retention, low switching energy and small cell size below 10nm. Here we study
perpendicular magnetic tunnel junctions with composite free layers where
multiple ferromagnet/nonmagnet interfaces can contribute to the thermal
stability. Different nonmagnetic materials (MgO, Ta, Mo) have been employed as
the coupling layers in these multi-interface free layers. The evolution of
junction properties under different annealing conditions is investigated. A
strong dependence of tunneling magnetoresistance on the thickness of the first
CoFeB layer has been observed. In junctions where Mo and MgO are used as
coupling layers, large tunneling magnetoresistance above 200% has been achieved
after 400{\deg}C annealing.
|
2201.03798v1
|
2022-04-06
|
Power transfer in magnetoelectric resonators
|
We derive an analytical model for the power transfer in a magnetoelectric
film bulk acoustic resonator consisting of a piezoelectric--magnetostrictive
bilayer. The model describes the dynamic magnetostrictive influence on the
elastodynamics via an effective frequency-dependent stiffness constant. This
allows for the calculation of both the magnetic and elastic power absorption in
the resonator as well as of its energy efficiency when such a resonator is
considered as a magnetic transducer. The model is then applied to example
systems consisting of piezoelectric ScAlN and magnetostrictive CoFeB, Ni, or
Terfenol-D layers.
|
2204.03072v2
|
2022-10-03
|
Voltage control of frequency, effective damping and threshold current in nano-constriction-based spin Hall nano-oscillators
|
Using micromagnetic simulations, we study the interplay between strongly
voltage-controlled magnetic anisotropy (VCMA), $\Delta K = \pm$200 kJ/m$^3$,
and gate width, $w=$ 10--400 nm, in voltage-gated W/CoFeB/MgO based
nano-constriction spin Hall nano-oscillators. The VCMA modifies the local
magnetic properties such that the magnetodynamics transitions between regimes
of \emph{i}) confinement, \emph{ii}) tuning, and \emph{iii}) separation, with
qualitatively different behavior. We find that the strongest tuning is achieved
for gate widths of the same size as the the constriction width, for which the
effective damping can be increased an order of magnitude compared to its
intrinsic value. As a consequence, voltage control remains efficient over a
very large frequency range, and subsequent manufacturing advances could allow
SHNOs to be easily integrated into next-generation electronics for further
fundamental studies and industrial applications.
|
2210.01042v1
|
2022-10-11
|
Thermally-generated spin current in the topological insulator Bi$_2$Se$_3$
|
We complete measurements of interconversions among the full triad of thermal
gradients, charge currents, and spin currents in the topological insulator
Bi$_2$Se$_3$ by quantifying the efficiency with which thermal gradients can
generate transverse spin currents. We accomplish this by comparing the spin
Nernst magneto-thermopower to the spin Hall magnesistance for bilayers of
Bi$_2$Se$_3$/CoFeB. We find that Bi$_2$Se$_3$ does generate substantial
thermally-driven spin currents. A lower bound for the ratio of spin current to
thermal gradient is $J_s/\nabla_x T$ = (4.9 $\pm$ 0.9) $\times$ 10$^{6}$
($\hbar/2e$) A m$^{-2}$ / K $\mu$m$^{-1}$, and a lower bound for the magnitude
of the spin Nernst ratio is $-$0.61 $\pm$ 0.11. The spin Nernst ratio for
Bi$_2$Se$_3$ is the largest among all materials measured to date, 2-3 times
larger compared to previous measurements for the heavy metals Pt and W.
|
2210.05636v1
|
2022-10-26
|
Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers
|
Nb and its compounds are widely used in quantum computing due to their high
superconducting transition temperatures and high critical fields. Devices that
combine superconducting performance and spintronic non-volatility could deliver
unique functionality. Here we report the study of magnetic tunnel junctions
with Nb as the heavy metal layers. An interfacial perpendicular magnetic
anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO
heterostructures. The tunneling magnetoresistance was evaluated in junctions
with different thickness combinations and different annealing conditions. An
optimized magnetoresistance of 120% was obtained at room temperature, with a
damping parameter of 0.011 determined by ferromagnetic resonance. In addition,
spin-transfer torque switching has also been successfully observed in these
junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.
|
2210.14969v1
|
2022-10-30
|
Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions
|
The interfacial oxidation level and thermodynamic properties of the MgO-based
perpendicular magnetic tunneling junctions are investigated. The
symmetry-conserved tunneling effect depends sensitively on the MgO adatom
energy during the RF sputtering, as well as the thermal stability of the
structure during the post-growth thermal annealing. Two different failure modes
of the magnetoresistance are highlighted, involving with the decay of
perpendicular magnetic anisotropy and destruction of coherent tunneling
channels, respectively. Through the careful control of interfacial oxidation
level and proper selection of the heavy metal layers, both perpendicular
magnetic anisotropy and tunneling magnetoresistance of the junctions can be
increased.
|
2210.16734v1
|
2022-12-08
|
Acoustic-Driven Magnetic Skyrmion Motion
|
Magnetic skyrmions have great potential for developing novel spintronic
devices. The electrical manipulation of skyrmions has mainly relied on
current-induced spin-orbit torques. A recent theoretical model suggested that
the skyrmions could be more efficiently manipulated by surface acoustic waves
(SAW), an elastic wave that can couple with magnetic moment through
magnetoelastic effect. However, the directional motion of skyrmions that is
driven by SAW is still missing. Here, we experimentally demonstrate the motion
of N\'eel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers driven by propagating
SAW pulses from on-chip piezoelectric transducers. Our results reveal that the
elastic wave with longitudinal and shear vertical displacements (Rayleigh wave)
traps skyrmions, while the shear horizontal wave effectively drives the motion
of skyrmions. In particular, a longitudinal motion along the SAW propagation
direction and a transverse motion due to topological charge, are observed and
further confirmed by our micromagnetic simulations. This work demonstrates a
promising approach based on acoustic waves for manipulating skyrmions, which
could offer new opportunities for ultra-low power spintronics.
|
2212.04049v1
|
2023-04-30
|
Specific features of g $\approx$ 4.3 EPR line behavior in magnetic nanogranular composites
|
Films of metal-insulator nanogranular composites M$_x$D$_{100-x}$ with
different composition and percentage of metal and dielectric phases (M = Fe,
Co, CoFeB; D = Al$_2$O$_3$, SiO$_2$, LiNbO$_3$; x $\approx$ 15-70 at.%) are
investigated by magnetic resonance in a wide range of frequencies (f = 7-37
GHz) and temperatures (T = 4.2-360 K). In addition to the usual ferromagnetic
resonance signal from an array of nanogranules, the experimental spectra
contain an additional absorption peak, which we associate with the electron
paramagnetic resonance (EPR) of Fe and Co ions dispersed in the insulating
space between the granules. In contrast to the traditional EPR of Fe and Co
ions in weakly doped non-magnetic matrices, the observed peak demonstrates a
number of unusual properties, which we explain by the presence of magnetic
interactions between ions and granules.
|
2305.00551v1
|
2023-05-16
|
Terahertz spin conductance probes of coherent and incoherent spin tunneling through MgO tunnel junctions
|
We study femtosecond spin currents through MgO tunneling barriers in CoFeB(2
nm)|MgO($d$)|Pt(2 nm) stacks by terahertz emission spectroscopy. To obtain
transport information independent of extrinsic experimental factors, we
determine the complex-valued spin conductance $\tilde{G}_d (\omega)$ of the MgO
layer (thickness d= 0-6 {\AA} over a wide frequency range $(\omega/2\pi=$ 0.5-8
THz). In the time $(t)$ domain,$ G_d (t)$ has an instantaneous and delayed
component that point to (i) spin transport through Pt pinholes in MgO, (ii)
coherent spin tunneling and (iii) incoherent resonant spin tunneling mediated
by defect states in MgO. A remarkable signature of (iii) is its relaxation time
that grows monotonically with $d$ to as much as 270 fs at $d= 6$ {\AA}, in full
agreement with an analytical model. Our results indicate that terahertz spin
conductance spectroscopy will yield new and relevant insights into ultrafast
spin transport for a wide range of materials.
|
2305.09074v2
|
2023-05-18
|
Observation and enhancement of room temperature bilinear magnetoelectric resistance in sputtered topological semimetal Pt3Sn
|
Topological semimetal materials have become a research hotspot due to their
intrinsic strong spin-orbit coupling which leads to large charge-to-spin
conversion efficiency and novel transport behaviors. In this work, we have
observed a bilinear magnetoelectric resistance (BMER) of up to 0.1 nm2A-1Oe-1
in a singlelayer of sputtered semimetal Pt3Sn at room temperature. Different
from previous observations, the value of BMER in sputtered Pt3Sn does not
change out-of-plane due to the polycrystalline nature of Pt3Sn. The observation
of BMER provides strong evidence of the existence of spin-momentum locking in
the sputtered polycrystalline Pt3Sn. By adding an adjacent CoFeB magnetic
layer, the BMER value of this bilayer system is doubled compared to the single
Pt3Sn layer. This work broadens the material system in BMER study, which paves
the way for the characterization of topological states and applications for
spin memory and logic devices.
|
2305.10720v2
|
2023-07-07
|
Orbitronics: Light-induced Orbit Currents in Terahertz Emission Experiments
|
Orbitronics is based on the use of orbit currents as information carriers. Up
to now, orbit currents were created from the conversion of charge or spin
currents, and inversely, they could be converted back to charge or spin
currents. Here we demonstrate that orbit currents can also be generated by
femtosecond light pulses on Ni. In multilayers associating Ni with oxides and
nonmagnetic metals such as Cu, we detect the orbit currents by their conversion
into charge currents and the resulting terahertz emission. We show that the
orbit currents extraordinarily predominate the light-induced spin currents in
Ni-based systems, whereas only spin currents can be detected with CoFeB-based
systems. In addition, the analysis of the time delays of the terahertz pulses
leads to relevant information on the velocity and propagation of orbit
carriers. Our finding of light-induced orbit currents and our observation of
their conversion into charge currents opens new avenues in orbitronics,
including the development of orbitronic terahertz devices.
|
2307.03490v1
|
2023-09-06
|
Shaping magnetization dynamics in a planar square dot by adjusting its surface anisotropy
|
A planar square dot is one of the simplest structures confined to three
dimensions. Despite its geometrical simplicity, the description of the spin
wave modes in this structure is not trivial due to the competition of dipolar
and exchange interactions. An additional factor that makes this description
challenging are the boundary conditions depend both on non-local dipolar
interactions and local surface parameters such as surface anisotropy. In the
presented work, we showed how the surface anisotropy applied at the lateral
faces of the dot can tune the frequency of fundamental mode in the planar CoFeB
dot, magnetized in an out-of-plane direction. Moreover, we analyzed the spin
wave profile of the fundamental mode and the corresponding dynamic stray field.
We showed that the asymmetric application of surface anisotropy produces an
asymmetric profile of dynamic stray field for square dot and can be used to
tailor inter-dot coupling. The calculations were performed with the use of the
finite-element method.
|
2309.02984v1
|
2023-09-22
|
Strongly Coupled Spin Waves and Surface Acoustic Waves at Room Temperature
|
Here, we report the observation of strong coupling between magnons and
surface acoustic wave (SAW) phonons in a thin CoFeB film constructed in an
on-chip SAW resonator by analyzing SAW phonon dispersion anticrossings. Our
device design provides the tunability of the film thickness with a fixed phonon
wavelength, which is a departure from the conventional approach in strong
magnon--phonon coupling research. We detect a monotonic increase in the
coupling strength by expanding the film thickness, which agrees with our
theoretical model. Our work offers a significant way to advance fundamental
research and the development of devices based on magnon--phonon hybrid
quasiparticles.
|
2309.12690v1
|
2023-10-20
|
Visualization of skyrmion-superconducting vortex pairs in a chiral magnet-superconductor heterostructure
|
Magnetic skyrmions, the topological states possessing chiral magnetic
structure with non-trivial topology, have been widely investigated as a
promising candidate for spintronic devices. They can also couple with
superconducting vortices to form skyrmion-vortex pairs, hosting Majorana zero
mode which is a potential candidate for topological quantum computering. A lot
of theoretical proposals have been put forward on constructing skyrmion-vortex
pairs in heterostructures of chiral magnet and superconductor. Nevertheless,
how to generate skyrmion-vortex pairs in a controllable way experimentally
remains a significant challenge. We have designed a heterostructure of chiral
magnet and superconductor [CoFeB/Ir/Ta]7/Nb in which zero field N\'eel-type
skyrmions can be stabilized and the superconducting vortices can couple with
the skyrmions when Nb is in the superconducting state. We have directly
observed the formation of skyrmion-superconducting vortex pairs which is
dependent on the direction of the applied magnetic field. Our results provide
an effective method to manipulate the quantum states of skyrmions with the help
of superconducting vortices, which can be used to explore the possible
existence of Majorana zero mode for future quantum computation.
|
2310.13363v1
|
2023-10-26
|
On-chip all-electrical determination of the magnetoelastic coupling constant of magnetic heterostructures
|
We have developed an approach to determine the magnetoelastic coupling
constant of magnetic layers in thin film heterostructures. The film is formed
on a piezoelectric substrate between two interdigital transducers (IDT), a
platform often used to construct a surface acoustic wave device. With the
substrate piezoelectricity, strain is induced into the film by applying a dc
voltage to the IDTs. The strain causes changes in the magnetization direction
of the magnetic layer, which is probed by measuring changes, if any, in the
transverse resistance of the heterostructure. We find the extracted
magnetoelastic coupling constant of the magnetic layer (CoFeB) depends on the
film stacking. Such change can be accounted for provided that the elastic
properties of the layers that constitute the heterostructures are taken into
account. The on-chip all-electrical approach described here provides a
versatile means to quantitatively assess the magnetoelastic coupling constant
of thin film heterostructures.
|
2310.17215v1
|
2023-12-06
|
Large Non-Volatile Frequency Tuning of Spin Hall Nano-Oscillators using Circular Memristive Nano-Gates
|
Spin Hall nano oscillators (SHNOs) are promising candidates for neuromorphic
computing due to their miniaturized dimensions, non-linearity, fast dynamics,
and ability to synchronize in long chains and arrays. However, tuning the
individual SHNOs in large chains/arrays, which is key to implementing synaptic
control, has remained a challenge. Here, we demonstrate circular memristive
nano-gates, both precisely aligned and shifted with respect to
nano-constriction SHNOs of W/CoFeB/HfOx, with increased quality of the device
tunability. Gating at the exact center of the nano-constriction region is found
to cause irreversible degradation to the oxide layer, resulting in a permanent
frequency shift of the auto-oscillating modes. As a remedy, gates shifted
outside of the immediate nano-constriction region can tune the frequency
dramatically (>200 MHz) without causing any permanent change to the
constriction region. Circular memristive nano-gates can, therefore, be used in
SHNO chains/arrays to manipulate the synchronization states precisely over
large networks of oscillators.
|
2312.03352v2
|
2008-05-16
|
The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner-Wohlfarth nanoparticles
|
We consider the influence of interparticle interaction on the magnetization
reversal in the oriented Stoner-Wohlfarth nanoparticles ensemble. To do so, we
solve a kinetic equation for the relaxation of the overall ensemble
magnetization to its equilibrium value in some effective mean field. Latter
field consists of external magnetic field and interaction mean field
proportional to the instantaneous value of above magnetization. We show that
the interparticle interaction influences the temperature dependence of a
coercive field. This influence manifests itself in the noticeable coercivity at
$T>T_{b}$ ($T_{b}$ is so-called blocking temperature). The above interaction
can also lead to a formation of the "superferromagnetic" state with correlated
directions of particle magnetic moments at $T>T_{b}$. This state possesses
coercivity if the overall magnetization has a component directed along the easy
axis of each particle. We have shown that the coercive field in the
"superferromagnetic" state does not depend on measuring time. This time
influences both $T_{b}$ and the temperature dependence of coercive field at
$T<T_{b}$. We corroborate our theoretical results by measurements on
nanogranular films (CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$ with concentration of
ferromagnetic particles close, but below percolation threshold.
|
0805.2463v3
|
2009-07-22
|
Quantized spin wave modes in magnetic tunnel junction nanopillars
|
We present an experimental and theoretical study of the magnetic field
dependence of the mode frequency of thermally excited spin waves in rectangular
shaped nanopillars of lateral sizes 60x100, 75x150, and 105x190 nm2, patterned
from MgO-based magnetic tunnel junctions. The spin wave frequencies were
measured using spectrally resolved electrical noise measurements. In all
spectra, several independent quantized spin wave modes have been observed and
could be identified as eigenexcitations of the free layer and of the synthetic
antiferromagnet of the junction. Using a theoretical approach based on the
diagonalization of the dynamical matrix of a system of three coupled, spatially
confined magnetic layers, we have modeled the spectra for the smallest pillar
and have extracted its material parameters. The magnetization and exchange
stiffness constant of the CoFeB free layer are thereby found to be
substantially reduced compared to the corresponding thin film values. Moreover,
we could infer that the pinning of the magnetization at the lateral boundaries
must be weak. Finally, the interlayer dipolar coupling between the free layer
and the synthetic antiferromagnet causes mode anticrossings with gap openings
up to 2 GHz. At low fields and in the larger pillars, there is clear evidence
for strong non-uniformities of the layer magnetizations. In particular, at zero
field the lowest mode is not the fundamental mode, but a mode most likely
localized near the layer edges.
|
0907.3792v2
|
2014-09-02
|
Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy
|
Spin orbit torque (SOT) provides an efficient way of generating spin current
that promises to significantly reduce the current required for switching
nanomagnets. However, an in-plane current generated SOT cannot
deterministically switch a perpendicularly polarized magnet due to symmetry
reasons. On the other hand, perpendicularly polarized magnets are preferred
over in-plane magnets for high-density data storage applications due to their
significantly larger thermal stability in ultra-scaled dimensions. Here we show
that it is possible switch a perpendicularly polarized magnet by SOT without
needing an external magnetic field. This is accomplished by engineering an
anisotropy in the magnets such that the magnetic easy axis slightly tilts away
from the film-normal. Such a tilted anisotropy breaks the symmetry of the
problem and makes it possible to switch the magnet deterministically. Using a
simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of
the magnetization by reversing the polarity of the applied current. This
demonstration presents a new approach for controlling nanomagnets with spin
orbit torque.
|
1409.0620v3
|
2015-10-13
|
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
|
Terahertz electromagnetic radiation is extremely useful for numerous
applications such as imaging and spectroscopy. Therefore, it is highly
desirable to have an efficient table-top emitter covering the 1-to-30-THz
window whilst being driven by a low-cost, low-power femtosecond laser
oscillator. So far, all solid-state emitters solely exploit physics related to
the electron charge and deliver emission spectra with substantial gaps. Here,
we take advantage of the electron spin to realize a conceptually new terahertz
source which relies on tailored fundamental spintronic and photonic phenomena
in magnetic metal multilayers: ultrafast photo-induced spin currents, the
inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an
analytical model, such spintronic route offers unique possibilities for
systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer
generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel
source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals
in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and
cost.
|
1510.03729v2
|
2016-07-22
|
The Spin Nernst effect in Tungsten
|
The spin Hall effect allows generation of spin current when charge current is
passed along materials with large spin orbit coupling. It has been recently
predicted that heat current in a non-magnetic metal can be converted into spin
current via a process referred to as the spin Nernst effect. Here we report the
observation of the spin Nernst effect in W. In W/CoFeB/MgO heterostructures, we
find changes in the longitudinal and transverse voltages with magnetic field
when temperature gradient is applied across the film. The field-dependence of
the voltage resembles that of the spin Hall magnetoresistance. A comparison of
the temperature gradient induced voltage and the spin Hall magnetoresistance
allows direct estimation of the spin Nernst angle. We find the spin Nernst
angle of W to be similar in magnitude but opposite in sign with its spin Hall
angle. Interestingly, under an open circuit condition, such sign difference
results in spin current generation larger than otherwise. These results
highlight the distinct characteristics of the spin Nernst and spin Hall
effects, providing pathways to explore materials with unique band structures
that may generate large spin current with high efficiency.
|
1607.06594v2
|
2017-09-08
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Observation of Magnetic Radial Vortex Nucleation in a Multilayer Stack with Tunable Anisotropy
|
Recently discovered exotic magnetic configurations, namely magnetic solitons
appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya
Interaction (i-DMI), have excited scientists to explore their potential
applications in emerging spintronic technologies such as race-track magnetic
memory, spin logic, radio frequency nano-oscillators and sensors. Such studies
are motivated by their foreseeable advantages over conventional micro-magnetic
structures due to their small size, topological stability and easy spin-torque
driven manipulation with much lower threshold current densities giving way to
improved storage capacity, and faster operation with efficient use of energy.
In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers
by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane)
via interface engineering and postproduction treatments, we can stabilize a
variety of magnetic configurations such as N\'eel skyrmions, horseshoes and
most importantly for the first time, the recently predicted isolated radial
vortices at room temperature and under zero bias field. Especially, the radial
vortex state with its absolute convergence to or divergence from a single point
can potentially offer exciting new applications such as particle
trapping/detrapping in addition to magnetoresistive memories with efficient
switching, where the radial vortex state can act as a source of spin-polarized
current with radial polarization.
|
1709.02876v1
|
2018-03-12
|
Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field
|
The emission of circularly polarized light from a single quantum dot relies
on the injection of carriers with well-defined spin polarization. Here we
demonstrate single dot electroluminescence (EL) with a circular polarization
degree up to 35% at zero applied magnetic field. The injection of spin
polarized electrons is achieved by combining ultrathin CoFeB electrodes on top
of a spin-LED device with p-type InGaAs quantum dots in the active region. We
measure an Overhauser shift of several $\mu$eV at zero magnetic field for the
positively charged exciton (trion X$^+$) EL emission, which changes sign as we
reverse the injected electron spin orientation. This is a signature of dynamic
polarization of the nuclear spins in the quantum dot induced by the hyperfine
interaction with the electrically injected electron spin. This study paves the
way for electrical control of nuclear spin polarization in a single quantum dot
without any external magnetic field.
|
1803.04309v1
|
2018-06-20
|
Current-induced modulation of interfacial Dzyaloshinskii-Moriya interaction
|
The Dzyaloshinskii-Moriya (DM) interaction is an antisymmetric exchange
interaction that is responsible for the emergence of chiral magnetism. The
origin of the DM interaction, however, remains to be identified albeit the
large number of studies reported on related effects. It has been recently
suggested that the DM interaction is equivalent to an equilibrium spin current
density originating from spin-orbit coupling, an effect referred to as the spin
Doppler effect. The model predicts that the DM interaction can be controlled by
spin current injected externally. Here we show that the DM exchange constant
($D$) in W/CoFeB based heterostructures can be modulated with external current
passed along the film plane. At higher current, $D$ decreases with increasing
current, which we infer is partly due to the adiabatic spin transfer torque. At
lower current, $D$ increases linearly with current regardless of the polarity
of current flow. The rate of increase in $D$ with the current density agrees
with that predicted by the model based on the spin Doppler effect. These
results imply that the DM interaction at the HM/FM interface partly originates
from an equilibrium interface spin (polarized) current which can be modulated
externally.
|
1806.07746v2
|
2018-06-25
|
Two-terminal spin-orbit torque magnetoresistive random access memory
|
Spin-transfer torque magnetoresistive random access memory (STT-MRAM) is an
attractive alternative to current random access memory technologies due to its
non-volatility, fast operation and high endurance. STT-MRAM does though have
limitations including the stochastic nature of the STT-switching and a high
critical switching current, which makes it unsuitable for ultrafast operation
at nanosecond and sub-nanosecond regimes. Spin-orbit torque (SOT) switching,
which relies on the torque generated by an in-plane current, has the potential
to overcome these limitations. However, SOT-MRAM cells studied so far use a
three-terminal structure in order to apply the in-plane current, which
increases the size of the cells. Here we report a two-terminal SOT-MRAM cell
based on a CoFeB/MgO magnetic tunnel junction pillar on an ultrathin and narrow
Ta underlayer. In this device, an in-plane and out-of-plane current are
simultaneously generated upon application of a voltage, and we demonstrate that
the switching mechanism is dominated by SOT. We also compare our device to a
STT-MRAM cell built with the same architecture and show that critical write
current in the SOT-MRAM cell is reduced by more than 70%.
|
1806.09713v2
|
2018-09-14
|
Femtosecond control of terahertz spin-charge conversion in ferromagnetic heterostructures
|
Employing electron spin instead of charge to develop spintronic devices holds
the merits of low-power consumption in information technologies. Meanwhile, the
demand for increasing speed in spintronics beyond current CMOS technology has
further triggered intensive researches for ultrafast control of spins even up
to unprecedent terahertz regime. The femtosecond laser has been emerging as a
potential technique to generate an ultrafast spin-current burst for
magnetization manipulation. However, there is a great challenge to establish
all-optical control and monitor of the femtosecond transient spin current. Deep
insights into the physics and mechanism are extremely essential for the
technique. Here, we demonstrate coherently nonthermal excitation of femtosecond
spin-charge current conversion parallel to the magnetization in W/CoFeB/Pt
heterostructures driven by linearly polarized femtosecond laser pulses. Through
systematical investigation we observe the terahertz emission polarization
depends on both the magnetization direction and structural asymmetry. We
attribute this phenomenon of the terahertz generation parallel to the
magnetization induced by linearly polarized femtosecond laser pulses probably
to inverse spin-orbit torque effect. Our work not only is beneficial to the
deep understanding of spin-charge conversion and spin transportation, but also
helps develop novel on-chip terahertz opto-spintronic devices.
|
1809.05391v2
|
2018-11-21
|
Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition-Metal Dichalcogenide/Ferromagnet Bilayers
|
The electronic and optoelectronic properties of two dimensional materials
have been extensively explored in graphene and layered transition metal
dichalcogenides (TMDs). Spintronics in these two-dimensional materials could
provide novel opportunities for future electronics, for example, efficient
generation of spin current, which should enable the efficient manipulation of
magnetic elements. So far, the quantitative determination of charge current
induced spin current and spin-orbit torques (SOTs) on the magnetic layer
adjacent to two-dimensional materials is still lacking. Here, we report a large
SOT generated by current-induced spin accumulation through the Rashba-Edelstein
effect in the composites of monolayer TMD (MoS$_2$ or WSe$_2$)/CoFeB bilayer.
The effective spin conductivity corresponding to the SOT turns out to be almost
temperature-independent. Our results suggest that the charge-spin conversion in
the chemical vapor deposition-grown large-scale monolayer TMDs could
potentially lead to high energy efficiency for magnetization reversal and
convenient device integration for future spintronics based on two-dimensional
materials.
|
1811.08583v1
|
2020-01-15
|
Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling
|
One of the most fundamental forms of magnon-phonon interaction is an
intrinsic property of magnetic materials, the "magnetoelastic coupling". This
particular form of interaction has been the basis for describing magnetic
materials and their strain related applications, where strain induces changes
of internal magnetic fields. Different from the magnetoelastic coupling, more
than 40 years ago, it was proposed that surface acoustic waves may induce
surface magnons via rotational motion of the lattice in anisotropic magnets.
However, a signature of this magnon-phonon coupling mechanism, termed
magneto-rotation coupling, has been elusive. Here, we report the first
observation and theoretical framework of the magneto-rotation coupling in a
perpendicularly anisotropic ultra-thin film Ta/CoFeB(1.6 nm)/MgO, which
consequently induces nonreciprocal acoustic wave attenuation with a
unprecedented ratio up to 100$\%$ rectification at the theoretically predicted
optimized condition. Our work not only experimentally demonstrates a
fundamentally new path for investigating magnon-phonon coupling, but also
justify the feasibility of the magneto-rotation coupling based application.
|
2001.05135v3
|
2020-01-15
|
Backward volume vs Damon-Eshbach: a travelling spin wave spectroscopy comparison
|
We compare the characteristics of electrically transduced Damon-Eshbach
(DESWs) and backward volume (BVSWs) configurations within the same, 30 nm
thick, ferromagnetic, CoFeB waveguide. Sub-micron U-shaped antennas are used to
deliver the necessary in-plane and out-of-plane RF fields. We measure the
spin-wave transmission with respect to in-plane field orientation, frequency
and propagation distance. Unlike DESW, BVSWs are reciprocally transduced and
collected for either direction of propagation, but their ability to transport
energy is lower than DESWs for two reasons. This arises first because BVSW are
inductively transduced less efficiently than DESWs. Also, in the range of
wavevectors (~5 rad. um-1) typically excited by our antennas, the group
velocity of BVSWs stays lower than that of DESW, which leads to reduced
propagation ability that impact transmission signals in an exponential manner.
In contrast, the group velocity of DESWs is maximum at low fields and decreases
continuously with the applied field. The essential features of the measured SW
characteristics are well reciprocated by a simple, 1-D analytical model which
can be used to assess the potential of each configuration.
|
2001.05221v2
|
2021-07-20
|
Spin-wave dispersion measurement by variable-gap propagating spin-wave spectroscopy
|
Magnonics is seen nowadays as a candidate technology for energy-efficient
data processing in classical and quantum systems. Pronounced nonlinearity,
anisotropy of dispersion relations and phase degree of freedom of spin waves
require advanced methodology for probing spin waves at room as well as at mK
temperatures. Yet, the use of the established optical techniques like Brillouin
light scattering (BLS) or magneto optical Kerr effect (MOKE) at ultra-low
temperatures is forbiddingly complicated. By contrast, microwave spectroscopy
can be used at all temperatures but is usually lacking spatial and wavenumber
resolution. Here, we develop a variable-gap propagating spin-wave spectroscopy
(VG-PSWS) method for the deduction of the dispersion relation of spin waves in
wide frequency and wavenumber range. The method is based on the phase-resolved
analysis of the spin-wave transmission between two antennas with variable
spacing, in conjunction with theoretical data treatment. We validate the method
for the in-plane magnetized CoFeB and YIG thin films in $k\perp B$ and
$k\parallel B$ geometries by deducing the full set of material and spin-wave
parameters, including spin-wave dispersion, hybridization of the fundamental
mode with the higher-order perpendicular standing spin-wave modes and surface
spin pinning. The compatibility of microwaves with low temperatures makes this
approach attractive for cryogenic magnonics at the nanoscale.
|
2107.09363v1
|
2017-03-18
|
Spin Based Biosensor with Hard Axis Assist for Enhanced Sensitivity
|
We demonstrate the influence of hard axis assist on an in-plane polarized
nanomagnet layer to greatly enhance the sensitivity of a magnetic nano particle
(MNP) based MTJ biosensor. The hard axis assist has been provided to the
sensing layer in the forms of spin Hall Effect (SHE) induced spin injected
torque and stress based effective magnetic field induced torque separately.
Present work mainly focuses on the efficient and qualitative detection of a
single magnetic bead with the aim of detecting a single bimolecular recognition
event at an extremely low analyte concentration. Interfacial spin current
arising from spin orbit metal is expected to impose a torque on the free layer
along sensitive direction improving the signal strength by a factor of ~ 6.5
for a 100 nm bead at a height of 500 nm above the sensor surface. Furthermore,
the potentiality of a multiferroic composite consisting of a piezoelectric
layer coupled with magnetostrictive CoFeB based MTJ has been investigated in
the Biosensing applications. An external stress voltage of 500 mV has been
observed to be sufficient to enhance the sensitivity (~ 6 times). The use of
nanoscaled spin devices and the absence of external magnetic field operated
magnetization rotation facilitates in achieving highly compact and extremely
low power designs. This establishes the possibility of utilizing the present
schemes for advanced, highly sensitive, miniaturized and low power bioassaying
system-on-chip applications. Numerical results were compared with some earlier
reported experimental results to validate our proposed model.
|
1704.01555v1
|
2017-04-20
|
Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves
|
We have investigated co-directional and contra-directional couplings between
spin wave and acoustic wave in one-dimensional periodic structure (magphonic
crystal). The system consists of two ferromagnetic layers alternating in space.
We have taken into consideration materials commonly used in magnonics: yttrium
iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
formalism have been successfully implemented to describe magnetoelastic
interaction as a periodic perturbation in the magphonic crystal. The results of
CMT calculations have been verified by more rigorous simulations by
frequency-domain plane wave method and time-domain finite element method. The
presented resonant coupling in the magphonic crystal is an active in-space
mechanism which spatially transfers energy between propagating spin and
acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
and design a spin wave - acoustic wave transducer based on a magphonic
crystals. The effect of spin wave damping has been included to the model to
discuss the efficiency of such a device. Our model shows that it is possible to
obtain forward conversion of the acoustic wave to the spin wave in case of
co-directional coupling and backward conversion in case of contra-directional
coupling.
|
1704.06118v1
|
2018-07-17
|
Large anomalous Nernst effect in thin films of the Weyl semimetal Co2MnGa
|
The magneto-thermoelectric properties of Heusler compound thin films are very
diverse. Here, we discuss the anomalous Nernst response of Co$_2$MnGa thin
films. We systematically study the anomalous Nernst coefficient as a function
of temperature, and we show that unlike the anomalous Hall effect, the
anomalous Nernst effect in Co$_2$MnGa strongly varies with temperature. We
exploit the on-chip thermometry technique to quantify the thermal gradient,
which enables us to directly evaluate the anomalous Nernst coefficient. We
compare these results to a reference CoFeB thin film. We show that the
50-nm-thick Co$_2$MnGa films exhibit a large anomalous Nernst effect of
-2$\mu$V/K at 300 K, whereas the 10-nm-thick Co$_2$MnGa film exhibits a
significantly smaller anomalous Nernst coefficient despite having similar
volume magnetizations. These findings suggest that the microscopic origin of
the anomalous Nernst effect in Co$_2$MnGa is complex and may contain
contributions from skew-scattering, side-jump or intrinsic Berry phase. In any
case, the large anomalous Nernst coefficent of Co$_2$MnGa thin films at room
temperature makes this material system a very promising candidate for efficient
spin-caloritronic devices.
|
1807.06487v1
|
2019-01-05
|
Demonstration of a strain-mediated magnetoelectric write and read unit in a Co60Fe20B20/ Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructure
|
Taking advantage of the Magnetoelectric (ME) and its inverse effect, this
article demonstrates strain-mediated magnetoelectric write and read operations
simultaneously in Co60Fe20B20/ Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures
without using any symmetry breaking magnetic field at room temperature. By
applying an external DC-voltage across a (011)-cut PMN-PT substrate, the
ferroelectric polarization is re-oriented, which results in an anisotropic
in-plane strain that transfers to the CoFeB thin film and changes its magnetic
anisotropy Hk. The change in Hk in-turn results in a 90o rotation of the
magnetic easy axis for sufficiently high voltages. Simultaneously, the inverse
effect is employed to read changes of the magnetic properties. Because the
Piezoelectric (PE)/FerroMagnetic (FM) system is fully coupled, the change of
magnetization in FM induces an elastic stress in the PE layer, which generates
a piezoelectric potential in the system that can be used to readout the
magnetic state of the FM layer. Our experimental results are in excellent
qualitative agreement with a recently proposed, experimentally benchmarked
equivalent circuit model that considers how magnetic properties are
electrically controlled in such ME/PE heterostructure and how a back-voltage is
generated due to changing magnetic properties in a self-consistent model.
|
1901.01368v1
|
2019-01-24
|
Topology-Dependent Brownian Gyromotion of a Single Skyrmion
|
Non-interacting particles exhibiting Brownian motion have been observed in
many occasions of sciences, such as molecules suspended in liquids, optically
trapped microbeads, and spin textures in magnetic materials. In particular, a
detailed examination of Brownian motion of spin textures is important for
designing thermally stable spintronic devices which motivates the present
study. In this Letter, through using temporally and spatially resolved polar
magneto-optic Kerr effect (MOKE) microscopy, we have experimentally observed
the thermal fluctuation-induced random walk of a single isolated N\'eel-type
magnetic skyrmion in an interfacially asymmetric Ta/CoFeB/TaOx multilayer. An
intriguing topology dependent Brownian gyromotion behavior of skyrmions has
been identified. The onset of Brownian gyromotion of a single skyrmion induced
by the thermal effects, including a nonlinear temperature-dependent diffusion
coefficient and topology-dependent gyromotion are further formulated based on
the stochastic Thiele equation. The experimental and numerical demonstration of
topology-dependent Brownian gyromotion of skyrmions can be useful for
understanding the nonequilibrium magnetization dynamics and implementing
spintronic devices.
|
1901.08206v2
|
2018-02-02
|
Spin wave emission by spin-orbit torque antennas
|
We study the generation of propagating spin waves in Ta/CoFeB waveguides by
spin-orbit torque antennas and compare them to conventional inductive antennas.
The spin-orbit torque was generated by a transverse microwave current across
the magnetic waveguide. The detected spin wave signals for an in-plane
magnetization across the waveguide (Damon-Eshbach configuration) exhibited the
expected phase rotation and amplitude decay upon propagation when the current
spreading was taken into account. Wavevectors up to about 6 rad/$\mu$m could be
excited by the spin-orbit torque antennas despite the current spreading,
presumably due to the non-uniformity of the microwave current. The relative
magnitude of generated anti-damping spin-Hall and Oersted fields was calculated
within an analytic model and it was found that they contribute approximately
equally to the total effective field generated by the spin-orbit torque
antenna. Due to the ellipticity of the precession in the ultrathin waveguide
and the different orientation of the anti-damping spin-Hall and Oersted fields,
the torque was however still dominated by the Oersted field. The prospects for
obtaining a pure spin-orbit torque response are discussed, as are the energy
efficiency and the scaling properties of spin-orbit torque antennas.
|
1802.00861v2
|
2019-02-10
|
Evidence of Pure Spin-Current Generated by Spin Pumping in Interface Localized States in Hybrid Metal-Silicon-Metal Vertical Structures
|
Due to the difficulty to grow high quality semiconductors on ferromagnetic
metals, the study of spin diffusion transport in Si was only limited to lateral
geometry devices. In this work, by using ultra-high vacuum wafer-bonding
technique, we have successfully fabricated metal semiconductor metal
CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current
injection and transport in the perpendicular current flow geometry over a
distance larger than 2\mu m in n-type Si at room temperature. In those
experiments, a pure propagating spin-current is generated via ferromagnetic
resonance spin-pumping and converted into a measurable voltage by using the
inverse spin-Hall effect occurring in the top Pt layer. A systematic study by
varying both Si and MgO thicknesses reveals the important role played by the
localized states at the MgO/Si interface for the spin-current generation.
Proximity effects involving indirect exchange interactions between the
ferromagnet and the MgO/Si interface states appears to be a prerequisite to
establish the necessary out-of-equilibrium spin-population in Si under the
spin-pumping action.
|
1902.03652v1
|
2019-02-19
|
Generation and Hall effect of skyrmions enabled via using nonmagnetic point contacts
|
To enable functional skyrmion based spintronic devices, the controllable
generation and manipulation of skyrmions is essential. While the generation of
skyrmions by using a magnetic geometrical constriction has already been
demonstrated, this approach is difficult to combine with a subsequent
controlled manipulation of skyrmions. The high efficiency of skyrmion
generation from magnetic constrictions limits the useful current density,
resulting in stochastic skyrmion motion, which may obscure topological
phenomena such as the skyrmion Hall effect. In order to address this issue, we
designed a nonmagnetic conducting Ti/Au point contact in devices made of
Ta/CoFeB/TaOx trilayer films. By applying high voltage pulses, we
experimentally demonstrated that skyrmions can be dynamically generated.
Moreover, the accompanied spin topology dependent skyrmion dynamics, the
skyrmion Hall effect is also experimentally observed in the same devices. The
creation process has been numerically reproduced through micromagnetic
simulations in which the important role of skyrmion-antiskyrmion pair
generation is identified. The motion and Hall effect of the skyrmions,
immediately after their creation is described using a modified Thiele equation
after taking into account the contribution from spatially inhomogeneous
spin-orbit torques and the Magnus force. The simultaneous generation and
manipulation of skyrmions using a nonmagnetic point contact could provide a
useful pathway for designing novel skyrmion based devices.
|
1902.06954v1
|
2020-04-05
|
Spin wave based tunable switch between superconducting flux qubits
|
Quantum computing hardware has received world-wide attention and made
considerable progress recently. YIG thin film have spin wave (magnon) modes
with low dissipation and reliable control for quantum information processing.
However, the coherent coupling between a quantum device and YIG thin film has
yet been demonstrated. Here, we propose a scheme to achieve strong coupling
between superconducting flux qubits and magnon modes in YIG thin film. Unlike
the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode or
other spin ensembles, with N the total number of spins, an additional spatial
dependent phase factor needs to be considered when the qubits are magnetically
coupled with the magnon modes of finite wavelength. To avoid undesirable
cancelation of coupling caused by the symmetrical boundary condition, a CoFeB
thin layer is added to one side of the YIG thin film to break the symmetry. Our
numerical simulation demonstrates avoided crossing and coherent transfer of
quantum information between the flux qubits and the standing spin waves in YIG
thin films. We show that the YIG thin film can be used as a tunable switch
between two flux qubits, which have modified shape with small direct inductive
coupling between them. Our results manifest that it is possible to couple flux
qubits while suppressing undesirable cross-talk.
|
2004.02156v1
|
2020-08-14
|
Spin-injection and spin-relaxation in p-doped InGaAs/GaAs quantum-dot spin light emitting diode at zero magnetic field
|
We report on efficient spin injection in p-doped InGaAs/GaAs quantum-dot (QD)
spin light emitting diode (spin-LED) under zero applied magnetic field. A high
degree of electroluminescence circular polarization (Pc) ~19% is measured in
remanence up to 100K. This result is obtained thanks to the combination of a
perpendicularly magnetized CoFeB/MgO spin injector allowing efficient spin
injection and an appropriate p-doped InGaAs/GaAs QD layer in the active region.
By analyzing the bias and temperature dependence of the electroluminescence
circular polarization, we have evidenced a two-step spin relaxation process.
The first step occurs when electrons tunnel through the MgO barrier and travel
across the GaAs depletion layer. The spin relaxation is dominated by the
Dyakonov-Perel mechanism related to the kinetic energy of electrons, which is
characterized by a bias dependent Pc. The second step occurs when electrons are
captured into QDs prior to their radiative recombination with holes. The
temperature dependence of Pc reflects the temperature induced modification of
the QDs doping, together with the variation of the ratio between the charge
carrier lifetime and the spin relaxation time inside the QDs. The understanding
of these spin relaxation mechanisms is essential to improve the performance of
spin LED for future spin optoelectronic applications at room temperature under
zero applied magnetic field.
|
2008.06407v1
|
2020-08-17
|
Enhancement of spin Hall conductivity in W-Ta alloy
|
Generating pure spin currents via the spin Hall effect in heavy metals has
been an active topic of research in the last decade. In order to reduce the
energy required to efficiently switch neighbouring ferromagnetic layers for
applications, one should not only increase the charge- to-spin conversion
efficiency but also decrease the longitudinal resistivity of the heavy metal.
In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} /
CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance
measurements. Alloying W with Ta leads to a factor of two change in both the
damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal
resistivity (60 - 120 {\mu}W cm). At 11% Ta concentration, a remarkably high
spin Hall angle value of - 0.3 is achieved with a low longitudinal resistivity
100 {\mu}W cm, which could lead to a very low power consumption for this
W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a
promising material for power-efficient spin current generation.
|
2008.07572v1
|
2016-02-08
|
External-Field-Free Spin Hall Switching of Perpendicular Magnetic Nanopillar with a Dipole-Coupled Composite Structure
|
Spin Hall effect (SHE) induced reversal of perpendicular magnetization has
attracted significant interest, due to its potential to lead to low power
memory and logic devices. However, the switching requires an assisted in-plane
magnetic field, which hampers its practical applications. Here, we introduce a
novel approach for external-field-free spin Hall switching of a perpendicular
nanomagnet by utilizing a local dipolar field arising from an adjacent in-plane
magnetic layer. Robust switching of perpendicular CoFeB nanopillars in a
dipole-coupled composite stack is experimentally demonstrated in the absence of
any external magnetic field, in consistent with the results of micromagnetic
simulation. Large in-plane compensation field of about 135 Oe and out-of-plane
loop shift of about 45 Oe / 10 7 A cm-2 are obtained in the nanopillar devices
with composite structure. By performing micromagnetic simulations, we confirm
the composite external-field-free switching strategy can also work for a 10 x
10 nm2 circular pillar. Compared with other proposed methods for
external-field-free spin Hall switching of perpendicular magnetization, the
dipole-coupled composite structure is compatible with a wide range of spin Hall
systems and perpendicular magnetic tunnel junctions, paving the way towards
practical SHE-based MRAM and logic applications.
|
1603.09624v2
|
2017-02-16
|
Pumping laser excited spins through MgO barriers
|
We present a study of the tunnel magneto-Seebeck (TMS) effect in MgO based
magnetic tunnel junctions (MTJs). The electrodes consist of CoFeB with in-plane
magnetic anisotropy. The temperature gradients which generate a voltage across
the MTJs layer stack are created using laser heating. Using this method, the
temperature can be controlled on the micrometer length scale: here, we
investigate, how both, the TMS voltage and the TMS effect, depend on the size,
position and intensity of the applied laser spot. For this study, a large
variety of different temperature distributions was created across the junction.
We recorded two-dimensional maps of voltages generated by heating in dependence
of the laser spot position and the corresponding calculated TMS values. The
voltages change in value and sign, from large positive values when heating the
MTJ directly in the centre to small values when heating the junction on the
edges and even small negative values when heating the sample away from the
junction. Those zero crossings lead to very high calculated TMS ratios. Our
systematic analysis shows, that the distribution of the temperature gradient is
essential, to achieve high voltage signals and reasonable resulting TMS ratios.
Furthermore, artefacts on the edges produce misleading results, but also open
up further possibilities of more complex heating scenarios for
spincaloritronics in spintronic devices.
|
1702.05038v1
|
2017-02-21
|
All-optical Detection of Spin Hall Angle in W/CoFeB/SiO2 Heterostructures by Varying Tungsten Layer Thickness
|
The development of advanced spintronics devices hinges on the efficient
generation and utilization of pure spin current. In materials with large
spin-orbit coupling, the spin Hall effect may convert charge current to pure
spin current and a large conversion efficiency, which is quantified by spin
Hall angle (SHA), is desirable for the realization of miniaturized and energy
efficient spintronic devices. Here, we report a giant SHA in beta-tungsten
(\b{eta}-W) thin films in Sub/W(t)/Co20Fe60B20(3 nm)/SiO2(2 nm)
heterostructures with variable W thickness. We employed an all-optical
time-resolved magneto-optical Kerr effect microscope for an unambiguous
determination of SHA using the principle of modulation of Gilbert damping of
the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A
non-monotonic variation of SHA with W layer thickness (t) is observed with a
maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a
very low value at t = 6 nm. This variation of SHA with W-thickness correlates
well with the thickness dependent structural phase transition and resistivity
variation of W above the spin diffusion length of W, while below this length
the interfacial electronic effect at W/CoFeB influences the estimation of SHA.
|
1702.06258v1
|
2019-05-27
|
Unidirectional planar Hall voltages induced by surface acoustic waves in ferromagnetic thin films
|
The electromotive forces induced by surface acoustic waves (SAWs) are
investigated in ferromagnetic thin films. CoFeB thin films deposited on
LiNbO$_3$ substrates are patterned into Hall-bars to study the acoustoelectric
transport properties of the device. The longitudinal and transverse dc voltages
that develop in the Hall bars, which are parallel and orthogonal to the flow of
the SAW, respectively, are measured under application of an in-plane magnetic
field. The longitudinal voltage scales linearly with the SAW power and reverses
its polarity upon changing the direction to which the SAW propagates,
suggesting generation of a dc acoustic current via the SAW excitation. The
magnetic field has little influence on the acoustic current. In contrast, the
SAW induced transverse voltage shows significant dependence on the relative
angle between the magnetic field and the SAW propagation direction. Such field
angle dependent voltage resembles that of the planar Hall voltage induced by
electric current. Interestingly, the angle dependent acoustic transverse
voltage does not depend on the SAW propagation direction. Moreover, the
magnitude of the equivalent angle dependent acoustic transverse resistance is
more than one order of magnitude larger than that of the planar Hall
resistance. These results show the unique acoustoelectric transport properties
of ferromagnetic thin films.
|
1905.11224v1
|
2020-07-23
|
Electrical Detection of Light Helicity using a Quantum Dots based Hybrid Device at Zero Magnetic Field
|
Photon helicity-dependent photocurrent is measured at zero magnetic field on
a device based on an ensemble of InGaAs/GaAs quantum dots that are embedded
into a GaAs-based p-i-n diode. Our main goal is to take advantage of the long
electron spin relaxation time expected in these nano-objects. In these
experiments, no external magnetic field is required thanks to the use of an
ultrathin magnetic CoFeB/MgO electrode, presenting perpendicular magnetic
anisotropy (PMA). We observe a clear asymmetry of the photocurrent measured
under respective right and left polarized light that follows the hysteresis of
the magnetic layer. The amplitude of this asymmetry at zero magnetic field
decreases with increasing temperatures and can be controlled with the bias.
Polarization-resolved photoluminescence is detected in parallel while the
device is operated as a photodetector. This demonstrates the multifunctional
capabilities of the device and gives valuable insights into the spin relaxation
of the electrons in the quantum dots.
|
2007.12054v1
|
2020-12-02
|
Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements
|
Media with engineered magnetization are essential building blocks in
superconductivity, magnetism and magnon spintronics. However, the established
thin-film and lithographic techniques insufficiently suit the realization of
planar components with on-demand-tailored magnetization in the lateral
dimension. Here, we demonstrate the engineering of the magnetic properties of
CoFe-based nanodisks fabricated by the mask-less technique of focused electron
beam induced deposition (FEBID). The material composition in the nanodisks is
tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their
post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange
stiffness $A$ of the disks are deduced from perpendicular ferromagnetic
resonance measurements. The achieved $M_s$ variation in the broad range from
$720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the
$M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The
presented approach paves a way towards nanoscale 2D and 3D systems with
controllable and space-varied magnetic properties.
|
2012.01481v1
|
2021-04-05
|
Analyser-free, intensity-based wide-field magneto-optical microscopy
|
In conventional Kerr- and Faraday microscopy the sample is illuminated with
plane-polarised light and a magnetic domain contrast is generated by an
analyser making use of the Kerr- or Faraday rotation. In this paper we
demonstrate possibilities of analyser-free magneto-optical microscopy based on
magnetisation-dependent intensity modulations of the light: (i) The transverse
Kerr effect can be applied for in-plane magnetised material, demonstrated for
an FeSi sheet. (ii) Illuminating the same sample with circularly polarised
light leads to a domain contrast with a different symmetry as the conventional
Kerr contrast. (iii) Circular polarisation can also be used for perpendicularly
magnetised material, demonstrated for a garnet film and an ultrathin CoFeB
film. (iv) Plane-polarised light at a specific angle can be employed for both,
in-plane and perpendicular media. (v) Perpendicular light incidence leads to a
domain contrast on in-plane materials that is quadratic in the magnetisation
and to a domain boundary contrast. (vi) Domain contrast can even be obtained
without polariser. In cases (ii) and (iii), the contrast is generated by MCD
(Magnetic Circular Dichroism), while MLD (Magnetic Linear Dichroism) is
responsible for the contrast in case (v). The domain boundary contrast is due
to the magneto-optical gradient effect in metallic samples. A domain boundary
contrast can also arise due to interference of phase-shifted magneto-optical
amplitudes. An explanation of these contrast phenomena is provided in terms of
Maxwell-Fresnel theory.
|
2104.01831v2
|
2021-06-29
|
Spin Hall effect in a spin-1 chiral semimetal
|
Spin-1 chiral semimetal is a new state of quantum matter hosting
unconventional chiral fermions that extend beyond the common Dirac and Weyl
fermions. B20-type CoSi is a prototypal material that accommodates such an
exotic quasiparticle. To date, the spin transport properties in the spin-1
chiral semimetals, have not been explored yet. In this work, we fabricated
B20-CoSi thin films on sapphire c-plane substrates by magnetron sputtering and
studied the spin Hall effect (SHE) by combining experiments and
first-principles calculations. The SHE of CoSi using CoSi/CoFeB/MgO
heterostructures was investigated via spin Hall magnetoresistance and harmonic
Hall measurements. First-principles calculations yield an intrinsic spin Hall
conductivity (SHC) at the Fermi level that is consistent with the experiments
and reveal its unique Fermi-energy dependence. Unlike the Dirac and Weyl
fermion-mediated Hall conductivities that exhibit a peak-like structure
centering around the topological node, SHC of B20-CoSi is odd and crosses zero
at the node with two antisymmetric local extrema of opposite sign situated
below and above in energy. Hybridization between Co d-Si p orbitals and
spin-orbit coupling are essential for the SHC, despite the small (~1%) weight
of Si p-orbital near the Fermi level. This work expands the horizon of
topological spintronics and highlights the importance of Fermi-level tuning in
order to fully exploit the topology of spin-1 chiral fermions for spin current
generation.
|
2106.15107v1
|
2021-11-13
|
360° polarization control of terahertz spintronic emitters using uniaxial FeCo/TbCo2/FeCo trilayers
|
Polarization control of THz light is of paramount interest for the numerous
applications offered in this frequency range. Recent developments in THz
spintronic emitters allow for a very efficient broadband emission, and
especially unique is their ability of THz polarization switching through
magnetization control of the ferromagnetic layer. Here we present an improved
scheme to achieve full 360{\deg} nearly coherent polarization rotation that
does not require multipolar or rotating external magnetic bias nor complex
cascaded emitters. By replacing the FM layer of the spintronic emitter with a
carefully designed FeCo/TbCo2/FeCo anisotropic heterostructure, we
experimentally demonstrate Stoner-Wohlfarth-like coherent rotation of the THz
polarization over a full 2pi azimuth only by a bipolar variation of the
strength of the hard axis field, and with only a negligible decrease in the
emission efficiency as compared to standard Pt/CoFeB/W inverse spin Hall
emitters. THz measurements are in agreement with our model of the non-perfect
Stoner-Wohlfarth behaviour. These emitters are well adapted for the
implementation of polarimetric characterization not requiring any mechanically
rotating polarizing elements. An example is given with the characterization of
the birefringence in a quartz plate.
|
2111.07118v1
|
2022-06-07
|
Non-volatile electric control of spin-orbit torques in an oxide two-dimensional electron gas
|
Spin-orbit torques (SOTs) have opened a novel way to manipulate the
magnetization using in-plane current, with a great potential for the
development of fast and low power information technologies. It has been
recently shown that two-dimensional electron gases (2DEGs) appearing at oxide
interfaces provide a highly efficient spin-to-charge current interconversion.
The ability to manipulate 2DEGs using gate voltages could offer a degree of
freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for
spin-orbitronics, in which the sign and amplitude of SOTs at a given current
are fixed by the stack structure. Here, we report the non-volatile
electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We
demonstrate that the 2DEG is controlled using a back-gate electric-field,
providing two remanent and switchable states, with a large resistance contrast
of 1064%. The SOTs can then be controlled electrically in a non-volatile way,
both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO
heterostructures with large perpendicular magnetization further validates the
compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving
the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT
oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.
|
2206.03068v1
|
2022-08-09
|
Growth-dependent Interlayer Chiral Exchange and Field-free Switching
|
Interfacial Dzyaloshinskii-Moriya interaction (DMI) has long been observed in
normal metal/ferromagnetic multilayers, enabling the formation of chiral domain
walls, skyrmions and other 2D antisymmetric spin textures confined within a
single ferromagnetic layer, while more recent works on interlayer DMI reveal
new pathways in realizing novel chiral 3D spin textures between two separate
layers.Here, we report on interlayer DMI between two orthogonally magnetized
ferromagnetic layers (CoFeB/Co) mediated by a Pt layer, and confirm the chiral
nature of the observed effective field of up to 37 Oe through asymmetric
hysteresis loops under in-plane field.We highlight the importance of
growth-induced in-plane symmetry breaking, resulting in a sizable interlayer
DMI and a universal characteristic vector through wedge deposition of the
samples.We further perform deterministic current-driven magnetization switching
in the perpendicularly magnetized Co layer utilizing solely the effective field
from the interlayer DMI.These results demonstrate the potential of interlayer
DMI in facilitating deterministic field-free switching in spin memory
applications.
|
2208.04492v1
|
2022-10-12
|
Depth-dependent magnetic crossover in a room-temperature skyrmion-hosting multilayer
|
Skyrmion-hosting multilayer stacks are promising avenues for applications,
although little is known about the depth dependence of the magnetism. We
address this by reporting the results of circular dichroic resonant elastic
x-ray scattering (CD-REXS), micromagnetic simulations, and low-energy muon-spin
rotation (LE-$\mu^+$SR) measurements on a stack comprising
[Ta/CoFeB/MgO]$_{16}$/Ta on a Si substrate. Energy-dependent CD-REXS shows a
continuous, monotonic evolution of the domain-wall helicity angle with incident
energy, consistent with a three-dimensional hybrid domain-wall-like structure
that changes from N\'eel-like near the surface to Bloch-like deeper within the
sample. LE-$\mu^+$SR reveals that the magnetic field distribution in the
trilayers near the surface of the stack is distinct from that in trilayers
deeper within the sample. Our micromagnetic simulations support a quantitative
analysis of the $\mu^+$SR results. By increasing the applied magnetic field, we
find a reduction in the volume occupied by domain walls at all depths,
consistent with a crossover into a region dominated by skyrmions above
approximately 180 mT.
|
2210.06070v2
|
2022-12-15
|
Emulation of Neuron and Synaptic Functions in Spin-Orbit Torque Domain Wall Devices
|
Neuromorphic computing (NC) architecture has shown its suitability for
energy-efficient computation. Amongst several systems, spin-orbit torque (SOT)
based domain wall (DW) devices are one of the most energy-efficient contenders
for NC. To realize spin-based NC architecture, the computing elements such as
synthetic neurons and synapses need to be developed. However, there are very
few experimental investigations on DW neurons and synapses. The present study
demonstrates the energy-efficient operations of neurons and synapses by using
novel reading and writing strategies. We have used a W/CoFeB-based
energy-efficient SOT mechanism to drive the DWs at low current densities. We
have used the concept of meander devices for achieving synaptic functions. By
doing this, we have achieved 9 different resistive states in experiments. We
have experimentally demonstrated the functional spike and step neurons.
Additionally, we have engineered the anomalous Hall bars by incorporating
several pairs, in comparison to conventional Hall crosses, to increase the
sensitivity as well as signal-to-noise ratio (SNR). We performed micromagnetic
simulations and transport measurements to demonstrate the above-mentioned
functionalities.
|
2212.07833v1
|
2023-01-10
|
Robust mutual synchronization in long spin Hall nano-oscillator chains
|
Mutual synchronization of N serially connected spintronic nano-oscillators
increases their coherence by a factor $N$ and their output power by $N^2$.
Increasing the number of mutually synchronized nano-oscillators in chains is
hence of great importance for better signal quality and also for emerging
applications such as oscillator-based neuromorphic computing and Ising machines
where larger N can tackle larger problems. Here we fabricate spin Hall
nano-oscillator chains of up to 50 serially connected nano-constrictions in
W/NiFe, W/CoFeB/MgO, and NiFe/Pt stacks and demonstrate robust and complete
mutual synchronization of up to 21 nano-constrictions, reaching linewidths of
below 200 kHz and quality factors beyond 79,000, while operating at 10 GHz. We
also find a square increase in the peak power with the increasing number of
mutually synchronized oscillators, resulting in a factor of 400 higher peak
power in long chains compared to individual nano-constrictions. Although chains
longer than 21 nano-constrictions also show complete mutual synchronization, it
is not as robust and their signal quality does not improve as much as they
prefer to break up into partially synchronized states. The low current and low
field operation of these oscillators along with their wide frequency tunability
(2-28 GHz) with both current and magnetic fields, make them ideal candidates
for on-chip GHz-range applications and neuromorphic computing.
|
2301.03859v1
|
2023-02-02
|
Controlling the Skyrmion Density and Size for Quantized Convolutional Neural Networks
|
Skyrmion devices show energy efficient and high integration data storage and
computing capabilities. Herein, we present the results of experimental and
micromagnetic investigations of the creation and stability of magnetic
skyrmions in the Ta/IrMn/CoFeB/MgO thin film system. We investigate the
magnetic-field dependence of the skyrmion density and size using polar magneto
optical Kerr effect MOKE microscopy supported by a micromagnetic study. The
evolution of the topological charge with time under a magnetic field is
investigated, and the transformation dynamics are explained. Furthermore,
considering the voltage control of these skyrmion devices, we evaluate the
dependence of the skyrmion size and density on the Dzyaloshinskii Moriya
interaction and the magnetic anisotropy. We furthermore propose a skyrmion
based synaptic device based on the results of the MOKE and micromagnetic
investigations. We demonstrate the spin-orbit torque controlled discrete
topological resistance states with high linearity and uniformity in the device.
The discrete nature of the topological resistance makes it a good candidate to
realize hardware implementation of weight quantization in a quantized neural
network (QNN). The neural network is trained and tested on the CIFAR10 dataset,
where the devices act as synapses to achieve a recognition accuracy of 87%,
which is comparable to the result of ideal software-based methods.
|
2302.01390v1
|
2023-04-16
|
Anomalous and Topological Hall Resistivity in Ta/CoFeB/MgO Magnetic Systems for Neuromorphic Computing Applications
|
Topologically protected spin textures, such as magnetic skyrmions, have the
potential for dense data storage as well as energy-efficient computing due to
their small size and a low driving current. The evaluation of the writing and
reading of the skyrmion's magnetic and electrical characteristics is a key step
toward the implementation of these devices. In this paper, we present the
magnetic heterostructure Hall bar device and study the anomalous Hall and
topological Hall signals in the device. Using the combination of different
measurements like magnetometry at different temperatures, Hall effect
measurement from 2K to 300K, and magnetic force microscopy imaging, we
investigate the magnetic and electrical characteristics of the magnetic
structure. We measure the skyrmion topological resistivity at different
temperatures as a function of the magnetic field. The topological resistivity
is maximum around the zero magnetic field and it decreases to zero at the
saturating field. This is further supported by MFM imaging. Interestingly the
resistivity decreases linearly with the field, matching the behavior observed
in the corresponding micromagnetic simulations. We combine the experimental
results with micromagnetic simulations, thus propose a skyrmion-based synaptic
device and show spin-orbit torque-controlled potentiation/depression in the
device. The device performance as the synapse for neuromorphic computing is
further evaluated in a convolutional neural network CNN. The neural network is
trained and tested on the MNIST data set we show devices acting as synapses
achieving a recognition accuracy close to 90%, on par with the ideal
software-based weights which offer an accuracy of 92%.
|
2304.07742v1
|
2023-06-28
|
Suppression of the spin waves nonreciprocity due to interfacial Dzyaloshinskii Moriya interaction by lateral confinement in magnetic nanostructures
|
Despite the huge recent interest towards chiral magnetism related to the
interfacial Dzyaloshinskii Moriya interaction (iDMI) in layered systems, there
is a lack of experimental data on the effect of iDMI on the spin waves
eigenmodes of laterally confined nanostructures. Here we exploit Brillouin
Light Scattering (BLS) to analyze the spin wave eigenmodes of non-interacting
circular and elliptical dots, as well as of long stripes, patterned starting
from a Pt(3.4 nm)/CoFeB(0.8 nm) bilayer, with lateral dimensions ranging from
100 nm to 400 nm. Our experimental results, corroborated by micromagnetic
simulations based on the GPU-accelerated MuMax3 software package, provide
evidence for a strong suppression of the frequency asymmetry between
counter-propagating spin waves (corresponding to either Stokes or anti-Stokes
peaks in BLS spectra), when the lateral confinement is reduced from 400 nm to
100 nm, i.e. when it becomes lower than the light wavelength. Such an evolution
reflects the modification of the spin wave character from propagating to
stationary and indicates that the BLS based method of quantifying the i-DMI
strength from the frequency difference of counter propagating spin waves is not
applicable in the case of magnetic elements with lateral dimension below about
400 nm.
|
2306.16310v1
|
2023-09-27
|
Impact of surface anisotropy on the spin-wave dynamics in thin ferromagnetic film
|
The spin-wave dynamics in the thin CoFeB film in Damon-Eshbach geometry are
studied in three cases of boundary conditions -- free boundary conditions,
symmetrical surface anisotropy, and one-sided surface anisotropy. The
analytical model created by Wolfram and De Wames was extended to include
perpendicular surface anisotropy in boundary conditions. Its comparison with
numerical simulations demonstrate perfect agreement between the approaches. The
analysis of the dispersion relation indicates that the presence of surface
anisotropy increases the avoided crossing size between Damon-Eshbach mode and
perpendicular standing modes. Additionally, asymmetrical one-sided surface
anisotropy induces nonreciprocity in the dispersion relation. In-depth analysis
of the avoided crossing size is conducted for systems with different boundary
conditions, different thicknesses, surface anisotropy constant values, and
external magnetic fields. It shows the significant role of the strength of
surface localization of Damon-Eshbach mode and the symmetry of perpendicular
standing modes in the avoided crossing broadening. Interestingly, for specific
set of parameters the interaction between the particular modes can be
suppressed, resulting in a mode crossing. Such a crossing, which occurs only on
one side of the dispersion relation in a one-sided surface anisotropy system,
can be utilized in nonreciprocal devices.
|
2309.15583v1
|
2023-11-15
|
Low voltage local strain enhanced switching of magnetic tunnel junctions
|
Strain-controlled modulation of the magnetic switching behavior in magnetic
tunnel junctions (MTJs) could provide the energy efficiency needed to
accelerate the use of MTJs in memory, logic, and neuromorphic computing, as
well as an additional way to tune MTJ properties for these applications.
State-of-the-art CoFeB-MgO based MTJs still require too high voltages to alter
their magnetic switching behavior with strain. In this study, we demonstrate
strain-enhanced field switching of nanoscale MTJs through electric field
control via voltage applied across local gates. The results show that
record-low voltage down to 200 mV can be used to control the switching field of
the MTJ through enhancing the magnetic anisotropy, and that tunnel
magnetoresistance is linearly enhanced with voltage through straining the
crystal structure of the tunnel barrier. These findings underscore the
potential of electric field manipulation and strain engineering as effective
strategies for tailoring the properties and functionality of nanoscale MTJs.
|
2311.08984v2
|
2023-11-24
|
Even-in-magnetic-field part of transverse resistivity as a probe of magnetic order
|
The detection of a voltage transverse to both an applied current and a
magnetic field is one of the most common characterization techniques in
solid-state physics. The corresponding component of the resistivity tensor
$\rho_{ij}$ can be separated into odd and even parts with respect to the
applied magnetic field. The former contains information, for example, about the
ordinary or anomalous Hall effect. The latter is typically ascribed to
experimental artefacts and ignored. We here show that upon suppressing these
artefacts in carefully controlled experiments, useful information remains. We
first investigate the well-explored ferromagnet CoFeB, where the even part of
$\rho_{yx}$ contains a contribution from the anisotropic magnetoresistance,
which we confirm by Stoner-Wohlfarth modelling. We then apply our approach to
magnetotransport measurements in $\rm Mn_5Si_3$ thin films with a complex
compensated magnetic order. In this material, the even part of the transverse
signal is sizable only in the low-spin-symmetry phase below $\approx 80$ K and
thus offers a simple and readily available probe of the magnetic order.
|
2311.14498v1
|
2024-03-25
|
Skyrmionic device for three dimensional magnetic field sensing enabled by spin-orbit torques
|
Magnetic skyrmions are topologically protected local magnetic solitons that
are promising for storage, logic or general computing applications. In this
work, we demonstrate that we can use a skyrmion device based on [W/CoFeB/MgO] 1
0 multilayers for three-dimensional magnetic field sensing enabled by
spin-orbit torques (SOT). We stabilize isolated chiral skyrmions and stripe
domains in the multilayers, as shown by magnetic force microscopy images and
micromagnetic simulations. We perform magnetic transport measurements to show
that we can sense both in-plane and out-of-plane magnetic fields by means of a
differential measurement scheme in which the symmetry of the SOT leads to
cancelation of the DC offset. With the magnetic parameters obtained by
vibrating sample magnetometry and ferromagnetic resonance measurements, we
perform finite-temperature micromagnetic simulations, where we investigate the
fundamental origin of the sensing signal. We identify the topological
transformation between skyrmions, stripes and type-II bubbles that leads to a
change in the resistance that is read-out by the anomalous Hall effect. Our
study presents a novel application for skyrmions, where a differential
measurement sensing concept is applied to quantify external magnetic fields
paving the way towards more energy efficient applications in skyrmionics based
spintronics.
|
2403.16725v1
|
2020-09-14
|
Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect
|
We investigated temperature dependent current driven spin-orbit torques in
magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures
with in-plane magnetic anisotropy. The room temperature damping-like and
field-like spin torque efficiencies of the amorphous Ru2Sn3 films were measured
to be 0.14 +- 0.008 (0.07 +- 0.012) and -0.03 +- 0.006 (-0.20 +- 0.009), for
the 4 (10 nm) films respectively, by utilizing the second harmonic Hall
technique. The large field-like torque in the relatively thicker Ru2Sn3 (10 nm)
thin film is unique compared to the traditional spin Hall materials interfaced
with thick magnetic layers with in-plane magnetic anisotropy which typically
have dominant damping-like and negligible field-like torques. Additionally, the
observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB
(5 nm) is up to three times larger than the damping-like torque (-0.20 +- 0.009
and 0.07 +- 0.012, respectively) and thirty times larger at 50 K (-0.29 +-
0.014 and 0.009 +- 0.017, respectively). The temperature dependence of the
field-like torques show dominant contributions from the intrinsic spin Hall
effect while the damping-like torques show dominate contributions from the
extrinsic spin Hall effects, skew scattering and side jump. Through macro-spin
calculations, we found that including field-like torques on the order or larger
than the damping-like torque can reduce the switching critical current and
decrease magnetization procession for a perpendicular ferromagnetic layer.
|
2009.06711v2
|
2021-11-09
|
Spintronic emitters for super-resolution in THz-spectral imaging
|
THz-spectroscopy is an attractive imaging tool for scientific research,
especially in life science, offering non-destructive interaction with matter
due to its low photon energies. However, wavelengths above $100{\mu}m$
principally limit its spatial resolution in the far-field by diffraction to
this regime, making it not sufficient to image biological cells in the
micrometer scale. Therefore, super-resolution imaging techniques are required
to overcome this restriction. Near-field-imaging using spintronic emitters
offers the most feasible approach because of its simplicity and potential for
wide-ranging applications. In our study, we investigate THz-radiation generated
by fs-laser-pulses in CoFeB/Pt heterostructures, based on spin currents,
detected by commercial LT-GaAs Auston switches. The spatial resolution is
evaluated applying a 2D scanning technique with motorized stages allowing
scanning steps in the sub-micrometer range. By applying near-field imaging we
can increase the spatial resolution to the dimensions of the laser spot size in
the micrometer scale. For this purpose, the spintronic emitter is directly
evaporated on a gold test pattern separated by a 300 nm spacer layer. Moving
these structures with respect to the femtosecond laser spot which generates the
THz radiation allows for resolution determination using the knife-edge method.
We observe a full-width half-maximum THz beam diameter of $4.9(4){\mu}$m at 1
THz. The possibility to deposit spintronic emitter heterostructures on simple
glass substrates makes them an interesting candidate for near-field imaging for
a large number of applications.
|
2111.05023v1
|
2010-03-24
|
Dynamical shift condition for unequal mass black hole binaries
|
Certain numerical frameworks used for the evolution of binary black holes
make use of a gamma driver, which includes a damping factor. Such simulations
typically use a constant value for damping. However, it has been found that
very specific values of the damping factor are needed for the calculation of
unequal mass binaries. We examine carefully the role this damping plays, and
provide two explicit, non-constant forms for the damping to be used with
mass-ratios further from one. Our analysis of the resultant waveforms compares
well against the constant damping case.
|
1003.4681v1
|
2013-05-21
|
Characterization and Synthesis of Rayleigh Damped Elastodynamic Networks
|
We consider damped elastodynamic networks where the damping matrix is assumed
to be a non-negative linear combination of the stiffness and mass matrices
(also known as Rayleigh or proportional damping). We give here a
characterization of the frequency response of such networks. We also answer the
synthesis question for such networks, i.e., how to construct a Rayleigh damped
elastodynamic network with a given frequency response. Our analysis shows that
not all damped elastodynamic networks can be realized when the proportionality
constants between the damping matrix and the mass and stiffness matrices are
fixed.
|
1305.4961v1
|
2009-05-20
|
Eigenvalue asymptotics, inverse problems and a trace formula for the linear damped wave equation
|
We determine the general form of the asymptotics for Dirichlet eigenvalues of
the one-dimensional linear damped wave operator. As a consequence, we obtain
that given a spectrum corresponding to a constant damping term this determines
the damping term in a unique fashion. We also derive a trace formula for this
problem.
|
0905.3242v1
|
2002-06-27
|
Initial-amplitude dependence in weakly damped oscillators
|
A pedagogically instructive experimental procedure is suggested for
distinguishing between different damping terms in a weakly damped oscillator,
which highclights the connection between non-linear damping and
initial-amplitude dependence. The most common damping terms such as contact
friction, air resistance, viscous drag, and electromagnetic damping have
velocity dependences of the form constant, v, or v^2. The corresponding energy
dependences of the form \sqrt{E}, E, or E\sqrt{E} in the energy loss equation
give rise to characteristic dependence of the amplitude decay slope on the
initial amplitude.
|
0206086v1
|
2007-08-24
|
Enhancement of the Gilbert damping constant due to spin pumping in noncollinear ferromagnet/nonmagnet/ferromagnet trilayer systems
|
We analyzed the enhancement of the Gilbert damping constant due to spin
pumping in non-collinear ferromagnet / non-magnet / ferromagnet trilayer
systems. We show that the Gilbert damping constant depends both on the
precession angle of the magnetization of the free layer and on the direction of
the magntization of the fixed layer. We find the condition to be satisfied to
realize strong enhancement of the Gilbert damping constant.
|
0708.3323v1
|
2007-03-12
|
Quantum estimation of a damping constant
|
We discuss an interferometric approach to the estimation of quantum
mechanical damping. We study specific classes of entangled and separable probe
states consisting of superpositions of coherent states. Based on the assumption
of limited quantum resources we show that entanglement improves the estimation
of an unknown damping constant.
|
0703091v2
|
2023-09-20
|
Evaluating Gilbert Damping in Magnetic Insulators from First Principles
|
Magnetic damping has a significant impact on the performance of various
magnetic and spintronic devices, making it a long-standing focus of research.
The strength of magnetic damping is usually quantified by the Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation. Here we propose a
first-principles based approach to evaluate the Gilbert damping constant
contributed by spin-lattice coupling in magnetic insulators. The approach
involves effective Hamiltonian models and spin-lattice dynamics simulations. As
a case study, we applied our method to Y$_3$Fe$_5$O$_{12}$, MnFe$_2$O$_4$ and
Cr$_2$O$_3$. Their damping constants were calculated to be $0.8\times10^{-4}$,
$0.2\times10^{-4}$, $2.2\times 10^{-4}$, respectively at a low temperature. The
results for Y$_3$Fe$_5$O$_{12}$ and Cr$_2$O$_3$ are in good agreement with
experimental measurements, while the discrepancy in MnFe$_2$O$_4$ can be
attributed to the inhomogeneity and small band gap in real samples. The
stronger damping observed in Cr$_2$O$_3$, compared to Y$_3$Fe$_5$O$_{12}$,
essentially results from its stronger spin-lattice coupling. In addition, we
confirmed a proportional relationship between damping constants and the
temperature difference of subsystems, which had been reported in previous
studies. These successful applications suggest that our approach serves as a
promising candidate for estimating the Gilbert damping constant in magnetic
insulators.
|
2309.11152v1
|
2020-11-11
|
Reduction of back switching by large damping ferromagnetic material
|
Recent studies on magnetization dynamics induced by spin-orbit torque have
revealed a weak dependence of the critical current for magnetization switching
on the damping constant of a ferromagnetic free layer. This study, however,
reveals that the damping constant nevertheless plays a key role in
magnetization switching induced by spin-orbit torque. An undesirable switching,
returning to an initial state, named as back switching, occurs in a ferromagnet
with an easy axis parallel to the current direction. Numerical and theoretical
analyses reveal that back switching is strongly suppressed when the damping
constant of the ferromagnet is large.
|
2011.05566v1
|
2007-05-14
|
Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations
|
The Landau-Lifshitz equation reliably describes magnetization dynamics using
a phenomenological treatment of damping. This paper presents first-principles
calculations of the damping parameters for Fe, Co, and Ni that quantitatively
agree with existing ferromagnetic resonance measurements. This agreement
establishes the dominant damping mechanism for these systems and takes a
significant step toward predicting and tailoring the damping constants of new
materials.
|
0705.1990v1
|
2015-11-16
|
Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time resolved precessional magnetization measurements
|
Magnetization dynamics are strongly influenced by damping. An effective
damping constant {\alpha}eff is often determined experimentally from the
spectral linewidth of the free induction decay of the magnetization after the
system is excited to its non-equilibrium state. Such an {\alpha}eff, however,
reflects both intrinsic damping as well as inhomogeneous broadening. In this
paper we compare measurements of the magnetization dynamics in ultrathin
non-epitaxial films having perpendicular magnetic anisotropy using two
different techniques, time-resolved magneto optical Kerr effect (TRMOKE) and
hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external
magnetic field that is applied at very small angles to the film plane in the
TRMOKE studies, we develop an explicit closed-form analytical expression for
the TRMOKE spectral linewidth and show how this can be used to reliably extract
the intrinsic Gilbert damping constant. The damping constant determined in this
way is in excellent agreement with that determined from the OFMR method on the
same samples. Our studies indicate that the asymptotic high-field approach that
is often used in the TRMOKE method to distinguish the intrinsic damping from
the effective damping may result in significant error, because such high
external magnetic fields are required to make this approach valid that they are
out of reach. The error becomes larger the lower is the intrinsic damping
constant, and thus may account for the anomalously high damping constants that
are often reported in TRMOKE studies. In conventional ferromagnetic resonance
(FMR) studies, inhomogeneous contributions can be readily distinguished from
intrinsic damping contributions from the magnetic field dependence of the FMR
linewidth. Using the analogous approach, we show how reliable values of the
intrinsic damping can be extracted from TRMOKE.
|
1511.04802v1
|
2006-06-27
|
Theoretical limit of the minimal magnetization switching field and the optimal field pulse for Stoner particles
|
The theoretical limit of the minimal magnetization switching field and the
optimal field pulse design for uniaxial Stoner particles are investigated. Two
results are obtained. One is the existence of a theoretical limit of the
smallest magnetic field out of all possible designs. It is shown that the limit
is proportional to the damping constant in the weak damping regime and
approaches the Stoner-Wohlfarth (SW) limit at large damping. For a realistic
damping constant, this limit is more than ten times smaller than that of
so-called precessional magnetization reversal under a non-collinear static
field. The other is on the optimal field pulse design: If the magnitude of a
magnetic field does not change, but its direction can vary during a reversal
process, there is an optimal design that gives the shortest switching time. The
switching time depends on the field magnitude, damping constant, and magnetic
anisotropy. However, the optimal pulse shape depends only on the damping
constant.
|
0606681v1
|
2022-02-10
|
Non-stationary Anderson acceleration with optimized damping
|
Anderson acceleration (AA) has a long history of use and a strong recent
interest due to its potential ability to dramatically improve the linear
convergence of the fixed-point iteration. Most authors are simply using and
analyzing the stationary version of Anderson acceleration (sAA) with a constant
damping factor or without damping. Little attention has been paid to
nonstationary algorithms. However, damping can be useful and is sometimes
crucial for simulations in which the underlying fixed-point operator is not
globally contractive. The role of this damping factor has not been fully
understood. In the present work, we consider the non-stationary Anderson
acceleration algorithm with optimized damping (AAoptD) in each iteration to
further speed up linear and nonlinear iterations by applying one extra
inexpensive optimization. We analyze this procedure and develop an efficient
and inexpensive implementation scheme. We also show that, compared with the
stationary Anderson acceleration with fixed window size sAA(m), optimizing the
damping factors is related to dynamically packaging sAA(m) and sAA(1) in each
iteration (alternating window size $m$ is another direction of producing
non-stationary AA). Moreover, we show by extensive numerical experiments that
the proposed non-stationary Anderson acceleration with optimized damping
procedure often converges much faster than stationary AA with constant damping
or without damping.
|
2202.05295v1
|
2012-08-01
|
Artificial Neural Network Based Prediction of Optimal Pseudo-Damping and Meta-Damping in Oscillatory Fractional Order Dynamical Systems
|
This paper investigates typical behaviors like damped oscillations in
fractional order (FO) dynamical systems. Such response occurs due to the
presence of, what is conceived as, pseudo-damping and meta-damping in some
special class of FO systems. Here, approximation of such damped oscillation in
FO systems with the conventional notion of integer order damping and time
constant has been carried out using Genetic Algorithm (GA). Next, a multilayer
feed-forward Artificial Neural Network (ANN) has been trained using the GA
based results to predict the optimal pseudo and meta-damping from knowledge of
the maximum order or number of terms in the FO dynamical system.
|
1208.0318v1
|
2005-03-24
|
Fast magnetization switching of Stoner particles: A nonlinear dynamics picture
|
The magnetization reversal of Stoner particles is investigated from the point
of view of nonlinear dynamics within the Landau-Lifshitz-Gilbert formulation.
The following results are obtained. 1) We clarify that the so-called
Stoner-Wohlfarth (SW) limit becomes exact when damping constant is infinitely
large. Under the limit, the magnetization moves along the steepest energy
descent path. The minimal switching field is the one at which there is only one
stable fixed point in the system. 2) For a given magnetic anisotropy, there is
a critical value for the damping constant, above which the minimal switching
field is the same as that of the SW-limit. 3) We illustrate how fixed points
and their basins change under a field along different directions. This change
explains well why a non-parallel field gives a smaller minimal switching field
and a short switching time. 4) The field of a ballistic magnetization reversal
should be along certain direction window in the presence of energy dissipation.
The width of the window depends on both of the damping constant and the
magnetic anisotropy. The upper and lower bounds of the direction window
increase with the damping constant. The window width oscillates with the
damping constant for a given magnetic anisotropy. It is zero for both zero and
infinite damping. Thus, the perpendicular field configuration widely employed
in the current experiments is not the best one since the damping constant in a
real system is far from zero.
|
0503594v1
|
2021-02-01
|
Global existence for semilinear wave equations with scaling invariant damping in 3-D
|
Global existence for small data Cauchy problem of semilinear wave equations
with scaling invariant damping in 3-D is established in this work, assuming
that the data are radial and the constant in front of the damping belongs to
$[1.5, 2)$. The proof is based on a weighted $L^2-L^2$ estimate for
inhomogeneous wave equation, which is established by interpolating between
energy estimate and Morawetz type estimate.
|
2102.00909v1
|
1997-07-23
|
Riccati parameter modes from Newtonian free damping motion by supersymmetry
|
We determine the class of damped modes \tilde{y} which are related to the
common free damping modes y by supersymmetry. They are obtained by employing
the factorization of Newton's differential equation of motion for the free
damped oscillator by means of the general solution of the corresponding Riccati
equation together with Witten's method of constructing the supersymmetric
partner operator. This procedure leads to one-parameter families of (transient)
modes for each of the three types of free damping, corresponding to a
particular type of %time-dependent angular frequency. %time-dependent,
antirestoring acceleration (adding up to the usual Hooke restoring
acceleration) of the form a(t)=\frac{2\gamma ^2}{(\gamma t+1)^{2}}\tilde{y},
where \gamma is the family parameter that has been chosen as the inverse of the
Riccati integration constant. In supersymmetric terms, they represent all those
one Riccati parameter damping modes having the same Newtonian free damping
partner mode
|
9707019v4
|
2014-01-15
|
Damping of Terahertz Plasmons in Graphene Coupled with Surface Plasmons in Heavily-Doped Substrate
|
Coupling of plasmons in graphene at terahert (THz) frequencies with surface
plasmons in a heavily-doped substrate is studied theoretically. We reveal that
a huge scattering rate may completely damp out the plasmons, so that proper
choices of material and geometrical parameters are essential to suppress the
coupling effect and to obtain the minimum damping rate in graphene. Even with
the doping concentration 10^{19} - 10^{20} cm^{-3} and the thickness of the
dielectric layer between graphene and the substrate 100 nm, which are typical
values in real graphene samples with a heavily-doped substrate, the increase in
the damping rate is not negligible in comparison with the
acoustic-phonon-limited damping rate. Dependence of the damping rate on
wavenumber, thicknesses of graphene-to-substrate and gate-to-graphene
separation, substrate doping concentration, and dielectric constants of
surrounding materials are investigated. It is shown that the damping rate can
be much reduced by the gate screening, which suppresses the field spread of the
graphene plasmons into the substrate.
|
1401.3396v1
|
2018-03-29
|
Giant resonant nonlinear damping in nanoscale ferromagnets
|
Magnetic damping is a key metric for emerging technologies based on magnetic
nanoparticles, such as spin torque memory and high-resolution biomagnetic
imaging. Despite its importance, understanding of magnetic dissipation in
nanoscale ferromagnets remains elusive, and the damping is often treated as a
phenomenological constant. Here we report the discovery of a giant
frequency-dependent nonlinear damping that strongly alters the response of a
nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
damping mechanism originates from three-magnon scattering that is strongly
enhanced by geometric confinement of magnons in the nanomagnet. We show that
the giant nonlinear damping can invert the effect of spin torque on a
nanomagnet leading to a surprising current-induced enhancement of damping by an
antidamping torque. Our work advances understanding of magnetic dynamics in
nanoscale ferromagnets and spin torque devices.
|
1803.10925v1
|
2018-02-15
|
Damping's effect on the magnetodynamics of spin Hall nano-oscillators
|
We study the impact of spin wave damping ($\alpha$) on the auto-oscillation
properties of nano-constriction based spin Hall nano-oscillators (SHNOs). The
SHNOs are based on a 5 nm Pt layer interfaced to a 5 nm
Py$_{100-x-y}$Pt$_{x}$Ag$_{y}$ magnetic layer, where the Pt and Ag contents are
co-varied to keep the saturation magnetization constant (within 10 %), while
$\alpha$ varies close to a factor of three. We systematically investigate the
influence of the Gilbert damping on the magnetodynamics of these SHNOs by means
of electrical microwave measurements. Under the condition of a constant field,
the threshold current scales with the damping in the magnetic layer. The
threshold current as a function of field shows a parabolic-like behavior, which
we attribute to the evolution of the spatial profile of the auto-oscillation
mode. The signal linewidth is smaller for the high-damping materials in low
magnetic fields, although the lowest observed linewidth was measured for the
alloy with least damping.
|
1802.05548v1
|
2003-09-09
|
Traveling solitons in the damped driven nonlinear Schrödinger equation
|
The well known effect of the linear damping on the moving nonlinear
Schr\"odinger soliton (even when there is a supply of energy via the spatially
homogeneous driving) is to quench its momentum to zero. Surprisingly, the zero
momentum does not necessarily mean zero velocity. We show that two or more
parametrically driven damped solitons can form a complex traveling with zero
momentum at a nonzero constant speed.
All traveling complexes we have found so far, turned out to be unstable.
Thus, the parametric driving is capable of sustaining the uniform motion of
damped solitons, but some additional agent is required to stabilize it.
|
0309031v1
|
2007-08-28
|
Linear frictional forces cause orbits to neither circularize nor precess
|
For the undamped Kepler potential the lack of precession has historically
been understood in terms of the Runge-Lenz symmetry. For the damped Kepler
problem this result may be understood in terms of the generalization of Poisson
structure to damped systems suggested recently by Tarasov[1]. In this
generalized algebraic structure the orbit-averaged Runge-Lenz vector remains a
constant in the linearly damped Kepler problem to leading order in the damping
coe
|
0708.3827v3
|
2008-12-11
|
Frequency-dependent Drude damping in Casimir force calculations
|
The Casimir force is calculated between Au thin films that are described by a
Drude model with a frequency dependent damping function. The model parameters
are obtained from available experimental data for Au thin films. Two cases are
considered; annealed and nonannealed films that have a different damping
function. Compared with the calculations using a Drude model with a constant
damping parameter, we observe changes in the Casimir force of a few percent.
This behavior is only observed in films of no more than 300 $\AA$ thick.
|
0812.2209v1
|
2009-11-05
|
Bloch oscillations in lattice potentials with controlled aperiodicity
|
We numerically investigate the damping of Bloch oscillations in a
one-dimensional lattice potential whose translational symmetry is broken in a
systematic manner, either by making the potential bichromatic or by introducing
scatterers at distinct lattice sites. We find that the damping strongly depends
on the ratio of lattice constants in the bichromatic potential, and that even a
small concentration of scatterers can lead to strong damping. Moreover,
mean-field interactions are able to counteract aperiodicity-induced damping of
Bloch oscillations.
|
0911.1108v3
|
2012-05-11
|
On radiative damping in plasma-based accelerators
|
Radiative damping in plasma-based electron accelerators is analyzed. The
electron dynamics under combined influence of the constant accelerating force
and the classical radiation reaction force is studied. It is shown that
electron acceleration cannot be limited by radiation reaction. If initially the
accelerating force was stronger than the radiation reaction force then the
electron acceleration is unlimited. Otherwise the electron is decelerated by
radiative damping up to a certain instant of time and then accelerated without
limits. Regardless of the initial conditions the infinite-time asymptotic
behavior of an electron is governed by self-similar solution providing
unlimited acceleration. The relative energy spread induced by the radiative
damping decreases with time in the infinite-time limit.
|
1205.2436v1
|
2016-05-23
|
Large time behaivor of global solutions to nonlinear wave equations with frictional and viscoelastic damping terms
|
In this paper, we study the Cauchy problem for a nonlinear wave equation with
frictional and viscoelastic damping terms. As is pointed out by [8], in this
combination, the frictional damping term is dominant for the viscoelastic one
for the global dynamics of the linear equation. In this note we observe that if
the initial data is small, the frictional damping term is again dominant even
in the nonlinear equation case. In other words, our main result is diffusion
phenomena: the solution is approximated by the heat kernel with a suitable
constant. Our proof is based on several estimates for the corresponding linear
equations.
|
1605.07232v1
|
2021-02-28
|
Stability for an inverse source problem of the damped biharmonic plate equation
|
This paper is concerned with the stability of the inverse source problem for
the damped biharmonic plate equation in three dimensions. The stability
estimate consists of the Lipschitz type data discrepancy and the high frequency
tail of the source function, where the latter decreases as the upper bound of
the frequency increases. The stability also shows exponential dependence on the
constant damping coefficient. The analysis employs Carleman estimates and time
decay estimates for the damped plate wave equation to obtain an exact
observability bound and depends on the study of the resonance-free region and
an upper bound of the resolvent of the biharmonic operator with respect to the
complex wavenumber.
|
2103.00461v1
|
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