196 research outputs found
Light--absorbed orbital angular momentum in the linear response regime
In exploring the light-induced dynamics within the linear response regime,
this study investigates the induced orbital angular momentum on a wide variety
of electronic structures. We derive a general expression for the torque induced
by light on different electronic systems based on their characteristic
dielectric tensor. We demonstrate that this phenomenon diverges from the
inverse Faraday effect as it produces an orbital magnetization persistent
post-illumination. Indeed, our results reveal that, while isotropic
non-dissipative materials do not absorb orbital angular momentum from
circularly polarized light, any symmetry-breaking arrangement of matter, be it
spatial or temporal, introduces novel channels for the absorption of orbital
angular momentum, or magnetization. Most notably, in dissipative materials,
circularly polarized light imparts a torque corresponding to a change in
orbital angular momentum of per absorbed photon. The potential of these
mechanisms to drive helicity-dependent magnetic phenomena paves the way for a
deeper understanding of light-matter interactions. Notably, the application of
pump-probe techniques in tandem with our findings allows experimentalists to
quantitatively assess the amount of orbital angular momentum transferred to
electrons in matter, thus hopefully enhancing our ability to steer ultrafast
light-induced magnetization dynamics
Bimodal switching field distributions in all-perpendicular spin-valve nanopillars
Switching field measurements of the free layer element of 75 nm diameter
spin-valve nanopillars reveal a bimodal distribution of switching fields at low
temperatures (below 100 K). This result is inconsistent with a model of thermal
activation over a single perpendicular anisotropy barrier. The correlation
between antiparallel to parallel and parallel to antiparallel switching fields
increases to nearly 50% at low temperatures. This reflects random fluctuation
of the shift of the free layer hysteresis loop between two different
magnitudes, which may originate from changes in the dipole field from the
polarizing layer. The magnitude of the loop shift changes by 25% and is
correlated to transitions of the spin-valve into an antiparallel configuration.Comment: 3 pages, 4 figures. Submitted to JAP for 58th MMM Proceeding
Energy-efficient domain wall motion governed by the interplay of helicity-dependent optical effect and spin-orbit torque
Spin-orbit torque provides a powerful means of manipulating domain walls
along magnetic wires. However, the current density required for domain wall
motion is still too high to realize low power devices. Here we experimentally
demonstrate helicity-dependent domain wall motion by combining synchronized
femtosecond laser pulses and short current pulses in Co/Ni/Co ultra-thin film
wires with perpendicular magnetization. Domain wall can remain pinned under one
laser circular helicity while depinned by the opposite circular helicity.
Thanks to the all-optical helicity-dependent effect, the threshold current
density due to spin-orbit torque can be reduced by more than 50%. Based on this
joint effect combining spin-orbit torque and helicity-dependent laser pulses,
an optoelectronic logic-in-memory device has been experimentally demonstrated.
This work enables a new class of low power spintronic-photonic devices beyond
the conventional approach of all-optical switching or all-current switching for
data storage.Comment: 21 pages, 5 figure
Ultrafast and terahertz spintronics: Guest editorial
Spin-based electronics (spintronics) aims at extending electronic functionalities, which rely on the electron charge as information carrier, by the spin of the electron. To make spintronics competitive and compatible with other information carriers like photons and electrons, their speed needs to be pushed to femtosecond time scales and, thus, terahertz frequencies. In ultrafast and terahertz spintronics, femtosecond optical and terahertz electromagnetic pulses are used to induce spin torque and spin transport and to monitor the subsequent time evolution. The two approaches, sometimes referred to as femto-magnetism and terahertz magnetism, have provided new, surprising, and relevant insight as well as applications for spintronics. Examples include the ultrafast optical switching of magnetic order and the generation of broadband terahertz electromagnetic fields. This APL Special Topic Collection is dedicated to provide a platform for the newest developments and future trends in the very active, dynamic, and exciting research field of ultrafast and terahertz spintronics
Light-induced magnetization reversal of high-anisotropy TbCo alloy films
Magnetization reversal using circularly polarized light provides a new way to
control magnetization without any external magnetic field and has the potential
to revolutionize magnetic data storage. However, in order to reach ultra-high
density data storage, high anisotropy media providing thermal stability are
needed. Here, we evidence all-optical magnetization switching for different
TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching
for films with anisotropy fields reaching 6 T corresponding to anisotropy
constants of 3x106 ergs/cm3. Optical magnetization switching is observed only
for alloys which compensation temperature can be reached through sample
heating
Bringing depth to scanning tunnelling microscopy: subsurface vision of buried nano-objects in metals
A method for subsurface visualization and characterization of hidden
subsurface nano-structures based on Scanning Tuneling Microscopy/Spectroscopy
(STM/STS) has been developed. The nano-objects buried under a metal surface up
to several tens of nanometers can be visualized through the metal surface and
characterized with STM without destriying the sample. This non-destructive
method exploits quantum well (QW) states formed by partial electron confinement
between the surface and buried nano-objects. The specificity of STM allows for
nano-objects to be singled out and easily accessed. Then, their shape, size and
burial depth can be determined by analysing the spatial distribution and
oscillatory behavior of the electron density at the surface of the sample. The
proof of concept was demonstrated by fabricating argon nanoclusters embedded
into a single-crystalline Cu matrix. Taking advantage of the specific
electronic band structure Cu and inner electron focusing, we experimentally
demonstrated that noble-gas nanoclusters of several nanometers large buried as
deep as 80 nm can be detected, characterized and imaged. The ultime depth of
this ability is estimated as 110 nm. This approach using QW states paves the
way for an enhanced 3D characterization of nanostructures hidden well below a
metallic surface.Comment: Submitted in Nanoscale Horizon
Domain-wall motion induced by spin transfer torque delivered by helicity-dependent femtosecond laser
In magnetic wires with perpendicular anisotropy, moving domain with only
current or only circularly polarized light requires a high power. Here, we
propose to reduce it by using both short current pulses and femtosecond laser
pulses simultaneously. The wires were made out of perpendicularly magnetized
film of Pt/Co/Ni/Co/Pt. The displacement of the domain wall is found to be
dependent on the laser helicity. Based on a quantitative analysis of the
current-induced domain wall motion, the spin orbit torque contribution can be
neglected when compared to the spin transfer torque contribution. The effective
field of the spin transfer torque is extracted from the pulsed field domain
wall measurements. Finally, our result can be described using the
Fatuzzo-Labrune model and considering the effective field due to the polarized
laser beam, the effective field due to spin transfer torque, and the Gaussian
temperature distribution of the laser spot.Comment: 14 pages, 4 figure
Genetic control of plasticity of oil yield for combined abiotic stresses using a joint approach of crop modeling and genome-wide association
Understanding the genetic basis of phenotypic plasticity is crucial for
predicting and managing climate change effects on wild plants and crops. Here,
we combined crop modeling and quantitative genetics to study the genetic
control of oil yield plasticity for multiple abiotic stresses in sunflower.
First we developed stress indicators to characterize 14 environments for
three abiotic stresses (cold, drought and nitrogen) using the SUNFLO crop model
and phenotypic variations of three commercial varieties. The computed plant
stress indicators better explain yield variation than descriptors at the
climatic or crop levels. In those environments, we observed oil yield of 317
sunflower hybrids and regressed it with three selected stress indicators. The
slopes of cold stress norm reaction were used as plasticity phenotypes in the
following genome-wide association study.
Among the 65,534 tested SNP, we identified nine QTL controlling oil yield
plasticity to cold stress. Associated SNP are localized in genes previously
shown to be involved in cold stress responses: oligopeptide transporters, LTP,
cystatin, alternative oxidase, or root development. This novel approach opens
new perspectives to identify genomic regions involved in
genotype-by-environment interaction of a complex traits to multiple stresses in
realistic natural or agronomical conditions.Comment: 12 pages, 5 figures, Plant, Cell and Environmen
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