125 research outputs found
Ultrafast magnetization switching by spin-orbit torques
Spin-orbit torques induced by spin Hall and interfacial effects in heavy
metal/ferromagnetic bilayers allow for a switching geometry based on in-plane
current injection. Using this geometry, we demonstrate deterministic
magnetization reversal by current pulses ranging from 180~ps to ms in
Pt/Co/AlOx dots with lateral dimensions of 90~nm. We characterize the switching
probability and critical current as function of pulse length, amplitude,
and external field. Our data evidence two distinct regimes: a short-time
intrinsic regime, where scales linearly with the inverse of the pulse
length, and a long-time thermally assisted regime where varies weakly.
Both regimes are consistent with magnetization reversal proceeding by
nucleation and fast propagation of domains. We find that is a factor 3-4
smaller compared to a single domain model and that the incubation time is
negligibly small, which is a hallmark feature of spin-orbit torques
Symmetry and magnitude of spin-orbit torques in ferromagnetic heterostructures
Current-induced spin torques are of great interest to manipulate the
orientation of nanomagnets without applying external magnetic fields. They find
direct application in non-volatile data storage and logic devices, and provide
insight into fundamental processes related to the interdependence between
charge and spin transport. Recent demonstrations of magnetization switching
induced by in-plane current injection in ferromagnetic heterostructures have
drawn attention to a class of spin torques based on orbital-to-spin momentum
transfer, which is alternative to pure spin transfer torque (STT) between
noncollinear magnetic layers and amenable to more diversified device functions.
Due to the limited number of studies, however, there is still no consensus on
the symmetry, magnitude, and origin of spin-orbit torques (SOTs). Here we
report on the quantitative vector measurement of SOTs in Pt/Co/AlO trilayers
using harmonic analysis of the anomalous and planar Hall effects as a function
of the applied current and magnetization direction. We provide an all-purpose
scheme to measure the amplitude and direction of SOTs for any arbitrary
orientation of the magnetization, including corrections due to the interplay of
Hall and thermoelectric effects. Based on general space and time inversion
symmetry arguments, we show that asymmetric heterostructures allow for two
different SOTs having odd and even behavior with respect to magnetization
reversal. Our results reveal a scenario that goes beyond established models of
the Rashba and spin Hall contributions to SOTs. The even SOT is STT-like but
stronger than expected from the spin Hall effect in Pt. The odd SOT is composed
of a constant field-like term and an additional component, which is strongly
anisotropic and does not correspond to a simple Rashba field.Comment: Supplementary Informations follows Paper in the .pdf fil
Chirality-induced asymmetric magnetic nucleation in Pt/Co/AlOx ultrathin microstructures
The nucleation of reversed magnetic domains in Pt/Co/AlO
microstructures with perpendicular anisotropy was studied experimentally in the
presence of an in-plane magnetic field. For large enough in-plane field,
nucleation was observed preferentially at an edge of the sample normal to this
field. The position at which nucleation takes place was observed to depend in a
chiral way on the initial magnetization and applied field directions. An
explanation of these results is proposed, based on the existence of a sizable
Dzyaloshinskii-Moriya interaction in this sample. Another consequence of this
interaction is that the energy of domain walls can become negative for in-plane
fields smaller than the effective anisotropy field.Comment: Published version, Physical Review Letters 113, 047203 (2014
Direct Observation of Massless Domain Wall Dynamics in Nanostripes with Perpendicular Magnetic Anisotropy
Domain wall motion induced by nanosecond current pulses in nanostripes with
perpendicular magnetic anisotropy (Pt/Co/AlO) is shown to exhibit
negligible inertia. Time-resolved magnetic microscopy during current pulses
reveals that the domain walls start moving, with a constant speed, as soon as
the current reaches a constant amplitude, and no or little motion takes place
after the end of the pulse. The very low 'mass' of these domain walls is
attributed to the combination of their narrow width and high damping parameter
. Such a small inertia should allow accurate control of domain wall
motion, by tuning the duration and amplitude of the current pulses
Chiral damping of magnetic domain walls
Structural symmetry breaking in magnetic materials is responsible for a
variety of outstanding physical phenomena. Examples range from the existence of
multiferroics, to current induced spin orbit torques (SOT) and the formation of
topological magnetic structures. In this letter we bring into light a novel
effect of the structural inversion asymmetry (SIA): a chiral damping mechanism.
This phenomenon is evidenced by measuring the field driven domain wall (DW)
motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The
difficulty in evidencing the chiral damping is that the ensuing DW dynamics
exhibit identical spatial symmetry to those expected from the
Dzyaloshinskii-Moriya interaction (DMI). Despite this fundamental resemblance,
the two scenarios are differentiated by their time reversal properties: while
DMI is a conservative effect that can be modeled by an effective field, the
chiral damping is purely dissipative and has no influence on the equilibrium
magnetic texture. When the DW motion is modulated by an in-plane magnetic
field, it reveals the structure of the internal fields experienced by the DWs,
allowing to distinguish the physical mechanism. The observation of the chiral
damping, not only enriches the spectrum of physical phenomena engendered by the
SIA, but since it can coexists with DMI it is essential for conceiving DW and
skyrmion devices
Kinematic differences between left- and right-handed cricket fast bowlers during the bowling action
Background: Despite differences between left- and right-handed athletes in other sports, minimal evidence exists regarding biomechanical similarities and differences between left- and right-handed cricket fast bowlers performing an equivalent task.
Objectives: This study aimed to compare the kinematics between left and right-handed fast bowlers performing an equivalent task (i.e. bowling ‘over the wicket’ to a batter of the same handedness as the bowler).
Methods: Full body, three-dimensional kinematic data for six left-handed and 20 right-handed adolescent, male, fast bowlers were collected using the Xsens inertial measurement system. Time-normalised joint and segment angle time histories from back foot contact to follow-through ground contacts were compared between groups via statistical parametric mapping. Whole movement and subphase durations were also compared.
Results: Left-handed players displayed significantly more trunk flexion from 49%-56% of the total movement (ball release occurred at 54%; p = 0.037) and had shorter back foot contact durations on average (0.153 vs 0.177 s; p = 0.036) compared to right-handed players.
Conclusion: Left- and right-handed bowlers displayed similar sagittal plane kinematics but appeared to use non-sagittal plane movements differently around the time of ball release. The kinematic differences identified in this study can inform future research investigating the effect of hand dominance on bowling performance and injury risk
Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers
We present a comprehensive study of the current-induced spin-orbit torques in
perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in
steps up to 300 degrees C and characterized using x-ray absorption
spectroscopy, transmission electron microscopy, resistivity, and Hall effect
measurements. By performing adiabatic harmonic Hall voltage measurements, we
show that the transverse (field-like) and longitudinal (antidamping-like)
spin-orbit torques are composed of constant and magnetization-dependent
contributions, both of which vary strongly with annealing. Such variations
correlate with changes of the saturation magnetization and magnetic anisotropy
and are assigned to chemical and structural modifications of the layers. The
relative variation of the constant and anisotropic torque terms as a function
of annealing temperature is opposite for the field-like and antidamping
torques. Measurements of the switching probability using sub-{\mu}s current
pulses show that the critical current increases with the magnetic anisotropy of
the layers, whereas the switching efficiency, measured as the ratio of magnetic
anisotropy energy and pulse energy, decreases. The optimal annealing
temperature to achieve maximum magnetic anisotropy, saturation magnetization,
and switching efficiency is determined to be between 240 degrees and 270
degrees C
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