53 research outputs found
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
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
Earthquake-like dynamics in ultrathin magnetic film
We study the motion of a domain wall on an ultrathin magnetic film using the
magneto-optical Kerr effect (MOKE). At tiny magnetic fields, the wall creeps
only via thermal activation over the pinning centers present in the sample. Our
results show that this creep dynamics is highly intermittent and correlated. A
localized instability triggers a cascade, akin to aftershocks following a large
earthquake, where the pinned wall undergoes large reorganizations in a compact
active region for a few seconds. Surprisingly, the size and shape of these
reorganizations display the same scale-free statistics of the depinning
avalanches in agreement with the quenched Kardar-Parisi-Zhang universality
class.Comment: 5 pages, 4 figure
Spin-orbit torques for current parallel and perpendicular to a domain wall
We report field- and current-induced domain wall (DW) depinning experiments
in Ta/Co20Fe60B20/MgO nanowires through a Hall cross geometry. While purely
field-induced depinning shows no angular dependence on in-plane fields, the
effect of the current depends crucially on the internal DW structure, which we
manipulate by an external magnetic in-plane field. We show for the first time
depinning measurements for a current sent parallel to the DW and compare its
depinning efficiency with the conventional case of current flowing
perpendicularly to the DW. We find that the maximum efficiency is similar for
both current directions within the error bars, which is in line with a
dominating damping-like spin-orbit torque (SOT) and indicates that no large
additional torques arise for currents parallel to the DW. Finally, we find a
varying dependence of the maximum depinning efficiency angle for different DWs
and pinning levels. This emphasizes the importance of our full angular scans
compared to previously used measurements for just two field directions
(parallel and perpendicular to the DW) and shows the sensitivity of the
spin-orbit torque to the precise DW structure and pinning sites.Comment: 11 pages, 3 figure
Enhancing All-Optical Switching of Magnetization by He Ion Irradiation
All-optical switching (AOS) of magnetization by a single femtosecond laser pulse in Co/Gd based synthetic ferrimagnets is the fastest magnetization switching process. On the other hand, He ion irradiation has become a promising tool for interface engineering of spintronic material platforms, giving rise to significant modification of magnetic properties. In this paper, we explore the use of He ion irradiation to enhance single pulse AOS of Co/Gd bilayer-based synthetic ferrimagnets. The intermixing of the constituent magnetic layers by He ion irradiation was both numerically simulated and experimentally verified. We theoretically modelled the effects of intermixing on AOS using the layered microscopic 3-temperature model and found that AOS is enhanced significantly by breaking the pristine Co/Gd interface through intermixing. Following this notion, we studied the threshold fluence of AOS as a function of He ion irradiation fluence. We found that the AOS threshold fluence can be reduced by almost 30%. Our study reveals the control of AOS by He ion irradiation, which opens up an industrially compatible approach for local AOS engineering
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