8 research outputs found
All-optical switching of magnetic domains in Co/Gd heterostructures with Dzyaloshinskii-Moriya Interaction
Given the development of hybrid spintronic-photonic devices and chiral
magnetic structures, a combined interest in all-optical switching (AOS) of
magnetization and current-induced domain wall motion in synthetic ferrimagnetic
structures with strong Dzyaloshinskii-Moriya Interaction (DMI) is emerging. In
this study, we report a study on single-pulse all-optical toggle switching and
asymmetric bubble expansion in specially engineered Co/Gd-based multilayer
structures. In the absence of any external magnetic fields, we look into the
AOS properties and the potential role of the DMI on the AOS process as well as
the stability of optically written micro-magnetic domains. Particularly,
interesting dynamics are observed in moon-shaped structures written by two
successive laser pulses. The stability of domains resulting from an interplay
of the dipolar interaction and domain-wall energy are compared to simple
analytical models and micromagnetic simulations
Exploring THz exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents
Using spin currents generated by fs laser pulses, we demonstrate excitation
of GHz ferromagnetic resonance and THz ferrimagnetic exchange resonances in
Co/Gd/Co/Gd multilayers by time-resolved magneto-optic Kerr effect
measurements. Varying the Gd layer thickness allows for a tuning of the
resonance spectrum by manipulating the total angular momentum and strength of
effective exchange fields between the antiferromagnetically coupled layers.
Close to the compensation point of angular momentum, a minimum in the frequency
of the exchange-dominated mode and a maximum in the frequency of the
ferromagnetic resonance mode is observed. Finally, to gain better understanding
of the excitation mechanism, we analyze the anomalous variation in the measured
exchange mode amplitude as a function of its frequency. A peak in this
amplitude in the vicinity of the compensation point of angular momentum is
explained using a macrospin model, taking nonlinear effects at finite
precession amplitudes into account
Towards high all-optical data writing rates in synthetic ferrimagnets
Although all-optical magnetization switching with fs laser pulses has
garnered much technological interest, the ultimate data rates achievable have
scarcely been investigated. Recently it has been shown that after a switching
event in a GdCo alloy, a second laser pulse arriving 7 ps later can
consistently switch the magnetization. However, it is as of yet unknown whether
the same holds in layered ferrimagnetic systems, which hold much promise for
applications. In this work we investigate the minimum time delay required
between two subsequent switching events in synthetic ferrimagnetic Co/Gd
bilayers using two fs laser pulses. We experimentally demonstrate that the
minimum time delay needed for consistent switching can be as low as 10 ps.
Moreover, we demonstrate the importance of engineering heat diffusion away from
the magnetic material, as well as control over the laser pulse power. This
behavior is reproduced using modelling, where we find that the second switch
can occur even when the magnetization is not fully recovered. We further
confirm that heat diffusion is a critical factor in reducing the time delay for
the second switch, while also confirming a critical dependence on laser power
Deterministic all-optical magnetization writing facilitated by non-local transfer of spin angular momentum
Ever since the discovery of all-optical magnetization switching (AOS) around
a decade ago, this phenomenon of manipulating magnetization using only
femtosecond laser pulses has promised a large potential for future data storage
and logic devices. Two distinct mechanisms have been observed, where the final
magnetization state is either defined by the helicity of many incoming laser
pulses, or toggled by a single pulse. What has thus far been elusive, yet
essential for applications, is the deterministic writing of a specific
magnetization state with a single laser pulse. In this work we experimentally
demonstrate such a mechanism by making use of a spin polarized current which is
optically generated in a ferromagnetic reference layer, assisting or hindering
switching in an adjacent Co/Gd bilayer. We show deterministic writing of an
'up' and 'down' state using a sequence of 1 or 2 pulses, respectively.
Moreover, we demonstrate the non-local origin of the effect by varying the
magnitude of the generated spin current. Our demonstration of deterministic
magnetization writing could provide an essential step towards the
implementation of future optically addressable spintronic memory devices
Ultrafast single-pulse all-optical switching in synthetic ferrimagnetic Tb/Co/Gd multilayers
In this work, we investigate single-shot all-optical switching (AOS) in
Tb/Co/Gd/Co/Tb multilayers in an attempt to establish AOS in synthetic
ferrimagnets with high magnetic anisotropy. In particular, we study the effect
of varying Tb thicknesses to disentangle the role of the two rare earth
elements. Even though the role of magnetic compensation has been considered to
be crucial, we find that the threshold fluence for switching is largely
independent of the Tb content. Moreover, we identify the timescale for the
magnetization to cross zero to be within the first ps after laser excitation
using time-resolved MOKE. We conclude that the switching is governed mostly by
interactions between Co and Gd
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.Comment: 18 pages, 3 figure
Field-free spin orbit torque switching of synthetic antiferromagnet through interlayer Dzyaloshinskii-Moriya interaction
Perpendicular synthetic antiferromagnets (SAFs) are of interest for the next
generation ultrafast, high density spintronic memory and logic devices.
However, to energy efficiently operate their magnetic order by current-induced
spin orbit torques (SOTs), an unfavored high external field is conventionally
required to break the symmetry. Here, we theoretically and experimentally
demonstrate the field-free SOT switching of a perpendicular SAF through the
introduction of interlayer Dzyaloshinskii-Moriya interaction (DMI). By
macro-spin simulation, we show that the speed of field-free switching increases
with the in-plane mirror asymmetry of injected spins. We experimentally observe
the existence of interlayer DMI in our SAF sample by an azimuthal angular
dependent anomalous Hall measurement. Field-free switching is accomplished in
such a sample and the strength of the effective switching field demonstrates
its origin from interlayer DMI. Our results provide a new strategy for SAF
based high performance SOT devices