Application concepts for ultrafast laser-induced
skyrmion creation and annihilation
Cite as: Appl. Phys. Lett. 118, 192403 (2021); doi: 10.1063/5.0046033
Submitted: 31 January 2021 .Accepted: 26 March 2021 .
Published Online: 11 May 2021
Kathinka Gerlinger,
1
Bastian Pfau,
1,a)
Felix B€
uttner,
2,3
Michael Schneider,
1
Lisa-Marie Kern,
1
Josefin Fuchs,
1
Dieter Engel,
1
Christian M. G€
unther,
4,5
Mantao Huang,
3
Ivan Lemesh,
3
Lucas Caretta,
3
Alexandra Churikova,
3
Piet Hessing,
1
Christopher Klose,
1
Christian Str€
uber,
1,b)
Clemens von Korff Schmising,
1
Siying Huang,
3
Angela Wittmann,
3
Kai Litzius,
3
Daniel Metternich,
2
Riccardo Battistelli,
2
Kai Bagschik,
6
Alexandr Sadovnikov,
7
Geoffrey S. D. Beach,
3
and Stefan Eisebitt
1,5
AFFILIATIONS
1
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
2
Helmholtz-Zentrum Berlin, 14109 Berlin, Germany
3
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
4
Zentraleinrichtung Elektronenmikroskopie (ZELMI), Technische Universit€
at Berlin, 10623 Berlin, Germany
5
Institut f€
ur Optik und Atomare Physik, Technische Universit€
at Berlin, 10623 Berlin, Germany
6
Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany
7
Saratov State University, Saratov 410012, Russia
Note: This paper is part of the APL Special Collection on Mesoscopic Magnetic Systems: From Fundamental Properties to Devices.
a)
Author to whom correspondence should be addressed: bastian.pfau@mbi-berlin.de
b)
Department of Physics, Freie Universit€
at Berlin, 14195 Berlin, Germany
ABSTRACT
Magnetic skyrmions can be created and annihilated in ferromagnetic multilayers using single femtosecond infrared laser pulses above a
material-dependent fluence threshold. From the perspective of applications, optical control of skyrmions offers a route to a faster and, poten-
tially, more energy-efficient new class of information-technology devices. Here, we investigate laser-induced skyrmion generation in two dif-
ferent materials, mapping out the dependence of the process on the applied field and the laser fluence. We observe that sample properties
like strength of the Dzyaloshinskii–Moriya interaction and pinning do not considerably influence the initial step of optical creation. In con-
trast, the number of skyrmions created can be directly and robustly controlled via the applied field and the laser fluence. Based on our find-
ings, we propose concepts for applications, such as all-optical writing and deletion, an ultrafast skyrmion reshuffling device for probabilistic
computing, and a combined optical and spin–orbit torque-controlled racetrack.
V
C2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://
creativecommons.org/licenses/by/4.0/).https://doi.org/10.1063/5.0046033
Since the discovery of room-temperature-stable isolated magnetic
skyrmions with a chirality stabilized by interfacial Dzyaloshinskii–
Moriya interaction (DMI) in ferromagnetic multilayers,
1–4
the use of
these topological solitons has been discussed for data memory, storage,
and processing applications.
5–8
Shifting, writing, and deleting opera-
tions were already efficiently realized exploiting spin–orbit torques
(SOT) generated from spin-polarized current pulses of ns or sub-ns
duration.
2,9–12
Femtosecond optical laser pulses offer an alternative
way of manipulating magnetization at even shorter timescales and,
potentially, with higher energy efficiency,
13
in particular when focused
to a nanometer-scale spot.
14
Several groups recently reported that sky-
rmions form in ferromagnetic multilayers after irradiation with a sin-
gle fs laser pulse.
15–17
The optical nucleation mechanism was
uncovered by time-resolved x-ray scattering in concert with atomistic
simulations:
16
thefslaserpulseexcitesthesampleintoahigh-
temperature fluctuation state that largely reduces the topological energy
barrier leading to the nucleation of skyrmions on a ps timescale. This
nucleation is followed by coarsening of the skyrmions to their equilib-
rium size and density during cooldown of the sample. Remarkably,
laser nucleation of skyrmions is found in two materials that are already
Appl. Phys. Lett. 118, 192403 (2021); doi: 10.1063/5.0046033 118, 192403-1
V
CAuthor(s) 2021
Applied Physics Letters ARTICLE scitation.org/journal/apl
considered in the research of magnetic device applications, namely Co/
Pt multilayers
18
and Pt/CoFeB/MgO multilayers,
5,6,8–10
which makes
laser control of nanometer-scale skyrmions attractive as an integral
component in device concepts.
In the present work, we investigate optical skyrmion creation
from the perspective of device applications in these two materials.
Both multilayers are similar with respect to saturation magnetization
and strength of the perpendicular magnetic anisotropy. As a result,
both multilayers form a labyrinth of elongated domains with
nanometer-scale width (stripe domains) at remanence resulting in a
characteristically sheared hysteresis loop. However, the materials differ
in their DMI strength: due to its sizeable DMI, Pt/CoFeB/MgO can
host Ne
el-type skyrmions at room temperature.
2,10,19
In contrast, the
domain walls in Co/Pt are predominately Bloch-type
16
as the DMI is
negligible in this inversion-symmetric multilayer.
We investigate and compare laser-induced skyrmion creation in
both materials by varying the applied out-of-plane magnetic field and
the fluence of the infrared (IR) laser. We particularly analyze the den-
sity of skyrmion patterns created as well as correlations in the patterns.
Surprisingly, we find that neither of these properties qualitatively
changes with the presence or absence of DMI or pinning in the mate-
rial. Most importantly, applied field and laser fluence allow for direct
and robust control of the skyrmion creation, including a so far undis-
covered annihilation regime. Based on this control, we propose first
concepts to implement optical skyrmion creation in applications
toward devices.
The experiments were conducted using Ta(3.6)/Pt(3.7)/[Pt(2.7)/
Co
60
Fe
20
B
20
(0.9)/MgO(1.5)]
15
/Pt(2.7) multilayers (thicknesses in nm)
and Ta(3)/[Co(0.6)/Pt(0.8)]
15
/Ta(2) multilayers. Both multilayers were
deposited on silicon-nitride membranes (thickness 700 nm and 150 nm,
respectively) by magnetron sputtering. During deposition, the argon
pressure was adjusted to 2:7103mbar for Co/Pt and 4 103mbar
for Pt/CoFeB/MgO (4:7103mbar for Pt). The Pt/CoFeB/MgO films
were structured into 1.5–3 lm long and 0.9–1.4 lmwidestriplinesfor
current injection by liftoff electron-beam lithography and focused ion
beam (FIB) milling. We produced several samples with nominally identi-
cal composition. The results presented in this Letter were obtained from
two Co/Pt samples and five Pt/CoFeB/MgO samples.
For Pt/CoFeB/MgO, a sizable DMI on the order of 1.8 m Jm
2
was previously reported
19
arising from the asymmetric interfaces of
CoFeB. Due to the symmetric stacking, interface DMI contributions in
Co/Pt are expected to cancel to first approximation.
3
The magnetic hysteresis of both multilayers was measured by
magneto-optical Kerr effect (MOKE) magnetometry. In the case of
Co/Pt [Fig. 1(a)], we used a sister sample grown on a float glass sub-
strate. The hysteresis of the Pt/CoFeB/MgO samples was determined
on the actual striplines using a focused MOKE setup. A representative
loop is shown in Fig. 1(b). The other Pt/CoFeB/MgO samples exhibit
similarshearedhysteresisloopsasshowninFig. 1(b), with slightly
varying saturation fields in the range of 45–65 mT due to tiny
position-dependent thickness variations during the sputter deposition
process.
We imaged the samples using soft x-ray Fourier-transform
holography
20,21
in transmission via a standard soft x-ray holography
mask, fabricated on the backside of the membrane using FIB milling,
with a 1–1.5 lm field of view (FOV) and reference holes allowing for
30–40 nm spatial resolution.
The holography experiments were conducted at beamline P04 at
the synchrotron-radiation source PETRA III (Hamburg, Germany)
using circularly polarized, coherent soft x-rays tuned to the cobalt L
3
edge (780 eV) to achieve magnetic contrast based on the x-ray mag-
netic circular dichroism. An in situ 1030 nm fiber laser was focused on
the samples to a spot size of 60 63 lm
2
(full width at half maxi-
mum).AsthissizeismuchlargerthantheFOV,allfluencesaregiven
FIG. 1. Optical skyrmion creation as a function of the out-of-plane magnetic field.
(a) and (b) Hysteresis curve of (a) a Co/Pt and (b) a Pt/CoFeB/MgO sample mea-
sured by MOKE (blue lines) and by holographic imaging (blue data points). Orange
data points indicate the magnetization retrieved from images after irradiation with a
single laser pulse. Inset images show selected examples of initial and final state
pairs. The inset graph in (b) shows a single-skyrmion creation–annihilation cycle. (i)
Saturated initial state, (ii) laser-induced creation of a skyrmion, (iii) same skyrmion
at increased B
z
, (iv) laser-induced annihilation. (c) and (d) Skyrmion density qSk
after single-laser pulse irradiation of (c) Co/Pt and (d) Pt/CoFeB/MgO. The line rep-
resents a linear fit to the data points. (a) and (c) were measured with the same
sample, (b) and (d) with different samples of the same material.
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CAuthor(s) 2021
as peak fluence of a Gaussian profile where a systematic error of up to
25% (uncertainty of the focus plane position) and a statistical error of
10% (uncertainty and drift of the sample–laser overlap) have to be
considered. An out-of-plane magnetic field at the sample was applied
using an electromagnet. As a typical experimental procedure, we
imaged the magnetic state of the sample after (i) saturating the sample
in a magnetic field of 6270 mT, (ii) reducing the field to a desired
value, and (iii) applying a single 250 fs long IR laser pulse to nucleate
skyrmions in the sample.
From the images of the samples’ out-of-plane magnetization com-
ponent (for examples, see Figs. 1 and 2), we determined the number
and individual positions of the skyrmions created as well as the net mag-
netization within our FOV. To this end, we created binary images of
up and down magnetization from the holography images using image
segmentation based on Otsu’s method.
22
The effective diameter dof a
skyrmion was determined from its occupied area Aas d¼2ffiffiffiffiffiffiffiffiffi
A=p
p.
We estimate the error to be 62pixels(20 nm), which accounts for
our imaging resolution and errors from the image segmentation.
We find that skyrmions can be created in both materials after
irradiation with a single suitably intense laser pulse, see Figs. 1(a) and
1(b) and Ref. 16, where the same or sister samples have been
investigated, for the proof that they are skyrmions. To study the pro-
cess at different initial states in the hysteresis, we recorded sets of
images before and after irradiation with a single laser pulse of 19 mJ
cm
2
at different applied fields. We distinguish four regimes of the
process [inset images in Figs. 1(a) and 1(b) show prominent exam-
ples]. In the first regime, we create disordered configurations of skyrm-
ions from an initially saturated state. Here, the final states always
contain only skyrmions. We observe that the final skyrmion density in
both samples is directly controlled via the applied field, allowing to
cover the range from dense arrays down to single skyrmions in the
FOV [Figs. 1(c) and 1(d)]. Importantly, in this regime, we find a linear
relationship between skyrmion density and applied field for both mate-
rials. In the second regime, when starting from a stripe-domain state,
mixed states of skyrmions coexisting with stripe domains appear after
laser exposure in Co/Pt. In contrast, pure skyrmion states are still cre-
ated in Pt/CoFeB/MgO, probably stabilized by the sizeable DMI in this
multilayer. At remanence (third regime), without a symmetry-breaking
field, the system remains in a pure stripe-domain state even after pow-
erful laser irradiation (see Ref. 16). Close to saturation (fourth regime),
we find the opposite process to skyrmion creation: a single laser pulse
annihilates skyrmions and stripe domains. The graph inset of Fig. 1(b)
illustrates a scheme to realize all-optical skyrmion creation and annihi-
lation in a single device (corresponding images are shown as insets
i–iv). First, starting in a saturated state at 45 mT, we optically create a
single skyrmion (i!ii),thenweslightlyincreasethefieldto51mT
which still preserves the existing skyrmion (ii!iii), and finally we opti-
cally annihilate the skyrmion by a second laser pulse (iii!iv).
Investigating the fluence dependence of the optical skyrmion cre-
ation, we reproduce previous observations of a sharp fluence threshold
in both samples [Figs. 2(a) and 2(b)]. Below the sample-specific
threshold, skyrmions do not nucleate or only after thousands of laser
pulses.
16
At the threshold, the skyrmion density rapidly increases with
the fluence and saturates at higher fluences. The reason for this behav-
ior is that skyrmions are nucleated in a high-temperature fluctuation
phase, a process that is independent of the fluence above a threshold
value.
16
After a subsequent coarsening phase during cooldown, the
skyrmions’ equilibrium density is determined by the applied field.
The threshold for both samples is very similar with 13 mJ cm
2
for
Co/Pt and 11 mJ cm
2
for Pt/CoFeB/MgO.
For applications, a narrow distribution of skyrmion diameters is
desirable, in particular, if the readout relies on the anomalous Hall
effect.
23
In Figs. 2(c) and 2(e), we show the diameter distribution for
the threshold and saturation regime corresponding to the insets in
Figs. 2(a) and 2(b). The mean (
d) and standard deviation (r
d
)ofthe
distribution are plotted for all fluences in Figs. 2(d) and 2(f).The
skyrmions are generally smaller in Co/Pt (
d¼55–80 nm) than in
Pt/CoFeB/MgO (
d¼130–215 nm) which is a result of the sample-
specific interplay of all magnetization-related energies.
11
In both sam-
ples, the diameter distribution of the laser-induced skyrmions is
almost independent of the laser fluence. Only at very low fluences,
closer to the fluence threshold, the skyrmions grow larger. As main
difference between both materials, the normalized diameter variation
rd=
dis broader in Co/Pt (0.41) than in Pt/CoFeB/MgO (0.23).
This difference may be related to the different pinning in both
samples. Co/Pt multilayers typically exhibit a high density of pinning
sites due to grain boundaries and different grain orientation in the
polycrystalline material.
24,25
On the contrary, CoFeB layers grow in an
FIG. 2. Optical skyrmion creation as a function of the laser fluence. (a) and (b)
Average skyrmion density after illuminating a magnetically saturated state with a
single laser pulse in (a) Co/Pt (at 59 mT) and (b) Pt/CoFeB/MgO (at 20 mT). The
data are based on (a) 68 images and (b) 20 images. For multiple measurements,
error bars indicate their standard deviation. Inset images show two examples at low
and high fluence. (c) and (e) Distribution of skyrmion diameter at low and high flu-
ence as marked by color. (d) and (f) Average skyrmion diameter
d(data points)
and width of the distribution (r
d
) (filled area).
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CAuthor(s) 2021
amorphous way with low pinning density.
2,9,26,27
In the coarsening
phase of the optical skyrmion creation process,
16
the higher pinning in
Co/Pt could lead to an inhomogeneous growth of the skyrmions.
An important aspect for the application of skyrmion creation
mechanisms is if and how the positions of the skyrmions created are
defined in the multilayer film. For instance, natural and artificial pin-
ning sites were used to localize SOT-induced skyrmion nucleation.
10
We therefore investigate if pinning or pre-existing magnetic textures
influence the position of optically created skyrmions by evaluating
the statistical spatial distribution of nucleation sites. To this end,
we calculate the pair correlation between two binary images by
C¼hm1;m2i=ðjjm1jj jjm2jjÞ where h:;:idenotes the pixel-wise scalar
product and jj:jj is the corresponding norm. For m
1
and m
2
,weuse
the normalized (binary) magnetization in each pixel reduced by the
average magnetization in the FOV to account for a systematic correla-
tion offset arising for a non-zero net magnetization from the binariza-
tion of the magnetization to the values –1 or 1. Finally, we determine
the average of the correlations of all subsequent image pairs.
By applying this correlation analysis to independently created
skyrmion patterns (from the data used for Fig. 2), we search for pre-
ferred nucleation sites due to pinning (red data points in Fig. 3). For
Co/Pt, sufficient data are available for a fluence-resolved analysis; for
Pt/CoFeB/MgO, we summarize all data above the threshold to a single
correlation value. Additional sum images of the binary images illus-
trate the spatial distribution of nucleation sites. For both materials, we
find negligible correlation (C<0.1) reflecting an almost completely
random and homogeneous distribution of nucleation sites from which
we conclude that pinning does not play a role for the specific positions
of the skyrmions created. This finding is in line with the recently pro-
posed nucleation mechanism via a high-temperature fluctuation state
that dispenses with particular nucleation sites and promotes a random
distribution.
16
To investigate the influence of pre-existing magnetic textures, we
changed our experimental procedure. We started in a laser-generated
skyrmion state and reimaged it after each subsequent laser pulse with-
out saturating the sample in between. We recorded five images after
subsequent laser pulses per fluence and show the average correlation
in Fig. 3 as blue data points. Here, we find a different behavior than
before: at fluences above, but close to the nucleation threshold, the cor-
relation is very high, meaning that the initially created skyrmion pat-
tern is to a large extent reproduced after a subsequent laser pulse of
the same intensity. In contrast, at high fluences significantly exceeding
the nucleation threshold, the skyrmion positions become completely
uncorrelated and distribute almost homogeneously over the FOV.
This second, softer fluence threshold was missed in the previous stud-
ies of laser-induced skyrmion nucleation. We explain the memory
effect at lower fluence with an inhomogeneous excitation along the
depth of the sample due to the strong absorption of the IR in the mul-
tilayers. At low fluences, it seems likely that only the topmost layers
enter the fluctuation state while patterns in the lower layers, if present,
are not completely erased and subsequently serve as a guide for the
nucleation of the skyrmion state.
The full randomization of the skyrmion pattern at high laser flu-
ences promises a route to an interesting application of optical sky-
rmion writing: a skyrmion reshuffler
28,29
working on ultrafast
timescales in contrast to previous proposals based on skyrmion diffu-
sion.
5
A reshuffling device is a key component in probabilistic com-
puting for signal decorrelation. Correlated inputs to logic gates of
probabilistic computing lead to incorrect results. As the skyrmion den-
sity in the optical device is well controlled by the applied field only and
is independent of the laser fluence, a single laser shot sufficiently above
the skyrmion creation threshold may be used for reshuffling on the
sub-ns timescale.
Summarizing our observations, we find very similar properties of
both materials with respect to optical skyrmion creation, in spite of the
different strength of DMI and pinning in our samples. In both materi-
als, skyrmions are created after a single laser pulse of sufficient fluence
with a density that can be controlled via the applied field, down to the
generation of isolated skyrmions. At high fields, skyrmions can be
annihilated in both materials. Above the fluence threshold, skyrmion
diameter and density do not depend on the fluence anymore. The
nucleation is spatially homogeneous without any preferred nucleation
sites.
Although skyrmions can be created in both types of multilayers,
the inversion-asymmetry of the Pt/CoFeB/MgO system offers addi-
tional perspectives toward opto-spintronics applications. As illustrated
in Fig. 4, this material allows combining optical and SOT control of
skyrmions in a single device operated at a constant bias field. To dem-
onstrate this, we start with a saturated sample at Bz¼42 mT. At this
field, optical skyrmion creation is impossible in this specific sample.
However, a single, 4 ns long current pulse with a current density of
71011 Am
2sent through the strip line still creates a single sky-
rmionintheFOVviaSOT.
10
In the next step, we reduced the current
density below the SOT nucleation threshold and applied pulse trains
of positive and negative polarity to shift the skyrmion back and forth.
The skyrmion moves along the current direction with the typical incli-
nation resulting from the skyrmion Hall effect.
9,30
At the end of the
series, we annihilated the skyrmion with a single laser pulse. Note that
all the steps of skyrmion creation, displacement, and annihilation were
performed at constant external magnetic field facilitating application
in a device.
In conclusion, we demonstrate creation and annihilation of sky-
rmions for both kinds of ferromagnetic multilayers used in this study.
FIG. 3. Shot-to-shot correlation of created skyrmion patterns. Average correlation of
skyrmion patterns in (a) Co/Pt and (b) Pt/CoFeB/MgO. Red data points show the
average correlation of the data in Figs. 2(a) and 2(d) where the sample was satu-
rated after each pulse. Blue data points show the average of at least five binary
magnetization images after subsequent laser pulses without saturating the sample in
between [(a) at 83 mT and (b) at 20 mT]. Insets show corresponding sum images.
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CAuthor(s) 2021
The tunability of the skyrmion density by the external magnetic
field provides a critical parameter for skyrmion based applications.
The skyrmion density is largely insensitive to the laser fluence
above a material-dependent threshold. When laser-exposing an
existing skyrmion pattern, we find a strong memory effect of the
skyrmion positions at low fluences which almost completely
vanishes at high fluences leading to a random distribution. We
propose three application concepts based on these findings: an all-
optical skyrmion writer and deleter (Fig. 1), an ultrafast skyrmion
reshuffler for probabilistic computing (Fig. 3), and an opto-
spintronic skyrmion racetrack (Fig. 4).
We acknowledge DESY (Hamburg, Germany), a member of
the Helmholtz Association HGF, for the provision of experimental
facilities. Parts of this research were carried out at PETRA III
beamline P04. We thank M. Wieland and M. Drescher, Universit€
at
Hamburg, for providing us with their mobile laser hutch for the
experiments at PETRA III. Work at MIT was supported by the
DARPA TEE program. Devices were fabricated using equipment in
the MIT Microsystems Technology Laboratory and the MIT
Nanostructures Laboratory. Financial support from the Leibniz
Association via Grant No. K162/2018 (OptiSPIN), the Helmholtz
Young Investigator Group Program, as well as from the NSF
Graduate Research Fellowship Program, the GEM Consortium, Swiss
National Science Foundation and the Russian Ministry of Education
and Science (Project No. FSRR-2020-0005) is acknowledged.
DATA AVAILABILITY
The data that support the findings of this study are available
from the corresponding author upon reasonable request.
REFERENCES
1
W. Jiang, P. Upadhyaya, W. Zhang, G. Yu, M. B. Jungfleisch, F. Y. Fradin, J. E.
Pearson, Y. Tserkovnyak, K. L. Wang, O. Heinonen, S. G. Te Velthuis, and A.
Hoffmann, “Blowing magnetic skyrmion bubbles,” Science 349, 283–286
(2015).
2
S. Woo, K. Litzius, B. Kr€
uger, M. Y. Im, L. Caretta, K. Richter, M. Mann, A.
Krone, R. M. Reeve, M. Weigand, P. Agrawal, I. Lemesh, M. A. Mawass, P.
Fischer, M. Kl€
aui, and G. S. Beach, “Observation of room-temperature mag-
netic skyrmions and their current-driven dynamics in ultrathin metallic
ferromagnets,” Nat. Mater. 15, 501–506 (2016).
3
C. Moreau-Luchaire, C. Moutafis, N. Reyren, J. Sampaio, C. A. F. Vaz, N. Van
Horne, K. Bouzehouane, K. Garcia, C. Deranlot, P. Warnicke, P. Wohlh€uter,
J.-M. George, M. Weigand, J. Raabe, V. Cros, and A. Fert, “Additive interfacial
chiral interaction in multilayers for stabilization of small individual skyrmions
at room temperature,” Nat. Nanotechnol. 11, 444–448 (2016).
4
O. Boulle, J. Vogel, H. Yang, S. Pizzini, D. de Souza Chaves, A. Locatelli, T. O.
Mentes¸, A. Sala, L. D. Buda-Prejbeanu, O. Klein, M. Belmeguenai, Y.
Roussign
e, A. Stashkevich, S. M. Ch
erif, L. Aballe, M. Foerster, M. Chshiev, S.
Auffret, I. M. Miron, and G. Gaudin, “Room-temperature chiral magnetic sky-
rmions in ultrathin magnetic nanostructures,” Nat. Nanotechnol. 11, 449–454
(2016).
5
J. Z
azvorka, F. Jakobs, D. Heinze, N. Keil, S. Kromin, S. Jaiswal, K. Litzius, G.
Jakob, P. Virnau, D. Pinna, K. Everschor-Sitte, L. R
ozsa, A. Donges, U. Nowak,
and M. Kl€
aui, “Thermal skyrmion diffusion used in a reshuffler device,” Nat.
Nanotechnol. 14, 658–661 (2019).
6
S. Zhang, A. A. Baker, S. Komineas, and T. Hesjedal, “Topological computa-
tion based on direct magnetic logic communication,” Sci. Rep. 5, 15773 (2015).
7
A. Fert, V. Cros, and J. Sampaio, “Skyrmions on the track,” Nat. Nanotechnol.
8, 152–156 (2013).
8
R. Wiesendanger, “Nanoscale magnetic skyrmions in metallic films and multi-
layers: A new twist for spintronics,” Nat. Rev. Mater. 1, 16044 (2016).
9
K. Litzius, I. Lemesh, B. Kr€
uger, P. Bassirian, L. Caretta, K. Richter, F. B€
uttner,
K. Sato, O. A. Tretiakov, J. F€
orster, R. M. Reeve, M. Weigand, I. Bykova, H.
Stoll, G. Sch€utz, G. S. Beach, and M. Kla€ui, “Skyrmion Hall effect revealed by
direct time-resolved X-ray microscopy,” Nat. Phys. 13, 170–175 (2017).
10
F. B€
uttner, I. Lemesh, M. Schneider, B. Pfau, C. M. G€
unther, P. Hessing, J.
Geilhufe, L. Caretta, D. Engel, B. Kr€uger, J. Viefhaus, S. Eisebitt, and G. S.
Beach, “Field-free deterministic ultrafast creation of magnetic skyrmions by
spin-orbit torques,” Nat. Nanotechnol. 12, 1040–1044 (2017).
11
F. B€uttner, I. Lemesh, and G. S. Beach, “Theory of isolated magnetic skyrmions:
From fundamentals to room temperature applications,” Sci. Rep. 8, 4464
(2018).
12
S. Woo, K. M. Song, X. Zhang, M. Ezawa, Y. Zhou, X. Liu, M. Weigand, S.
Finizio, J. Raabe, M.-C. Park, K.-Y. Lee, J. W. Choi, B.-C. Min, H. C. Koo, and
J. Chang, “Deterministic creation and deletion of a single magnetic skyrmion
observed by direct time-resolved X-ray microscopy,” Nat. Electron. 1, 288–296
(2018).
13
C. D. Stanciu, F. Hansteen, A. V. Kimel, A. Kirilyuk, A. Tsukamoto, A. Itoh,
and T. Rasing, “All-optical magnetic recording with circularly polarized light,”
Phys. Rev. Lett. 99, 047601 (2007).
14
M. Finazzi, M. Savoini, A. R. Khorsand, A. Tsukamoto, A. Itoh, L. Du
o, A.
Kirilyuk, T. Rasing, and M. Ezawa, “Laser-induced magnetic nanostructures
with tunable topological properties,” Phys. Rev. Lett. 110, 177205 (2013).
15
S. G. Je, P. Vallobra, T. Srivastava, J. C. Rojas-S
anchez, T. H. Pham, M. Hehn,
G. Malinowski, C. Baraduc, S. Auffret, G. Gaudin, S. Mangin, H. B
ea, and O.
Boulle, “Creation of magnetic skyrmion bubble lattices by ultrafast laser in
ultrathin films,” Nano Lett. 18, 7362–7371 (2018).
16
F. B€
uttner, B. Pfau, M. B€
ottcher, M. Schneider, G. Mercurio, C. M. G€
unther, P.
Hessing, C. Klose, A. Wittmann, K. Gerlinger, L.-M. Kern, C. Str€uber, C. von
Korff Schmising, J. Fuchs, D. Engel, A. Churikova, S. Huang, D. Suzuki, I.
Lemesh, M. Huang, L. Caretta, D. Weder, J. H. Gaida, M. M€
oller, T. R. Harvey,
S. Zayko, K. Bagschik, R. Carley, L. Mercadier, J. Schlappa, A. Yaroslavtsev, L.
Le Guyarder, N. Gerasimova, A. Scherz, C. Deiter, R. Gort, D. Hickin, J. Zhu,
M. Turcato, D. Lomidze, F. Erdinger, A. Castoldi, S. Maffessanti, M. Porro, A.
Samartsev, J. Sinova, C. Ropers, J. H. Mentink, B. Dup
e, G. S. D. Beach, and S.
Eisebitt, “Observation of fluctuation-mediated picosecond nucleation of a topo-
logical phase,” Nat. Mater. 20, 30–37 (2021).
17
N. Novakovic-Marinkovic, M.-A. Mawass, O. Volkov, P. Makushko, W. D.
Engel, D. Makarov, and F. Kronast, “From stripes to bubbles: Deterministic
transformation of magnetic domain patterns in Co/Pt multilayers induced by
laser helicity,” Phys. Rev. B 102, 174412 (2020).
FIG. 4. Combined optical and SOT manipulation of a skyrmion in a magnetic strip
line. (a) Scanning electron micrograph of the Pt/CoFeB/MgO strip line. The circle
marks the FOV of holography imaging. Current pulses with density j
x
are injected
along the strip line. A constant bias field B
z
is applied in the out-of-plane direction.
The IR laser with fluence IIR impinges on the material under normal incidence. (b)
Sequence of images for skyrmion manipulation with SOT and fs laser pulses: (i)
after saturation the field is decreased to Bz¼42 mT, (ii) a skyrmion is created by
current pulse of jx¼71011 Am
2, (iii) and (iv) back and forth shifting of the sky-
rmion by current pulses of jx¼51011
–61011 Am
2of different polarity, (v)
annihilation of the skyrmion via a laser pulse of IIR ¼32 mJ cm
2
. In (iii)–(v), the
previous position of the skyrmion is marked by a colored circle.
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Appl. Phys. Lett. 118, 192403 (2021); doi: 10.1063/5.0046033 118, 192403-5
V
CAuthor(s) 2021
18
T. R. Albrecht, H. Arora, V. Ayanoor-Vitikkate, J. Beaujour, D. Bedau, D.
Berman, A. L. Bogdanov, Y. Chapuis, J. Cushen, E. E. Dobisz, G. Doerk, H.
Gao, M. Grobis, B. Gurney, W. Hanson, O. Hellwig, T. Hirano, P. Jubert, D.
Kercher, J. Lille, Z. Liu, C. M. Mate, Y. Obukhov, K. C. Patel, K. Rubin, R. Ruiz,
M. Schabes, L. Wan, D. Weller, T. Wu, and E. Yang, “Bit-patterned magnetic
recording: Theory, media fabrication, and recording performance,” IEEE Trans.
Magn. 51, 1–42 (2015).
19
I.Lemesh,K.Litzius,M.B
€
ottcher, P. Bassirian, N. Kerber, D. Heinze, J.
Z
azvorka, F. B€
uttner, L. Caretta, M. Mann, M. Weigand, S. Finizio, J. Raabe,
M.-Y. Im, H. Stoll, G. Sch€utz, B. Dup
e, M. Kl€
aui,andG.S.D.Beach,
“Current-induced skyrmion generation through morphological thermal tran-
sitions in chiral ferromagnetic heterostructures,” Adv. Mater. 30, 1805461
(2018).
20
S. Eisebitt, J. L€uning, W. F. Schlotter, M. L€
orgen, O. Hellwig, W. Eberhardt,
and J. St€
ohr, “Lensless imaging of magnetic nanostructures by X-ray spectro-
holography,” Nature 432, 885–888 (2004).
21
B. Pfau and S. Eisebitt, “X-ray holography,” Synchrotron Light Sources and
Free-Electron Lasers (Springer Cham, 2015).
22
N. Otsu, “A threshold selection method from gray-level histograms,” IEEE
Trans. Syst., Man, Cybern. 9, 62–66 (1979).
23
D. Maccariello, W. Legrand, N. Reyren, K. Garcia, K. Bouzehouane, S. Collin,
V. Cros, and A. Fert, “Electrical detection of single magnetic skyrmions in
metallic multilayers at room temperature,” Nat. Nanotechnol. 13, 233–237
(2018).
24
B. Pfau, C. M. G€
unther, E. Guehrs, T. Hauet, H. Yang, L. Vinh, X. Xu, D.
Yaney, R. Rick, S. Eisebitt, and O. Hellwig, “Origin of magnetic switching field
distribution in bit patterned media based on pre-patterned substrates,” Appl.
Phys. Lett. 99, 062502 (2011).
25
T. Thomson, G. Hu, and B. D. Terris, “Intrinsic distribution of magnetic
anisotropy in thin films probed by patterned nanostructures,” Phys. Rev. Lett.
96, 257204 (2006).
26
C. Burrowes, N. Vernier, J.-P. Adam, L. Herrera Diez, K. Garcia, I. Barisic, G.
Agnus, S. Eimer, J.-V. Kim, T. Devolder, A. Lamperti, R. Mantovan, B. Ockert,
E. E. Fullerton, and D. Ravelosona, “Low depinning fields in Ta-CoFeB-MgO
ultrathin films with perpendicular magnetic anisotropy,” Appl. Phys. Lett. 103,
182401 (2013).
27
F. B€
uttner, C. Moutafis, A. Bisig, P. Wohlh€
uter, C. M. G€
unther, J. Mohanty, J.
Geilhufe, M. Schneider, C. v Korff Schmising, S. Schaffert, B. Pfau, M.
Hantschmann, M. Riemeier, M. Emmel, S. Finizio, G. Jakob, M. Weigand, J.
Rhensius, J. H. Franken, R. Lavrijsen, H. J. M. Swagten, H. Stoll, S. Eisebitt, and
M. Kl€
aui, “Magnetic states in low-pinning high-anisotropy material nanostruc-
tures suitable for dynamic imaging,” Phys. Rev. B 87, 134422 (2013).
28
D. Pinna, F. Abreu Araujo, J.-V. Kim, V. Cros, D. Querlioz, P. Bessiere, J.
Droulez, and J. Grollier, “Skyrmion gas manipulation for probabilistic
computing,” Phys. Rev. Appl. 9, 064018 (2018).
29
T. Nozaki, Y. Jibiki, M. Goto, E. Tamura, T. Nozaki, H. Kubota, A. Fukushima,
S. Yuasa, and Y. Suzuki, “Brownian motion of skyrmion bubbles and its control
by voltage applications,” Appl. Phys. Lett. 114, 012402 (2019).
30
W. Jiang, X. Zhang, G. Yu, W. Zhang, X. Wang, M. Benjamin Jungfleisch, J. E.
Pearson, X. Cheng, O. Heinonen, K. L. Wang, Y. Zhou, A. Hoffmann, and S.
G. Te Velthuis, “Direct observation of the skyrmion Hall effect,” Nat. Phys. 13,
162–169 (2017).
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CAuthor(s) 2021
