Skyrmionsâ€”topologically protected vortex-like spin structuresâ€”have been proposed as the new information carriers in racetrack memory devices [1]. In order to realise such devices a small size, high speed of propagation, and minimal deflection angle are required. Modelling has shown that synthetic antiferromagnets (SAFs) present the ideal materials system to realise these aims [2]. However, their magnetic compensation makes observation of skyrmions difficult and indeed this was only recently achieved [3]. There is thus significantly more to understand about the behaviour of synthetic antiferromagnets and the skyrmions therein. Here we present a comprehensive magnetic force microscopy (MFM) and XMCD-PEEM study of a SAF multilayer composed of 20 magnetic layers alternating between CoB and CoFeB each coupled antiferromagnetically with a Ru spacer layer to the one above and below. PEEM results show that in the SAF phase the sample is spontaneously single-domain, and when exposed to a complicated field protocol, large defect-pinned domains can be stabilized. As shown in the hysteresis loop presented in Fig. 1 the SAF undergoes a phase transition between the compensated antiferromagnetic state and its field-polarised ferromagnetic state as a field is applied. MFM shows that in our samples this is as a result of defect-driven bubble nucleation where FM ordered regions nucleate and then expand to cover the entire film. Once the FM regions exceed a critical size they collapse into a skyrmion/stripe domain pattern and so retain a net zero magnetisation. At a narrow range of fields, e.g. as shown in Fig. 2 we observe a phase coexistence between the compensated AF state and the net-zero magnetisation FM state. As the magnetic field is increased we go on to observe isolated skyrmions at fields below saturation as expected in a FM system. These results give perspective on the ferromagnetic nature of skyrmions observed in systems at fields just below saturation and can help to inform the observation of true antiferromagnetic skyrmions.

Phase Coexistence and Transitions between Anti and Ferromagnetic States in a Synthetic Antiferromagnet

(1)National Physical Laboratory, Teddington, Middlesex, United Kingdom, (2)Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Madrid, Spain, (3)Czech Metrology Institute, Brno,
Czechia, (4)Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, (5)Instituto de Engenharia de Sistemas e Computadores (INESC-MN), Lisbon, Portugal, (6)University of Leeds,
Leeds, United Kingdom, (7)Istituto Nazionale di Ricerca Metrologica, Turin, Italy, (8)Sheffield Hallam University, Sheffield, United Kingdom 

**Abstract Body:** 

The interplay between thermal gradients and magnetic topological soliton systems represents an exciting frontier in the understanding of novel thermo-magnetic
interactions at the nanoscale [1,2]. Thermally driven non-equilibrium spin polarised charge currents and their interaction with the non-trivial topology of skyrmions is central in
understanding phenomena such as the topological Nernst effect in chiral magnetic systems within the context of spin caloritronics [3].
In this talk we will address aspects of scanning thermoelectric microscopy (SThEM), Fig 1 (a), where, we will present a novel thermal scanning probe technique that allows us to locally
investigate the thermoelectric response from the magnetic domain structure in YIG [4] to nanomagnetic topological solitons: domain-walls and skyrmions. By building up a localised
picture of the resulting spatially resolved electric field we can build an understanding of the underlying spin configuration.
We will discuss experimental and modelling results which elucidate to the local response from a pinned domain wall system in an ultra-thin magnetic layer, Fig 1(b). We demonstrate that
the domain-wall introduces an additional contribution to the total measured signal, Fig 1(c), which can only arise if we assume a Néel type domain-wall . We will also report on local
thermoelectric measurements of skyrmionic systems where we have investigated a set of device structures based on chiral magnetic multilayers, Fig 1(d). 

**Image Caption:** 

Fig. 1. (a) Schematic representation of the sThEM measurement setup used in this work showing the heated AFM probe used to apply the local thermal gradient. The electric field is probed
along the device ([endif]--> and the integrated response is mapped pixelwise. (b-c) sThEM micrographs for saturated and domain wall pinned configurations, respectively. (d) sThEM
micrograph of a skyrmion nucleated in a chiral magnetic multilayer. 

**References:** 

[1] Jakub Zázvorka, et al, Thermal skyrmion diffusion used in a reshuffler device Nature Nanotechnology, 14, 658–661 (2019). 
[2] Zidong Wang et al, Thermal generation, manipulation and thermoelectric detection of skyrmions, Nature Electronics, 3, 672–679 (2020). 
[3] Alexander Fernández Scarioni, Craig Barton, et al , Thermoelectric Signature of Individual Skyrmions, Phys. Rev. Lett. 126, 077202, (2021). 
[4] Alessandro Sola, Craig Barton, et al, Phys. Rev. Applied 14, 034056, (2020). 

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Scanning thermoelectric microscopy: applied to topological soliton systems

Synthetic antiferromagnets (SAFs) are of interest in a wide variety of spintronic applications owing to their net zero magnetisation and inherent tunability arising from control over complex stacking sequences [1]. They show very fast domain wall (DW) motion in response to spin torques [2].
Here we describe measurements of the current-driven DW motion in each of the separate magnetic sublattices of a SAF with structure Ta/[Ru/Pt/CoB/Ru/Pt/CoFeB]×5/Ru/Pt which displays both perpendicular magnetic anisotropy (PMA) and the Dzyaloshinskii-Moriya interaction (DMI). The thickness of the Ru layers is tuned to provide AF coupling between each pair of layers. The thicknesses of the alternating CoB and CoFeB layers are tuned to give net zero magnetisation (as measured by SQUID magnetometry) at a wide range of fields up to ~50 mT.
The magnetic films were grown on Si3N4 membranes and imaged with scanning transmission x-ray microscopy (STXM). They were patterned into 2 µm wide wires with Cu leads attached to each end. The distinct chemical composition of the two sublattices means that we could use the element specificity of STXM to observe the CoFeB separately by imaging at the Fe L3 edge, whilst contrast at the Co L3 edge is dominated by the other sublattice of CoB layers. Inverted domain structures observed at these two edges with XMCD-STXM are shown in Fig. 1, confirm the SAF ordering of the layers. Current pulses drive domain wall motion, as shown in Fig. 2, with average velocities up to ~ 40 m/s achieved at current densities as low as 3 × 1011 A/m2. These results demonstrate a low depinning current and fast motion compared to comparable FM multilayers we have previously studied, suggesting that domain walls in SAF heterostructures are superior to their ferromagnetic equivalents for low energy consumption racetrack technologies. 
**References** [1] R. A. Duine et al., Nature Phys. 14, 217 (2018)
[2] S.-H. Yang et al., Nature Nanotech. 10, 221 (2015) 

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Current Driven Domain Wall Motion in a Synthetic Antiferromagnet Multilayer

Skyrmions are of great interest in spintronic devices because their small size and the high-speed motion when driven by a current or a spin-wave (SW). Skyrmion motion
along a narrow track is important for racetrack-type spintronic devices, since a skyrmion moving along the propagation direction of an injected electrical or SW current (forward) is the
means by which data are moving[1]. To design the devices, knowing how to adjust the skyrmion motion becomes important.
We carried out simulations of SW driven skyrmion motion using OOMMF [2], with fixed parameters D = 1.5 mJ/m2, MS = 1004 kA/m, A = 3.6 pJ/m, and Ku = 1 MJ/m3. We found that for tracks narrower than 50 nm the skyrmion always moves forwards. For wider tracks, the skyrmion will initially move both backward and close to the track edge, before moving forward at longer times once the track edge is reached, as shown in Fig 1. We attribute this to an additional repulsive force on the skyrmion from the track edge. For samples with Gilbert damping
constant α > 0.06, the skyrmion will move forward without retrograde motion.
The Thiele equation is a widely-used way to analyse skyrmion motion. The SW driving force on a skyrmion is usually the SW scattering force [3], but the strength of the scattering and the
energy change associated with changes in skyrmion size owing to absorbed SWs are hard to extract from magnetization data. Thus, we use the SW transmission T and reflection
coefficients R to make an estimate of the forces involved. We can obtain T from the ratio of the SW amplitude downstream of the skyrmion and without skyrmion at same position.
Similarly, we obtain R from the difference between magnetization data upstream of the skyrmion and without skyrmion.
As an example, we consider the data from a simulation with track width w = 100 nm and α = 0.03. By Analysing T and R, the decrease in T after ~30 ns, shown in Fig.2, will reduce the
effort that leads to the skyrmion moving backward. Meanwhile the increasing force from the sample edge also helps the skyrmion overcome the Spin-Ttansfer Torque between transmitted
SW and skyrmion[4], allowing it to move forwards. 
**References** 
1. Sampaio, J., Cros, V. et al. Nature Nanotech 8, 839–844 (2013) 
2. Donahue, M., Porter D. et al, National Institute of Standards and Technology(1999) 
3. Zhang, X. et al New J. Phys. 19, 065001 (2017) 
4. Yan, X., S. Wang et al. Phys. Rev. Lett. 107, 177207 (2011) 

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The snapshots of w = 40 nm, 90 nm tracks 

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Time-dependent SW T, R, A and skyrmion acceleration data

Transient retrograde motion of spin wave driven skyrmions in multilayer wave guides

It has been predicted and measured that topologically non-trivial magnetisations can provide an extra contribution to the Hall resistivity (Rxy), called the topological Hall effect (THE)1. Skyrmions have a topology defined by the winding number, S, which takes an integer value dependent upon the number of total ‘twists’ in their magnetisation. The THE has been shown to be present in many B20 materials with bulk Dzyaloshinkii-Moriya Interaction (DMI) hosting skyrmions but the picture is less clear for multilayers with interfacial DMI. Observations by Maccariello et al. saw resistivity effects that could be accounted for by only the ordinary and anomalous Hall effects (OHE & AHE)2. In contrast, work by Zeissler et al. saw an extra contribution beyond the OHE and AHE that was larger than the THE predicted by theory3. In this work, Hall transport measurements combined with imaging of the magnetic texture were used to identify such contributions to understand discrepancies between the predicted1, and observed2,3, magnitudes of the topological contribution. Measurements of Rxy(B) were performed in [Pt|CoB|Ir]xN multilayers with different repeat numbers, N, over a range of temperatures from 290 K to 2 K. Figure 1 shows the temperature dependence of the anomalous Hall resistivity at saturation, ρA, with an increase in size at T &lt; 20 K, for a sample with N=4. The Rxy measurements for the same sample were analysed in combination with SQUIDVSM magnetometry data to produce Figure 2. The maximum excess Hall resistivity, ρexcess, is observed to increase with temperature and cannot be accounted for by the ordinary and anomalous Hall effects alone. This implies an extra Hall effect that may be topological in nature suggesting that the maximum density of topological magnetisation textures increases with temperature.

![](https://assets.underline.io/uploads/markdown_image/1/image/1a86da2275fb423bada15ee48b4609a9.jpg)

Fig. 1 Anomalous Hall resistivity at saturation, ρA, vs T showing an increase in size for T < 20 K, in samples of Ta|Pt|[CoB|Ir|Pt]x4 Pt multilayers.

![](https://assets.underline.io/uploads/markdown_image/1/image/d834fd8cf6941127ea0fd52e6ae23c9a.jpg)

Fig. 2 Excess Hall resistivity (possibly topological in nature) that cannot be accounted for by ordinary or anomalous Hall effects, ρexcess, vs T, showing an increase in the height of the maximum peak as temperature increases.

Observation of Increasing Topological Hall Resistivity with Temperature in Skyrmion Hosting Magnetic Multilayers with [Pt|CoB|Ir]xN Structure

Skyrmions have clear advantages for future spintronic devices over domain walls in terms of information carrying and storage, however there are still many open questions left and inherent challenges in the transition to applications. Here we study the effect of an additional interfacial spin-transfer torque (ISTT) [1], as well as the well-established spin-orbit torque (SOT), on skyrmion collections [2] – group of skyrmions dense enough that they are not isolated from one another – in magnetic multilayers, by comparing modelling using Boris [3], with experimental results. We show that skyrmion collective motion has additional effects not reproduced when compared to modelled isolated skyrmions [1]. In particular, as the skyrmion collection density increases the effect of local disorder is reduced, leading to reduced threshold current densities, and a sharper dependence of skyrmion Hall Angle (SkHA) on velocity in the depinning regime, in agreement with experimental results. When including both the ISTT and SOT, the small SkHA observed in experiment are in good agreement, also explaining the observed diameter-independent SkHA [4], as seen in Figure 1. Contrary to the model which considers the SOT as the only driving torque, and which predicts a monotonically increasing SkHA with decreasing diameter, inclusion of ISTT results in SkHA closely aligned to experimental results, particularly when the effect of local disorder and skyrmion-skyrmion interactions are taken into account. Our results shed further light on collective current-driven skyrmion motion in magnetic multilayers and highlight the significance of the ISTT in understanding current-driven skyrmion motion in magnetic multilayers.

![](https://assets.underline.io/uploads/markdown_image/1/image/219d9cf02b4f240924efc702e30f317a.jpg)

Figure 1. Collective SkHA dependence on skyrmion diameter for (a) N = 50 Sk/µm2 and (b) N = 100 Sk/µm2. (c) Experimentally obtained SkHA from skyrmion collections with a range of diameters with an average current density of 2×1011 A/m2. The overlaid dashed and solid lines show the ideal isolated skyrmion case – independent of current density – for the SOT and ISTT+SOT, respectively. The solid blue line in panel (b) represents a Savitzky-Golay fit to the simulated skyrmion motion, for a current density of Jc = 2×1011 A/m2.

Collective Skyrmion Motion Under the Influence of an Additional Interfacial Spin-Transfer Torque

Synthetic antiferromagnets (SAFs) are of interest in a wide variety of spintronic applications owing to their net zero magnetisation and inherent tunability arising from control over complex stacking sequences [1]. They show very fast domain wall (DW) motion in response to spin torques [2]. Here we describe current-driven DW motion in an SAF with stack structure Ta/[Ru/Pt/CoB/Ru/Pt/CoFeB]×5/Ru/Pt which displays both perpendicular magnetic anisotropy (PMA) and the Dzyaloshinskii-Moriya interaction (DMI). The alternating CoB and CoFeB layers had their thicknesses adjusted to give net zero magnetisation (as determined by SQUID-VSM) for applied fields up to ~500 Oe. They were patterned into 2 µm wide wires with Cu leads attached to each end. These were fabricated on Si3N4 membranes to permit imaging of DW motion using scanning x-ray transmission microscopy. The distinct chemical composition of the two sublattices means that we could use the element specificity of this technique to observe the CoFeB separately whilst imaging at the Fe L3 edge, whilst contrast at the Co L3 edge is dominated by the other sublattice. Inverted domain structures observed at these two edges, as shown in Fig. 1, confirm the SAF ordering of the layers. Current pulses drive domain wall motion, as shown in Fig. 2, with velocities up to ~ 20 m/s achieved at current densities as low as 4 × 1011 A/m2.

![](https://assets.underline.io/uploads/markdown_image/1/image/d87de30dbef334ff75e4447e90cf2feb.jpg)

Fig. 1: STXM images acquired at zero field the Co and Fe L3 edges, which probe different sublattices of the SAF. A finger-shaped Cu lead is visible on the left. 1 µm scale bar.

![](https://assets.underline.io/uploads/markdown_image/1/image/04b915124bc7866fb80c310fb03a761b.jpg)

Fig. 2: DW velocity against current density measured using 5 ns current pulses.

Current-Driven Domain Wall Motion in a Synthetic Antiferromagnet Multilayer

The presence of a Dzyaloshinskii-Moriya interaction (DMI) in perpendicularly magnetised thin films stabilises Néel type domain walls of fixed chirality, as opposed to the Bloch walls that are formed in the absence of a DMI [1]. Néel walls of fixed chirality have been shown to be driven efficiently in the same direction by electric currents through spin-orbit torques [2,3]. Later, a large tuning of the DMI with an applied voltage was demonstrated [4], which can be used e.g. for electric field control of magnetic domain wall motion via the modulation of the DMI [5]. Here, we demonstrate an alternative mechanism for the control of domain wall type: using micromagnetic simulations and analytical modelling, we show that the presence of a uniaxial in-plane magnetic anisotropy can also lead to the formation of Néel walls in the absence of a DMI. It is possible to abruptly switch between Bloch and Néel walls via a small modulation of both the in-plane, but also the perpendicular magnetic anisotropy [6]. This opens up a route towards efficient electric field control of the domain wall type with tiny applied voltages, as the magnetic anisotropy can be modulated via the direct voltage controlled magnetic anisotropy (VCMA) mechanism [7], or via magnetoelastic anisotropy induced through coupling to a piezoelectric element [8].

![](https://assets.underline.io/uploads/markdown_image/1/image/7bef5f5df8869fd862ccaab94b5a3626.jpg)

Fig. 1 In a perpendicularly magnetised thin film, domain walls (DWs) are generally of Bloch type (bottom left). The presence of a DMI (top left), stabilises Néel walls. Alternatively, and in-plane magnetic anisotropy can also form Néel walls (bottom right). An increase in the perpendicular magnetic anisotropy switches the DW type back to Bloch (top right).

Switching between Magnetic Bloch and Néel Domain Walls with Anisotropy Modulations

In this last decade, experimental results and their understanding have led to magnetic skyrmions becoming promising candidates for the storage and processing of digital information [1]. However, some key barriers such as reducing their size, enhancing their stability at room temperature, or their low-power manipulation under electrical current have not yet been overcome, meaning that they are rarely integrated in actual devices [2]. To surmount these limitations, it has been proposed to study these magnetic textures in antiferromagnets or synthetic antiferromagnets (SAFs) instead of the conventional ferromagnetic layers that are usually considered [3,4]. In this more complex system, multiple ferromagnetic layers are coupled antiferromagnetically through a non-magnetic spacer layer via the RKKY interaction (Fig a) [4,5]. By switching to these systems, two crucial points need to be addressed. First, a drastic reduction of stray fields is expected in SAFs due to the anti-alignment of magnetization, which should reduce the size of the skyrmions [6]. Second, it is not possible to manipulate a conventional skyrmion in the driving force direction in a ferromagnet due to its topology that intrinsically induces a deflection known as the skyrmion Hall effect [7]. In SAF systems, since the magnetisation of the skyrmions in each magnetic layer are opposite, it is expected that the two deflections cancel each other out and the two skyrmions move in the current direction [3]. Even if skyrmions have recently been observed in SAFs [4,8,9], a clear and simple micromagnetic description of both the static and dynamic properties of such skyrmions is so far lacking to further understand this phenomenon. In order to improve the description of these properties and highlight the expected benefits of using SAFs rather than conventional ferromagnets, we simulate numerically the behavior of skyrmions in bilayer SAFs for a large range of parameters. We also adapt the ferromagnetic analytical formalism [10] to SAF systems. This leads to results that are in good agreement with the numerical simulations whilst also highlighting the underlying mechanisms. First, we investigate the stability region of SAF skyrmions and how their radii r evolve with micromagnetic parameters. We show that they are only slightly smaller than for ferromagnetic systems (Fig b), but that they exist for a larger range of parameters. Second, we study the dynamics of these skyrmions under spin currents. We find, as expected, that SAF skyrmions move at a faster velocity v than in a conventional ferromagnet (Fig c) for a given current density J, and move in the applied current direction (Fig d) with zero skyrmion Hall angle θSky. By using the analytical model based on the Thiele equation, we are able to recover these dynamics (Fig c and d) and identify the required condition for the vanishing of the topological deflection. Finally, we unbalanced the SAF by asymmetrizing the skyrmions in each layer in different ways in order to verify the condition for vanishing deflection. The results obtained highlight the qualitative benefits of SAF skyrmions and propose some methods for more quantitative optimizations.

**References:**

[1] The 2020 skyrmionics roadmap: C. Back et al., J. Phys. D: Appl. Phys. 53 (2020) [2] Magnetic skyrmions: advances in physics and potential applications: A. Fert, et al. Nat. Rev. Mat. 2, 17031 (2017) [3] Static and dynamical properties of antiferromagnetic skyrmions in the presence of applied current and temperature: J. Barker, et al. Phys. Rev. Lett. 116, 147203 (2016) [4] Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets. W. Legrand et al., Nat. Mat. 19, 34–42 (2020) [5] Oscillatory magnetic exchange coupling through thin copper layers: S. S. P. Parkin, et. al . Phys. Rev. Lett. 66, 2152–2155 (1991) [6] Theory of isolated magnetic skyrmions: from fundamentals to room temperature applications: F.Büttner, et al,. Sci. Rep. 8 4464 (2018) [7] Nucleation, stability and current-induced motion of isolated magnetic skyrmions in nanostructures: J. Sampaio, Nat. Nano. 8, 839-844 (2013) [8] Imaging non-collinear antiferromagnetic textures via single spin relaxometry: A. Finco et al., arXiv:2006.13130v1 (2020) [9] Exploring different facets of magnetic skyrmion nucleation and dynamics in ultra-thin films: R. Juge, PhD Thesis, Université Grenoble-Alpes (2020) [10] The skyrmion-bubble transition in a ferromagnetic thin film: A. Bernand-Mantel et.al. SciPost Phys. 4, 027 (2018)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/060a538fb9d9988c2db214e60cb7057e.jpg)
(a) Sketch of the skyrmion structure and motion under current in ferromagnetic and SAF systems. Radii (b), velocity (c) and deflection (d) for a ferromagnetic skyrmion (in blue) and a SAF skyrmion (in red) with the same micromagnetic parameters versus the current density J. Points correspond to the micromagnetic numerical simulations and lines to the analytical model.

 Statics and Dynamics of Skyrmions in Synthetic Antiferromagnets : Benefits and Micromagnetic Understanding

The presence of a Dzyaloshinskii-Moriya interaction (DMI) in perpendicular magnetized thin films stabilizes Néel type domain walls of fixed chirality, as opposed to the Bloch walls that are formed in the absence of a DMI [1]. Néel walls of fixed chirality have been shown to be driven efficiently in the same direction by electric currents through spin-orbit torques [2,3]. Later, a large tuning of the DMI with an applied voltage was demonstrated [4], which can be used for example for electric field control of magnetic domain wall motion via the modulation of the DMI [5]. Here, we demonstrate an alternative mechanism for the control of domain wall type: Using micromagnetic simulations and analytical modeling, we show that the presence of a uniaxial in-plane magnetic anisotropy can also lead to the formation of Néel walls in the absence of a DMI. It is possible to abruptly switch between Bloch and Néel walls via a small modulation of both the in-plane, but also the perpendicular magnetic anisotropy [6]. This opens up a route towards efficient electric field control of the domain wall type with tiny applied voltages, as the magnetic anisotropy can be modulated via the direct voltage controlled magnetic anisotropy (VCMA) mechanism [7], or via magnetoelastic anisotropy induced through coupling to a piezoelectric element [8].

**References:**

1. A. Thiaville, S. Rohart, E. Jué, V. Cros, and A. Fert, EPL (Europhysics Letters) 100, 57002 (2012). 2. K.-S. Ryu, L. Thomas, S.-H. Yang, and S. S. P. Parkin, Nat. Nanotech. 8, 527–533 (2013) 3. S. Emori, U. Bauer, S.-M. Ahn, E. Martinez, and G. S. D. Beach, Nat. Mater., 12, 611–616 (2013) 4. T. Srivastava, et al., Nano Letters 18, 4871 (2018) 5. T. Koyama, Y. Nakatani, J. Ieda, and D. Chiba, Science Advances 4 (2018) 6. K. J. A. Franke, et al., in preparation (2021) 7. T. Maruyama, et al., Nat. Nanotech. 4, 158 (2009). 8. S.Li, et al., J, Appl. Phys. 117, 17D702 (2015)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5815f993e947e36c366298e73960792b.jpg)
In a perpendiular magnetized thin film, domain walls (DWs) are generally of Bloch type (bottom left). The presence of a DMI (top left), stabilises Néel walls. Alternatively, and in-plane magnetic anisotropy can also form Néel walls (bottom right). An increase in the perpendicular magnetic anisotropy switches the DW type back to Bloch (top right).

 Control of Magnetic Domain Wall Type using Anisotropy Modulations

Magnetic skyrmions are topologically-nontrivial spin textures with particle-like properties [1]. Their size, topological stability, and mobility suggest their use in future generations of spintronic devices, the prototype of which is the skyrmion racetrack [2]. To realise a racetrack requires three basic operations: the nucleation (writing), propagation (manipulation), and detection (reading) of a skyrmion, all by electrical means. Here we show that all three are experimental feasible at room temperature in Pt/Co/Ir or Pt/CoB/Ir multilayers in which the different heavy metals above and below the magnetic layer break inversion symmetry and induce chirality by means of the Dzyaloshinskii-Moriya interaction, defining the structure of Néel skyrmion spin textures [3]. We show deterministic nucleation on nanosecond timescales using an electrical point contact on top of the multilayer [4] (Figure 1), current-driven propagation along a wire in which the skyrmions are channelled by defects in the multilayer [5], and their detection by means of the Hall effect (Figure 2) that reveals an unexpectedly large contribution to the Hall signal that correlates with the topological winding number [6].

**References:**

[1] N. Nagaosa & Y. Tokura, Nat. Nanotech. 8, 899 (2013). [2] A. Fert et al. Nature Nanotech. 8, 152 (2013). [3] K. Zeissler et al. Sci. Rep. 7, 15125 (2017). [4] S. Finizio et al., Nano Lett. 19, 7246 (2019). [5] K. Zeissler et al., Nature Comm. 11, 428 (2020) [6] K. Zeissler et al. Nature Nanotech. 13, 1161 (2018).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e2d829c356fc36105eeb0bb2e9c2db72.jpg)
Figure 1. STXM images (a) before and (b) after electrical nucleation of a skyrmion at a 500 nm wide injector contact to a Pt/CoB/Ir multilayer.

![](https://assets.underline.io/uploads/markdown_image/1/image/031a069098aadac7fb343bb1f3bd715d.jpg)
Figure 2. STXM image of two skyrmions in an electrically-connected 1 µm diameter Pt/Co/Ir multilayer dot. 500 nm scale bar.

 Skyrmions in chiral magnetic multilayers

One of the tools to move a skyrmion is an injected current[1,2], which gives rise to the risk of producing excessive heat. On the other hand, spin-waves (SW) are a promising way to drive skyrmions without producing such high temperatures and hence affecting the skyrmionic device's performance. Most recent work on SW-driven skyrmion motion is based on micromagnetic simulations on single-layers with either small magnetic track width (W), high SW excitation rf field (Arf), or low Gilbert damping constant α[3,4]. However, to complement the realization of skyrmion motion experimentally, simulations should meet experimentally achievable conditions at the same time: W ≥100nm, Arf ≤100mT and α &gt;0.05. The dataset and characteristic analysis we present concern SW driven skyrmion simulations by OOMMF[5] with fixed parameters, D=1.5 mJ/m2, MS=1004 KA/m, A=3.6 pJ/m, Ku=1 MJ/m3. We varied the α=0.02-0.06, W=40-100 nm and Arf=100-800 mT. The size of the relaxed skyrmion is from 20nm to 23nm when W increases from 40nm to 100nm, so there is more than 5 nm between the skyrmion to each sample edge at initial stage. Fig.1 shows the skyrmion displacement (dsky) with time along the SW propagation direction for various W is shown. When W &gt;50 nm, the skyrmion will initially move opposite to the SW propagation direction before moving forward at longer times. Fig.2 shows that with larger α, the skyrmion will have smaller initial velocity when moving backward. If the leading edge of the skyrmion is regarded as a planar wall on the sample, the domain wall (DW) plane is predicted to rotate when linear momentum transfer between the SW and DW occurs. The angle between the DW wall plane and the out-of-sample direction is defined as DW wall plane angle (ΦDW)[6]. Also, the inset shows that ΦDW of skyrmion leading edge has similar behaviour to the dsky, but with an offset. The skyrmion backward motion gives a possible observation result in the future and guidance about finding a balance between W and magnetic properties to have skyrmions with aiming motion type.

![](https://assets.underline.io/uploads/markdown_image/1/image/20d3a9acd993b9c5372ac498eb39b2f1.jpg)

Fig.1 Time-dependent skyrmion displacement in nm for various W.

![](https://assets.underline.io/uploads/markdown_image/1/image/3a0f9f542c8a882ca49dfb2dc79008fd.jpg)

Fig.2 Skyrmion displacement with time for various α. Inset: comparison between ΦDW and skyrmion displacement when α=0.06.

Transient retrograde motion of spin wave-driven skyrmions in multilayer wave guides

ROB: Recent Advances In Magnetic Imaging

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Please register for the MMM 2022 conference to join the event.

MMM 2022

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

ROA: Magnetic Characterization from Nano to Macro

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Chair:** Takeshi Seki, *Tohoku University*

EPA: Antiferromagnetic Spintronics III

poster

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Co-Chairs:** Joseph Sklenar, *Wayne State University* and Shuyuan Shi, *Beihang University*

GPA: Magnetization Dynamics VI

**Session chair:** Max Hirschberger, The University of Tokyo



GOF - Skyrmions, Antiskyrmions and Topology

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

**Session chair:** Olivier Boulle, SPINTEC


HOE - Magnetic Skyrmions

**Session chair:** Jean-Yves Chauleau, CEA-SPEC


HOF - Dynamics in AF-coupled Materials

**Session chair:** Valentine Novosad, Argonne National Laboratory


HOH - Magnetization Dynamics in Soft Materials

*Session Co-Chair: Daria Gusakova, SPINtronique et Technologie des Composants*

*Session Co-Chair: Joo-Von Kim, Université Paris-Saclay*

These on-demand presentations are available to view at your leisure. 

AE: Micromagnetic Modelling

INTERMAG 2021 Welcome Video



	
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Want to buy a ticket? 

Register for INTERMAG 2021 here

[![](https://assets.underline.io/uploads/markdown_image/1/image/17ce76e7960db633258024eef8d6da7f.png)](https://intermag.org/register)

Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

*Session Chair: Dennis Meier, Norges teknisk-naturvitenskapelige universitet*

These on-demand presentations are available to view at your leisure. 

FE: Electric Field Effects and Magnetization Switching

*Session Chair: Riccardo Tomasello, Foundation for Research and Technology - Hellas*

These on-demand presentations are available to view at your leisure.

HA: New Trends in Skyrmionics: Materials, Dynamics and Detection Techniques

**Session chairs:** Liliana Buda-Prejbeanu, SPINtronique et Technologie des Composants and Yoshinobu Nakatani, The University of Electro-Communications



Christopher Marrows

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Presentations