B2-ordered FeRh undergoes a thermally activated first-order phase transition between antiferromagnetic (AF) and ferromagnetic (FM) order upon heating, with a transition temperature between 350 - 380 K [1], making it an ideal candidate for use in a wide range of magnetic storage architectures [2]. The evolution of magnetic domains through the transition has been well-characterized [1-5]. However, behaviours such as the domain nucleation mechanism and subsequent evolution of the magnetic domains along the sample thickness through the phase transition remain unclear [1,3-5]. Here, we present three-dimensional (3D) reconstructions of the magnetic structure through the sample volume at various temperatures through the phase transition, achieved using magnetic laminography [6-7]. Imaging cross-sections through the sample thickness reveal that domains for both types of magnetic order nucleate at the surface and travel into the bulk of the sample with changing temperature. Creating a complex 3D magnetic structure, in which the evolution of the magnetic state along the sample thickness with temperature is non-uniform. We also observe quasi-uniform FM domains at 310 K when heating, in contrast to the expected flux-closed state [1], as well as AF regions where FM domain walls are expected. Both observations can be attributed to the exchange coupling between adjacent AF and FM regions, which plays a key role determining the FM configuration in this material. 

**References:** 

[1] T. P. Almeida et al., Phys. Rev. Materials 4, 034410 (2020). 
[2] R. C. Temple et al., Phys. Rev. Materials 2, 104406 (2018). 
[3] C. Gatel et al., Nat. Comms. 8, 15703 (2017). 
[4] V. Uhlir et al., Nat. Comms. 7, 13113 (2016). 
[5] M. A. de Vries et al., Appl. Phys. Lett. 104, 232407 (2014). 
[6] C. Donnelly et al., Nature Nanotech. 15, 356 (2020) 
[7] K. Witte et al., Nano Lett. 20, 1305 (2020). 

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Three Dimensional Nucleation Kinetics Through the First

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

The spin Hall effect, and its inverse, are important spin-charge conversion mechanisms widely investigated due to their fundamental importance in the development of spintronics devices. Its measurement has been mostly related to electrical detection schemes involving an interface with another magnetic material and thus, a combination of the properties of both materials as well as the interface are measured. The large scattering of reported results from these methods for the same material and temperature call out for a more direct and interface-free approach. Optical detection schemes have been successfully used for the determination of SHE in semiconductor. However, this approach has proven challenging for metallic systems, due to their considerably shorter spin diffusion lengths. Only recently, optical measurements for Pt and W have been reported [1]. Considering that magnetic circular dichroism (XMCD) has become a reference tool for precision measurements of small or diluted magnetic signals, We propose the use of XMCD-PEEM microscopy for direct, interface-free determination of SHE in metals. In particular, we report the observation of spin separation due to SHE in a single layer of Bi-doped Cu (Cu95Bi5), a material in which giant SHE has been already reported [2,3]. We have performed interface free x-ray spectroscopy measurements at the Cu L3,2 absorption edges while applying electrical current to the sample. The sign of spin accumulation depends on the direction of the current and the amplitude of the X-ray magnetic circular dichroism (XMCD) signal scales with the density current and have different sign when measuring in the L2 or L3 absorption edges, as expected for SHE. We have measured an induced magnetic moment of (2.7 ± 0.5) x 10-12μB A-1 cm2 per Cu atom averaged over the probing depth, which is of the same order as for Pt measured by magneto-optics. Our results constitute the proof of concept for the direct, interface free and element-selective measurement of the SHE in a single material by means of X-ray spectromicroscopy and highlight the potential of CuBi for spin-charge conversion applications [4].

![](https://assets.underline.io/uploads/markdown_image/1/image/0f5bce09fb325fa1a3fcfbf281b8cd98.jpg)

(a) Visualization of the spin accumulation in a Cu95Bi5 electrode. (b) XMCD signal.

Direct X-ray detection of the spin Hall effect in CuBi

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

Three dimensional magnetic systems promise significant opportunities for applications, for example providing higher density devices and new functionality associated with complex topology and greater degrees of freedom [1,2]. For the experimental realisation of these new properties, appropriate characterisation techniques are required to determine both the three-dimensional magnetic structure, and its response to external stimuli. In this talk, I will describe our recent progress in the development of new capabilities for the imaging of three-dimensional magnetic systems, and their dynamic behaviour. For three-dimensional magnetic imaging, we have developed X-ray magnetic nanotomography [3]. By measuring high resolution 2D XMCD projections [4] of the sample for many angles about a dual rotation axis experimental setup, and combing these with a new iterative reconstruction algorithm [5], we determine the complex three-dimensional magnetic patterns within the bulk of a micrometre-sized soft magnetic pillar with 100 nm spatial resolution, as shown in Figure 1. The internal magnetic configuration reveals a complex network of topological magnetic features such as vortices, antivortices and domain walls and, at the crossing points of these structures, we observe the presence of Bloch point singularities [3]. The identification, and interpretation, of nanoscale topological objects within the complex reconstructed magnetic configurations – that consist of millions of pixels – represents a significant challenge. To address this, we have recently implemented calculations of the magnetic vorticity [6,7], a vector that represents the flux of the skyrmion number density, and thus encodes the topology of the magnetic configuration. In this way, not only can we locate and identify the presence of topological structures (Figure 1e,f), but we gain new insights into 3D magnetic solitons, leading to the first observation of magnetic vortex rings [7], as shown in Figure 1g. Lastly, in addition to the static magnetic configuration, the dynamic response of the 3D magnetic configuration to excitations is key to our understanding of both fundamental physics, and applications. With our recent development of X-ray magnetic laminography [8,9] (Figure 2), it is now possible to determine the magnetisation dynamics of a three-dimensional magnetic system [8]. In this way, we have been able to map the dynamics of a magnetic microdisc in response to the excitation of a 500 MHz magnetic field, revealing the motion of vortex domain walls within the bulk of the structure, as well as mapping the coherent rotation modes of the magnetisation in three dimensions (Figure 2c,d), with spatial and temporal resolutions of 50 nm and 70 ps, respectively. These new experimental capabilities of X-ray magnetic imaging open the door to the elucidation of complex three-dimensional magnetic structures, and their dynamic behaviour.

**References:**

[1] A. Fernández-Pacheco, et al., “Three-dimensional nanomagnetism” Nat. Comm. 8, 15756 (2017) [2] C. Donnelly & V. Scagnoli, “Imaging three-dimensional magnetic systems with X-rays” J. Phys. D: Cond. Matt. (2019). [3] C. Donnelly et al., “Three-dimensional magnetization structures revealed with X-ray vector nanotomography” Nature 547, 328 (2017). [4] C. Donnelly et al., “High-resolution hard x-ray magnetic imaging with dichroic ptychography” PRB 94, 064421 (2016). [5] C. Donnelly et al., “Tomographic reconstruction of a three-dimensional magnetization vector field” NJP 20, 083009 (2018). [6] N. R. Cooper, “Propagating magnetic vortex rings in ferromagnets.” PRL. 82, 1554 (1999). [7] C. Donnelly et al., “Experimental observation of vortex rings in a bulk magnet” Nat. Phys. (2020) [8] C. Donnelly et al., “Time-resolved imaging of three-dimensional nanoscale magnetization dynamics”, Nat. Nano. 15, 356 (2020). [9] K. Witte et al., “From 2D STXM to 3D Imaging: Soft X-ray Laminography of Thin Specimens”, Nano Lett. 20, 1305 (2020).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/0e2d9057483d2b7b45d4d6c5b16ede99.jpg)
Figure 1. X-ray magnetic tomography of a GdCo micropillar (a) reveals a complex internal magnetic configuration. A horizontal slice (b) contains a number of vortices (c) and antivortices (d). Through calculations of the magnetic vorticity vector, we can identify the presence of topological structures (e) and magnetisation singularities (f) within the bulk of the micropillar. By plotting the magnetic vorticity, we identify magnetic vortex rings of circulating vorticity (g). a-d are reproduced from [3], and e-g are reproduced from [8].

![](https://assets.underline.io/uploads/markdown_image/1/image/72ea02148e85a8623efddf043a46be9a.jpg)
Figure 2 Pump-probe X-ray magnetic laminography (a) allows for the mapping of the magnetization dynamics of a magnetic microdisc (b) with spatial and temporal resolutions on the order of nanometers and picoseonds, respectively. Coherent rotation modes of the magnetization are shown for a cross section (c) and a lower slice of the structure containing vortex domain walls (d). a-d reproduced from [8].

Imaging 3D magnetic configurations with X-rays

Understanding magnetization dynamics in nanosized systems is a key condition not only to realize innovative new applications, but also to further expand our comprehension of the underlying fundamental physics. Only recently has it been possible to image magnetic objects such as domain walls (DWs) with high temporal and spatial resolution and versatile environments or excitations, using, for example time resolved x-ray magnetic circular dichroism with scanning transmission x-ray microscopy (XMCD STXM). Continuous developments of this technique have allowed for a shift of interest from simple systems such as flat nanostrips, that lend themselves more readily to magnetic imaging, to more intricate systems such as three dimensional nanostructures, with added complexity from the volume [1,2]. A textbook case for such an investigation is provided by cylindrical magnetic nanowires (NWs) featuring a novel type of DW, the Bloch-point wall (BPW) [3] which exhibits azimuthal curling of magnetic moments around a Bloch-point on the NW axis. The dynamics of these walls stand out compared to DWs in flat nanostrips due to fascinating theoretical predictions of fast, stable speeds and the controlled emission of spin waves [4]. Recent experiments in NWs indicate that the Œrsted field induced by nanosecond pulses of current plays a key role in stabilising walls exclusively of the BPW type and further switches the azimuthal circulation to be parallel to the field [5]. This allows controlling the wall structure and enables fast DW motion with speeds &gt; 600 m/s and an absence of Walker breakdown. The importance of the Œrsted field in NWs was further studied with simulations to determine a strong radial dependence, scaling as one-over radius cubed, and a complex mechanism of the BPW switching process, involving nucleation and annihilation of pairs of Bloch-points [6]. In the case of longitudinally magnetised domains, the peripheral magnetic moments also tend to align with the Œrsted field with the degree of tilt related to a competition between magnetic exchange and Zeeman energy. It is clear that the Œrsted field has a major influence on magnetization dynamics in NWs, yet few predictions have been confirmed experimentally due to the complexity of such experiments. Further, without time resolved measurements, no quantitative comparisons of eg. tilt angles in magnetization may be made with the simulations. Verifications of these effects are therefore strongly required in order to control the system and employ it in possible future applications. Here, we make use of time resolved XMCD STXM to image the magnetization dynamics in NWs subjected to nanosecond pulses of electrical current. Time resolved images were acquired with a temporal resolution of 200 ps, to image the effect of positive and negative polarity 3 ns duration voltage pulses of chosen amplitude applied to magnetically soft Co30Ni70 NWs with diameters 93, 97 and 101 nm. We first observed the tilting of magnetization towards the applied Œrsted field direction in longitudinally magnetized domains (Fig. 1a) and created a model based on the absorptivity of x-rays and a description of the magnetization in a NW cross section to accurately reproduce the observed magnetic contrast and extract quantitative information. We find that the degree of tilt on the surface of these NW samples is of the order of 18±8° per 1012 A/m2 applied (Fig. 1b), which is in agreement with theoretical predictions from ref. [6]. We then observe the expansion (Fig. 2b,d) and compression (Fig. 2a,c) of the BPW width due to the application of a parallel and antiparallel Œrsted field, respectively. This effect, previously predicted by simulations, occurs when the applied current density is insufficiently strong to induce the BPW circulation switching. The magnetic contrast of the phenomenon is again reproduced with our simple model giving quantitative information about this “breathing” of the BPW. We expect that this work lays the foundation for and provides an incentive to further studying complex magnetisation dynamics in NWs. With increased control of the NW materials, the predicted ultrafast DW motion and associated spin wave emissions [4] may be visualized using this technique. Further, the quantitative analysis provided herein shows the depth of information obtainable with time resolved XMCD STXM and that a direct comparison of the observed dynamics to ie. simulations and theory is possible. This type of direct collaboration will significantly grow the understanding of three dimensional magnetic nanosized systems and enable better control over them.

**References:**

[1] C. Donnelly et al., Time-resolved imaging of three-dimensional nanoscale magnetization dynamics. Nat. Nanotech. 15 p.356-360 (2020) [2] A. Fernández-Pacheco et al., Three-dimensional nanomagnetism. Nat. Comm. 8 p.15756 (2017) [3] S. Da Col et al., Observation of Bloch-point domain walls in cylindrical magnetic nanowires. Phys. Rev. B. 89 p.180405 (2014) [4] R. Wieser et al., Current-driven domain wall motion in cylindrical nanowires. Phys. Rev. B. 82, p.1-7 (2010) [5] M. Schöbitz et al. Fast Domain Wall Motion Governed by Topology and Œrsted Fields in Cylindrical Magnetic Nanowires. Phys. Rev. Lett. 123 p.217201 (2019) [6] A. De Riz et al. Mechanism of current-assisted Bloch-point wall stabilization for ultra fast dynamics. arxiv: 2011.14869v1

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/dad38862b68e88e07ac7345f1feba12e.jpg)
Figure 1: (a) Time resolved imaging of the tilting of magnetization in cylindrical NWs due to an applied Oersted field with white arrows indicating the direction of the Œrsted field. (b) Tilt angle calculated from the magnetic images for three different NW diameters and compared with theoretical predictions.

![](https://assets.underline.io/uploads/markdown_image/1/image/266b1bac51bb6fd30599e47d72aee2f6.jpg)
Figure 2: (a) Time resolved images of the compression (a) and expansion (b) of a Bloch-point DW in cylindrical NWs due to an applied Oersted field. Illustrations of the compressed (c) and expanded (d) DW from (a,b) with the Oersted field direction indicated.

 Time resolved imaging of Œrsted field induced magnetization dynamics in cylindrical magnetic nanowires

Spin waves are collective excitations of a spin system, where the magnetic moments precess with a spatially periodic phase shift that determines the wavelength [1]. From a technological point of view, the use of spin waves as signal carriers in future spintronic logic and memory devices has the advantages of a potentially lower power consumption and improved miniaturization prospects compared to the present charge-based CMOS technology [2]. For achieving nanoscale integration, topological spin textures such as magnetic vortex cores can be driven by alternating magnetic fields to excite coherent spin waves with short, sub-micrometer wavelengths, as shown recently for both synthetic ferrimagnetic systems and single ferromagnetic layers [3, 4]. In this contribution, we will demonstrate the versatility of this excitation mechanism by showing that the application of a static magnetic bias field makes the vortex core a manipulable spin-wave source that can be continuously translated in space without altering the resulting spin-wave dispersion relation [5]. We employ time-resolved scanning transmission x-ray microscopy (TR-STXM) to directly image vortex-core spin textures as well as the emission and propagation of spin waves from them. By applying a static in-plane magnetic bias field, we can continuously displace the vortex core from its equilibrium position in the center of a structured element. For a synthetic ferrimagnet (Co/Ru/Ni81Fe19), it is possible to shift the core relatively close to the edge while maintaining a radial, isotropic spin-wave emission pattern (see Figure 1). The wavelengths of the excited spin waves are not noticeably changed by the applied magnetic bias field, but remain tunable by the driving frequency in the same way as without bias field. For a single Ni81Fe19 layer with a thickness of the order of 100 nm, we observe a similar behavior for relatively small magnetic bias fields but when the vortex core approaches the edge of the disk, it also expands (see Figure 2). This expansion can be seen as a transformation from a zero-dimensional point source to a one-dimensional curved object where its shape and extent is controlled by the magnitude of the applied magnetic bias field. Such an expansion leads to a directional emission of the spin waves that propagate away from the core in mainly two opposite directions rather than radially as observed for non-expanded cores. For certain combinations of magnetic bias fields and driving frequencies, focusing effects appear. Such effects provide promising means for a controlled and directional propagation of spin waves without the need for additional patterning or waveguides.

**References:**

[1] A.G. Gurevich and G.A. Melkov, Magnetization Oscillations and Waves. Vol. 1, CRC Press (1996) [2] A.V. Chumak et al., Nat. Phys. Vol.11, p.453-461 (2015) [3] S. Wintz et al. Nat. Nanotechnol. Vol.11, p.948-953 (2016) [4] G. Dieterle et al., Phys. Rev. Lett. Vol.122, p.117202 (2019) [5] S. Mayr et al., Nano Lett. accepted (2021)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/1ab356e578b624eb1b59b9aeeb5b4f0a.jpg)
Fig. 1: TR-STXM snapshots of a synthetic ferrimagnet, taken with out-of-plane magnetic sensitivity at the Fe L3 edge at a magnetic bias field of 5 mT. (a) Absolute absorption image showing the black vortex core shifted from the center of the structure (green circle). (b) Normalized contrast displaying the radial spin-wave emission from the core for a 1 GHz alternating field excitation.

![](https://assets.underline.io/uploads/markdown_image/1/image/2d254de94235b1183f441f680c4fed5a.jpg)
Fig. 2: TR-STXM images with out-of-plane sensitivity displaying the response of the vortex in a Ni81Fe19 layer to a magnetic bias field of 22.5 mT. (a) Absolute absorption image showing the expansion of the vortex core (encircled in green). (b) Normalized image displaying only the temporal changes with respect to the average magnetization, showing the spin waves emitted from the expanded vortex core in two directions for an excitation frequency of 8.6 GHz.

 Spin-wave emission from vortex cores under static magnetic bias fields

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

Bottom-up fabrication of magnetic nanostructures composed of particles with desired sizes and composition can result in significant magnetic properties desired for practical applications in high performing magnetics, spintronics, and magnetic sensors [1, 2]. Magnetic and magneto-transport properties are strongly size-dependent, and the ability to adjust nanoparticle size leads to a high control on nanostructures' behavior [3, 4]. Generation of nanoparticles by aerosol methods provides great control of particle formation, size and deposition [5, 6]. Here, we present a novel bottom-up approach for generating self-assembled magnetic nanostructures [7]. The method uses an aerosol technique based on spark ablation to produce nanoparticles (NPs) with tunable compositions guided onto any substrate of choice using combined electric and magnetic fields. Using external magnetic fields, magnetic NPs can be assembled one-by-one along any direction to form 1, 2, or 3-D structures, see Fig. 1. In these systems, both shape and magneto-crystalline contributions play a key role in the magnetic anisotropy resulting in enhanced magnetic properties such as higher coercivity [8]. The presented technique provides a new approach for self-assembling of 1, 2, and 3-D magnetic nanostructures with building blocks that can be tailored for a specific application. Fig. 1 (a-c) shows the magnetic-field-induced self-assembly of vertical and in-plane structures. The magnetic field used to control the self-assembly also aligns the easy axis of the NPs, resulting in a higher anisotropy compared to a chain with randomly oriented particles. Fig. 1 (d) shows the possibility of particle size modulation, which is similar to diameter modulation in magnetic nanowires [9]. As illustrated in Fig. 1 (e), these structures can be directly integrated on the suitable substrates for, e.g., transport measurements or practical applications, which suggests a great advantage over the common solution-based methods [10]. Furthermore, the particle generation technique can be used to generate a vast number of material systems that can be used as building blocks. We have produced nanochains (NCs) composed of Ni, Fe, Co [7, 11], and as shown in Fig. 1 (f, g), CoPd (alloy) and CoAu (segmented/1D granular) structures. By tuning the segmented structures or chemical composition of alloys, a variety of systems can be achieved with possible applications in magnetism and spintronics [5]. Fig. 2 shows the NCs transferred to a carbon-supported copper grid where they were imaged using SEM (a & d) and by Scanning Transmission X-ray Microscopy (STXM) using circular polarized X-rays. The measurements were performed at the PolLux beamline at the Swiss light source (SLS) [12]. X-ray magnetic circular dichroism (XMCD) provides magnetic contrast (b-c & e-f) with a resolution approaching that of a single particle when combined with SEM images from the same NC. Applying a strong ex-situ magnetic field produces a mostly homogeneous remanent magnetization along the NCs with only minor indications of domain formation. Applying an in-situ field of -140 mT resulted in that the XMCD contrast of several more regions along the NC turned bright. These results demonstrate that an ex-situ field can produce a strong remanent magnetization and that the weak in-situ fields can be used to switch the magnetization in some regions. It is argued that these observations are due to larger multi-domain particles that behave as nucleation centers to initiate domain formation. As shown in Fig. 2 (g), micromagnetic simulations on NCs show that the magnetization is energetically favorable along the long axis of the chains and in the same direction (single domain). However, when there is a particle with a diameter larger than the single domain size, the NC breaks up into two domains. Magneto-transport in these structures is of interest since the magnetized and demagnetized states of the chains can result in a magnetoresistance response, and also, the segmented chains composed of different materials (Such as Co/Au in Fig. 1) can act as 1-D magnetic multilayers. To investigate the magneto-transport in these systems, NCs are self-assembled directly onto the surface of a Si-chip insulated with SiO2 and pre-patterned with aligned markers. Contacts to the NCs are defined via electron beam lithography and thermal evaporation, and magneto-transport properties along with micromagnetic simulations will be discussed.

**References:**

[1] H. Wang, Y. Yu, Y. Sun, Nano, Vol. 6, p. 1-17 (2011) [2] D. Lisjak, A. J. P. i. M. S. Mertelj, Progress in Materials Science, Vol. 95, p. 286-328 (2018) [3] J. Mohapatra, M. Xing, J. Elkins, Journal of Physics D, Vol. 53, p. 504004 (2020) [4] Z. Xiang, Y Song, D Pan, Journal of Alloys and Compounds, Vol. 744, p. 432-437 (2018) [5] C. Preger, C. Bulbucan, B. O. Meuller, The Journal of Physical Chemistry C, Vol. 123, p. 16083-16090 (2019) [6] J. Fang, , L Schlag, SC Park, Advanced Materials, Vol. 28, p. 1770-1779 (2016) [7] C. Preger, M. Josefsson, R. Westerström, M. E. Messing, Nanotechnology (Submitted Article) (2021) [8] S. Singamaneni, V. N. Bliznyuk, C. Binek, Journal of Materials Chemistry, Vol. 21, p. 16819-16845 (2011) [9] L. A. Rodríguez, C. Bran, D Reyes," ACS nano, Vol. 10, p. 9669-9678 (2016) [10] X. Chen, Z. Zhou, H. E. Karahan, Small, Vol. 14, p. 1801929 (2018) [11] A. Schmidt-Ott, Spark Ablation: Building Blocks for Nanotechnology. CRC Press (2019) [12] J. Raabe, G Tzvetkov, U Flechsig, Review of scientific instruments, Vol. 79, p. 113704 (2008)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c295a21c34ef6fdff44b2922c6d85a95.jpg)
Fig. 1. SEM image of a single vertical nanochain (NC) (a), 2-D chains along the surface of the substrate (b), and 3-D self-assembly of Co nanoparticles (c). Nanochains with particle-size modulation (d), direct integration of NCs on a Chip (e). EDS (energy-dispersive X-ray spectroscopy) mapping of a CoPd alloy (f) and CoAu segmented (g) nanochain.

![](https://assets.underline.io/uploads/markdown_image/1/image/e10ee3f10149d6228d9b0e2b9546b632.jpg)
Fig. 2. SEM image of a nanochain (a) and corresponding XMCD contrast in a field of +140 mT (b) and -140 mT (c). SEM (d) and remanent XMCD contrast after magnetizing ex-situ in +1.5 T (e). XMCD contrast after applying an in-situ field of -140 mT (f). Micromagnetic simulation of a chain composed of magnetic single-domain particles and a chain including a particle larger than the single-domain size.

 Engineered Self-assembled Magnetic Nanochains INVITED

ROB: Recent Advances In Magnetic Imaging

technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 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 tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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For tickets to the event, please register at the following link: https://magnetism.org/registration

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.

**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

**Session chair:** Mingzhong Wu, Colorado State University


GOJ - Metal Spintronics

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: Olivier Fruchart, SPINTEC*

These on-demand presentations are available to view at your leisure. 

AA: Progress and Prospects of Advanced Magnetic Microscopies

INTERMAG 2021 Welcome Video



	
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Want to buy a ticket? 

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Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

*Session Chair: Oksana Chubykalo-Fesenko, Instituto de Ciencia de Materiales de Madrid, CSIC*

These on-demand presentations are available to view at your leisure.

DD: Magnetism in Curvilinear and Cylindrical Geometries

*Session Co-Chair: Satoshi Iihama, Tohoku Daigaku*

*Session Co-Chair: Sergiu Ruta, University of York*

These on-demand presentations are available to view at your leisure.

ED: Magnon Spintronics

*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 Chair: Tomoyuki Ogawa, Tohoku Daigaku*

These on-demand presentations are available to view at your leisure.

Winner of the Best Student Presentation Award:  ***JI-05 - Non-planar geometrical effects on the magnetoelectrical signal in a 3D nanomagnetic circuit***

Simone Finizio

10

17

SHORT BIO

Presentations

Three Dimensional Nucleation Kinetics Through the First

Current Driven Domain Wall Motion in a Synthetic Antiferromagnet Multilayer

Direct X-ray detection of the spin Hall effect in CuBi

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

Current-Driven Domain Wall Motion in a Synthetic Antiferromagnet Multilayer

Imaging 3D magnetic configurations with X-rays

Time resolved imaging of Œrsted field induced magnetization dynamics in cylindrical magnetic nanowires

Spin-wave emission from vortex cores under static magnetic bias fields

Skyrmions in chiral magnetic multilayers

Engineered Self-assembled Magnetic Nanochains INVITED

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