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The year 2021 was still overshadowed by waves of the COVID-19 pandemic, although the arrival of efficient vaccinations together with the experience of the preceding year gave us a certain routine in handling the situation. By now the execution of meetings in an online mode using zoom and similar video conference systems has been recognized as actually being useful in certain situations, e.g. instead of flying across Europe to attend a three-hours meeting, but also to be able to attend seminars of distinguished scientists which otherwise would not be easily accessible. The scientific productivity of the institute has remained on a very high level, counting 190 publications with an unprecedented average impact factor of 8.0. Six outstanding and representative publications are reprinted in this Annual Report. 16 new third-party projects were granted, among them 7 DFG projects, but very remarkably also an EU funded project on nonlinear magnons for reservoir computing with industrial participation of Infineon Technologies Dresden and GlobalFoundries Dresden coordinated by Kathrin Schultheiß of our Institute. The scientific success was also reflected in two HZDR prizes awarded to the members of the Institute: Dr. Katrin Schultheiß received the HZDR Forschungspreis for her work on “Nonlinear magnonics as basis for a spin based neuromorphic computing architecture”, and Dr. Toni Hache was awarded the Doktorandenpreis for his thesis entitled “Frequency control of auto-oscillations of the magnetization in spin Hall nano-oscillators”. Our highly successful theoretician Dr. Arkady Krasheninnikov was quoted as Highly Cited Researcher 2021 by Clarivate. The new 1-MV facility for accelerator mass spectrometry (AMS) has been ordered from NEC (National Electrostatics Corporation). Design of a dedicated building to house the accelerator, the SIMS and including additional chemistry laboratories for enhanced sample preparation capabilities has started and construction is planned to be finished by mid 2023, when the majority of the AMS components are scheduled for delivery. In the course of developing a strategy for the HZDR - HZDR 2030+ Moving Research to the NEXT Level for the NEXT Gens - six research focus areas for our institute were identified. Concerning personalia, it should be mentioned that the long-time head of the spectroscopy department PD Dr. Harald Schneider went into retirement. His successor is Dr. Stephan Winnerl, who has been a key scientist in this department already for two decades. In addition, PD Dr. Sebastian Fähler was hired in the magnetism department who transferred several third-party projects with the associated PhD students to the Institute and strengthens our ties to the High Magnetic Field Laboratory, but also to the Institute of Fluid Dynamics. Finally, we would like to cordially thank all partners, friends, and organizations who supported our progress in 2021. First and foremost we thank the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Ministers of Education and Research, and of Economic Affairs and Climate Action of the Federal Government of Germany. Many partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank all members of our institute for their efforts in these very special times and excellent contributions in 2021.

Nonvolatile and energy-efficient spin-based technologies call for new prospects to realize computation and communication devices that are able to operate at terahertz (THz) frequencies. In particular, the coupling of electro-magnetic radiation to a spin system is a general requirement for future communication units and sensors. Here we propose a layered metallic system, based on a ferromagnetic film sandwiched in between two heavy metals that allows a highly effective coupling of millimeter wavelength THz light to nanometer-wavelength magnon modes. Using single-cycle broadband THz radiation we are able to excite spin-wave modes with a frequency of up to 0.6 THz and a wavelength as short as 6 nm. Our experimental and theoretical studies demonstrate that the coupling originates solely from interfacial spin-orbit torques. These results are of general applicability to magnetic multilayered structures, and offer the perspective of coherent THz excitation of exchange-dominated nanoscopic magnon modes.

Spin-orbit phenomena enable new ways to manipulate magnetic ordering in low dimensional magnetism. In this respect, materials with antiferromagnetic (AFM) coupling attract significant attention providing higher eigenfrequencies, a rich diversity of material properties and perspectives of spatial scaling due to the absence of significant stray fields. Tailoring the geometry of AFM thin films and nanowires in planar or 3D architectures provides a possibility for changing magnetic responses by means of shape of the magnet [1,2]. In this presentation, we will discuss the recently discovered chiral and anisotropic effects peculiar for curvilinear 1D antiferromagnetic spin chains. A spin chain arranged along a space curve is a prototypical example of a curvilinear AFM whose shape is characterized by the curvature and torsion. In the absence of intrinsic anisotropy, the dipolar interaction renders the tangential direction as the hard axis of the anisotropy [3]. The competition of this geometry-tracking interaction with the nearest-neighbor exchange leads to the emergence of additional anisotropic and chiral energy terms, whose coefficients are determined by the curvature and torsion. The geometry-induced anisotropy is of easy-axis type and determines the direction of the AFM order parameter within the easy-plane enabled by the dipolar interaction. The geometry-induced inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) renders the curvilinear spin chain acting as a chiral helimagnet. The latter leads to the geometrically-driven helimagnetic phase transition in helix-shaped AFM spin chains [3]. A local variation of the anisotropy axis can result in the non-collinearity of the neighboring spins in curvilinear spin chains. 1D AFMs exhibit the parity-breaking effect, which forbids exchanging sublattices once they are selected. This leads to the emergent magnetization at non-collinear AFM textures Therefore, in any spin chain arranged along a space curve, there is a weak ferromagnetism proportional to the curvature and torsion of the curve [4]. Spin chains arranged on a planar surface have the only ground state along the binormal direction [3]. In presence of an external magnetic field, their spin-flop state is dependent on geometrical parameters. The spin-reorientation transition is followed by the canted state for small enough rings due to the exchange-driven DMI. Furthermore, we will show that the curvature-induced DMI results in the hybridization of spin wave modes and enables a geometrically-driven local minimum of the low frequency branch, which opens exciting perspectives to study long-lived collective magnon states in AFMs [3]. This positions curvilinear 1D antiferromagnets as a novel platform for the realization of geometrically tunable chiral antiferromagnets for antiferromagnetic spinorbitronics and fundamental discoveries in the formation of coherent magnon condensates in the momentum space.

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile interaction [4]. Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The major limitation remains primarily due to the use of in-plane magnetized layer stacks, sensitive mainly to the magnetic fields oriented within the sensor plane. This prevailing in-plane sensitivity has prevented them from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane. Flexible Hall effect sensors [5, 6] could provide out-of-plane sensitivity, but not intrinsic logic functionality. In this work, we present the very first tunable magnetoreceptive platform for on-skin touchless interactive electronics based on flexible spin valve switch elements with dedicated out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible polyethylene naphthalate (PEN) foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible device retain its performance upon bending down to 3.5 mm bending radii and withstand more than 600 bending cycles. We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. Depending on the material properties of the on-skin switch used, the virtual functions can be impervious to (latching) or controlled by (momentary) ambient magnetic stimuli. We envision that this technology platform will pave the way towards magnetoreceptive humanmachine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

This dataset contains the numerical data for our publication "Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study" published in Physical Review B. The data consists of dispersion, magnetization ground states and mode profiles of spin waves in vortex-state magnetic nanotubes of different thicknesses, and has been calculated with the TetraX micromagnetic modeling package. All calculations are described within each subfolder by a jupyter notebook.

Asymmetric ultrathin magnetic thin films represent intriguing materil platforms, which support emerging fundamentals effects, such as skyrmion and topological [1] Hall effects and fast motion of chiral magnetic non-collinear textures [2], that underlie prospective memory and logic devices based on spin-orbit torques. Such asymmetric stacks can provide strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interactions (DMI), which is necessary for the sabilization of chiral non-collinear magnetic textures. As the performance of spin-orbitronic devices is determined by the static and dynamic micromagnetic parameters [3], it is crucial to determine all internal micromagnetic parameters for the particular layer combination and sample geometry. In particular, the speed of a domain wall (DW) based racetrack is determined by the DMI constant, $D$, and the DW damping parameter, $\alpha$. The necessity of having strong DMI requires the utilization of ultrathin magnetic (~1 nm) layers, which implies polycrystalinity and compromized structural quality, that substantially enhances the magnetic damping compared to bulk. Accessing this parameters typically requires dynamic experiments, whose interpretations are cumbersome due to the creep regime. Here, we present the experimental and theoretical investigation of tilted DWs in perpendicularly magnetized asymmetric //CrOx/Co/Pt layer stacks with the surface-induced DMI. We will discuss two possible theoretical mechanism for the appearance of titled DWs: (I) A unidirectional tilt could appear in equilibrium as a result of the competition between the DMI and additional in-plane easy-axis anisotropy, which breaks the symmetry of the magnetic texture and introduce tilts [4]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for DWs [5]. A moving DW can be trapped in a tilted state after the external driving field is off. Based on these theoretical approaches, we perform a statistical analysis of the DW tilt angles obtained in staticts after the external magnetic field used for the sample demagnetization was off. We found that the second approach confirms the experimental observations and allows to determine self-consistently the range of DW damping parameters and DMI constants for the particular layer stack. Using two reference fields, which provide two characteristic tilt angles, allow us to retrieve the range of DMI strength $D \geq 0.8$ mJ/m2 and DW damping parameters $\alpha \geq 0.1$. The upper limit for the DMI constant agrees with an independent transport-based measurement giving $D=0.90 \pm 0.13$ mJ/m2, which further refines our estimate of the damping parameter $\alpha=0.13 \pm 0.02$. Thus, the combination of the proposed method with standard metrological techniques opens up opportunities for the quantification of both static and dynamic micromagnetic parameters based on static measurements of the DW morphology. [1] N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions”, Nat. Nanotechnol. 8, 899 (2013). [2] A. Fert, N. Reyren, and V. Cros, “Magnetic skyrmions: advances in physics and potential applications”, Nat. Rev. Mater. 2, 17031 (2017). [3] C. Garg, S.-H. Yang, T. Phung, A. Pushp and S. S. P. Parkin, “Dramatic influence of curvature of nanowire on chiral domain wall velocity”, Sci. Adv. 3, e1602804 (2017). [4] O. V. Pylypovskyi, V. P. Kravchuk, O. M. Volkov, J. Fassbender, D. D. Sheka and D. Makarov, “Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction”, J. Phys. D: Appl. Phys. 53, 395003 (2020). [5] O. M. Volkov, F. Kronast, C. Abert, E. Se. Oliveros Mata, T. Kosub, P. Makushko, D. Erb, O. V. Pylypovskyi, M.-A. Mawass, D. Sheka, S. Zhou, J. Fassbender and D. Makarov, “Domain-Wall Damping in Ultrathin Nanostripes with Dzyaloshinskii-Moriya Interaction”, Phys. Rev. Appl. 15, 034038 (2021).

As for everybody else also for the Institute of Ion Beam Physics and Materials Research (IIM), the COVID-19 pandemic overshadowed the usual scientific life in 2020. Starting in March, home office became the preferred working environment and the typical institute life was disrupted. After a little relaxation during summer and early fall, the situation became again more serious and in early December we had to severely restrict laboratory activities and the user operation of the Ion Beam Center (IBC). For the most part of 2020, user visits were impossible and the services delivered had to be performed hands-off. This led to a significant additional work load on the IBC staff. Thank you very much for your commitment during this difficult period. By now user operation has restarted, but we are still far from business as usual. Most lessons learnt deal with video conference systems, and everybody now has extensive experience in skype, teams, webex, zoom, or any other solution available. Conferences were cancelled, workshops postponed, and seminar or colloquia talks delivered online. Since experimental work was also impeded, maybe 2020 was a good year for writing publications and applying for external funding. In total, 204 articles have been published with an average impact factor of about 7.0, which both mark an all-time high for the Institute. 13 publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute. In addition, 20 new projects funded by EU, DFG, BMWi/AiF and SAB with a total budget of about 5.7 M€ have started. Thank you very much for making this possible. Also, in 2020 there have been a few personalia to be reported. Prof. Dr. Sibylle Gemming has left the HZDR and accepted a professor position at TU Chemnitz. Congratulations! The hence vacant position as the head of department was taken over by PD Dr. Artur Erbe by Oct. 1st. Simultaneously, the department has been renamed to “Nanoelectronics”. Dr. Alina Deac has left the institute in order to dedicate herself to new opportunities at the Dresden High Magnetic Field Laboratory. Dr. Matthias Posselt went to retirement after 36 years at the institute. We thank Matthias for his engagement and wish him all the best for the upcoming period of his life. However, also new equipment has been setup and new laboratories founded. A new 100 kV accelerator is integrated into our low energy ion nanoengineering facility and complements our ion beam technology in the lower energy regime. This setup is particularly suited to perform ion implantation into 2D materials and medium energy ion scattering (MEIS). Finally, we would like to cordially thank all partners, friends, and organizations who supported our progress in 2020. First and foremost we thank the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Ministers of Education and Research, and of Economic Affairs and Energy of the Federal Government of Germany. Many partners from univer¬sities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank all members of our institute for their efforts in these very special times and excellent contributions in 2020.

The X/Co 3nm/Y (where X, Y=Au, Pt) trilayers with as deposited in-plane magnetization alignment were irradiated with 30 keV Ga+ ions in the wide range of ion fluence. The samples were investigated by means of complementary techniques: magneto-optical magnetometry and spectroscopy (in the photon energy range from 1.2 eV to 4.5 eV), magnetic force microscopy, positron annihilation spectroscopy, X-ray diffraction and reflectivity. Difference in miscibility of interface atoms is clearly manifested in various intermixing extent at Co/Pt and Co/Au interfaces and consequently in magnetic properties of the irradiated trilayers. Low irradiation fluence (~1014 ions/cm2) leads to ~1nm interfaces broadening without visible surface etching for all samples, which is related with a distinct drop of magnetic anisotropy. However, the high irradiation fluence (~5·1015 ions/cm2) results in enhanced interface broadening and significant surface etching (~5 nm) partially removing also Co atoms. Tensile strains (up to 0.5%) were developed in the cover layers. The tensile strain, layers intermixing and the creation of Co-Pt(Au) alloys with different composition formed by irradiation are correlated with the increase of magnetic anisotropy. Moreover it was observed that substitution of Au instead of Pt (as a cap or buffer layer) results in substantial increase of perpendicular magnetic anisotropy. Maximal increase of magnetooptical parameters was observed for Pt/Co/Pt layer. Irradiation induced changes of concentration profiles are revealed using magnetooptical spectra, X-ray reflectivity spectra and simulations with use of binary collision approximation.

The tuning and control over the intrinsic magnetic properties, such as saturation magnetization (Ms) and Gilbert damping (α), can be obtained via systematic rearrangement of the lattice at the nanoscale. In certain binary alloys such as B2 Fe60Al40 [1] and B2 Fe50Rh50 [2], the Ms can be tuned by inducing chemical disorder. The disorder caused by the randomization of site occupancies of the atoms can be achieved by ion-irradiation. Here we explore a magnetic phase transition in Fe60V40 thin films caused by ordering of the lattice structure from short-range order to the crystalline state. Fe60V40 films (~ 40 nm) were grown onto SiO2/Si substrate. The as-grown films are weakly ferromagnetic with low Ms of 17 kA/m; whereas irradiation with 25 keV Ne+-ions at fluences of ~ 5 × 1015 ions/cm2 leads to a drastic increase of Ms to ~ 750 kA/m, as shown in Fig. 1. X-ray diffraction as well as transmission electron microscopy reveal a structural short-range order in the as-grown films, that transform to A2 Fe60V40 with increasing Ne+-fluence. The A2 region appears to nucleate at the film top surface and with increasing fluence, it propagates deeper down into the film. The effect of the phase transition on the dynamic behaviour has been investigated using ferromagnetic resonance (Fig. 2). The low value of Gilbert damping (~ 0.002) has been obtained from the frequency dependence of the resonance spectra. Furthermore, the transition can be tracked using Conversion electron Mössbauer spectroscopy to shed light on the variation of local magnetic ordering during the transition. The tunable film structure as well as low damping form the basis for further investigations on nanomagnets embedded within Fe60V40 thin films. Funding by the DFG - 322462997 (BA 5656/1-2 | WE 2623/14-2) is acknowledged. Ion-irradiation was performed at the Ion Beam Centre of the HZDR. References [1] J. Ehrler, et al., New J. Phys., 22, 073004 (2020). [2] B. Eggert, et al., RSC Adv.,10, 14386 (2020).

Antiferromagnets are technologically promising materials for spintronic and spinorbirtonic devices [1]. An efficient manipulation of antiferromagnetic textures requires the presence of the Dzyaloshinskii-Moriya interaction (DMI), which is present in crystals of special symmetry, and thus limits the number of available materials. In contrast to antiferromagnets, it is already established that in ferromagnetic thin films and nanowires chiral responses can be tailored relying on curvilinear geometries [2]. Here, we explore geometry-induced effects in curvilinear antiferromagnets. We demonstrate theoretically that intrinsically achiral curvilinear antiferromagnetic spin chains behave as a biaxial chiral helimagnet with a curvature-tunable anisotropy and DMI [3]. The geometry-driven easy axis anisotropy determines the homogeneous antiferromagnetic state at low curvatures and the gap for spin waves. The geometry-driven DMI determines the helimagnetic phase transition and leads to the appearance of the region with the negative group velocity at the dispersion curve. [1] V. Baltz et al., Rev. Mod. Phys. 90, 015005 (2018). [2] R. Streubel et al., J. Phys. D.: Appl. Phys. 49, 363001 (2016). [3] O. V. Pylypovskyi et al., Nano Lett. (2020) DOI: 10.1021/acs.nanolett.0c03246.

Asymmetrically sandwiched thin magnetic layers with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction (DMI) is the prospective material science platform for spin-orbitronic technologies that rely on the motion of chiral magnetic textures, like skyrmions or chiral domain walls (DWs). The dynamic performance of a DW-based racetracks is defined by the strength of DMI and the DW damping. The determination of the latter parameter is typically done based on technically challenging DW motion experiments. Here, we propose a method to access both parameters, DMI constant and DW damping, yet in static experiments by monitoring the tilt of magnetic DWs in nanostripes. We experimentally demonstrate that in perpendicularly magnetized //CrO x /Co/Pt stacks, DWs can be trapped on edge roughness in a metastable tilted state as a result of the DW dynamics driven by external magnetic field. The measured tilt can be correlated to the DMI strength and DW damping in a self-consistent way in the frame of a theoretical formalism based on the collective coordinate approach.

Curvilinear magnetic objects are in focus of intensive research due to the possibility to obtain new fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. In geometrically-broken magnetic objects all energy functionals, that contains spatial derivatives, e.g. exchange, magnetostatic and intrinsic Dzyaloshinskii-Moriya (DMI) interactions, are reshaping in a way of appearance additional curvature-induced chiral and anisotropy terms. These novel chiral magnetic responses arise in the physical space, by introducing bends and twists to magnetic architectures even of conventional materials. We address both experimentally and theoretically the appearance of curvature-induced exchange effects in parabolic nanostripes with different geometrical parameters [2]. We show that a pinning of transversal domain wall at the parabolic apex is originated due to the presence of local curvature-induced DMI that creates a subsequent pinning potential. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. In its turn, the interplay between the intrinsic and exchange-induced DMI paves the way to a mesoscale DMI, whose symmetry and strength depend both on the geometrical and material parameters [3]. Developing this concept we propose a novel approach towards artificial ME materials with helimagnetic nanohelices embedded in a piezoelectric matrix [4]. By applying an electric field, small geometrical changes of pitch and radius could lead to the phase transition from a homogeneously magnetized state (full average magnetic moment) to a periodical one (zero average magnetic moment). [1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016). [2] O. Volkov et al.. Phys. Rev. Lett. 123, 077201 (2019). [3] O. Volkov et al., Sci. Rep. 8, 866 (2018). [4] O. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Understanding of the interaction of antiferromagnetic solitons including domain walls and skyrmions with boundaries of chiral antiferromagnetic slabs is important for the design of prospective antiferromagnetic spintronic devices. Here, we derive the transition from spin lattice to micromagnetic nonlinear $��$-model with the corresponding boundary conditions for a chiral cubic G-type antiferromagnet and analyze the impact of the slab boundaries and antisymmetric exchange (Dzyaloshinskii--Moriya interaction) on the vector order parameter. We apply this model to evaluate modifications of antiferromagnetic domain walls and skyrmions upon interaction with boundaries for different strengths of the antisymmetric exchange. Due to the presence of the antisymmetric exchange, both types of antiferromagnetic solitons become broader when approaching the boundary and transform to a mixed Bloch--N��el structure. Both textures feel the boundary at the distance of about 5 magnetic lengths. In this respect, our model provides design rules for antiferromagnetic racetracks, which can support bulk-like properties of solitons., 12 pages, 5 figures, 71 reference

Ultra-portable, imperceptible[1], and shapeable[2] devices are expected to be widespread due to the emergence of flexible electronics as an industrial technology. Printing is an affordable and high throughput method to process electronics in soft substrates that is still to be optimized to deliver electrically and mechanically reliable electronic devices[3]. In particular, printable magnetoresistive pastes have been developed as an alternative single-step fabrication method to obtain magnetic field sensors [4]. These pastes usually consist of composites of magnetic particles embedded in a non-magnetic matrix[5,6]. Particle-based pastes can achieve large magnetoresistance ratios at the expense of high resistivity and noise levels[5-7]. We previously reported magnetoresistive pastes based on microflakes as an alternative to overcome the problems presented in particle-based pastes[8,9]. Magnetoresistive flakes were produced after the delamination of thin-film stacks from a deposited sacrificial layer. With this technology, it was showed that flakes-based Co/Cu printed sensors exhibit low resistance and 37% GMR response at moderate magnetic fields (500 mT)[9]. Despite the advances in printable magnetic sensors, there are no reports of systems that show good sensitivity at low magnetic fields relevant for safe integration into consumer and wearable electronics. Electronics with magnetic components have to perform below the WHO limit of continuous exposure to magnetic fields (

A complex structure of magnetic subsystem in antiferromagnets (AFMs) determines challenges and technological perspectives for both, fundamental research and their applications for spintronic and spin-orbitronic devices [1]. In this respect, properties of the confined samples are of key interest because of the possibility to tune magnetic responses via effects of boundary and geometrical curvature [2]. Here, we consider textures in (i) AFM slabs with the Dzyaloshniskii-Morya interaction (DMI) of bulk symmetry [3] and (ii) the intrinsically achiral curvilinear spin chains arranged along space curves [4]. We derive a transition from spin lattice of G-type AFM to the sigma-model with the respective boundary conditions for the AFM order parameter [3]. The DMI influences a texture via boundary conditions modifying the ground state, domain wall shape and skyrmion profiles. Approaching the boundary in the slab with easy-axis anisotropy, the domain wall becomes broader and of mixed Bloch-Neel type near the top surface. Near the edges of the sample, the domain wall plane possesses and additional twist. Note, that the edge twists appear in achiral AFMs as well if the domain wall plane lies at an angle to the side faces [5]. Similarly, skyrmions of any radius become of the Bloch-Neel type approaching the top/bottom surfaces of the sample. The radius of narrow skyrmions changes up to 10% due to the boundary effects. AFM spin chains arranged along space curves can model the simplest curvilinear nanoarchitectures. Their geometry is described by the curvature and torsion, determining local bends and twists of the curve. The geometry-driven anisotropy and inhomogeneous DMI render them as chiral helimagnets [6]. In addition, the exchange interaction generates the weakly ferromagnetic response, scaling linearly with curvature and torsion. The inter- and single-ion anisotropies in curvilinear AFM chains lead to the additional anisotropic contributions, scaling with curvature. The single-ion anisotropy leads to the homogeneous DMI mixing normal and tangential components of ferro- and antiferromagnetic vector order parameters. Both anisotropy models contribute to the additional easy axes, which determine the direction of the order parameters in spin-flop phase [4]. [1] V. Baltz et al, Rev. Mod. Phys. 90, 015005 (2018); A. Manchon et al, Rev. Mod. Phys. 91, 035004 (2019) [2] P. Fischer et al, APL Mat. 8, 010701 (2020); R. Streubel et al, J. Appl. Phys. 129, 210902 (2021); D. D. Sheka, Appl. Phys. Lett. 118, 230502 (2021) [3] O. V. Pylypovskyi et al, Phys. Rev. B 103, 134413 (2021) [4] O. V. Pylypovskyi et al, Appl. Phys. Lett. 118, 182405 (2021) [5] N. Hedrich et al, Nat. Phys. 17, 574 (2021) [6] O. V. Pylypovskyi, D. Y. Kononenko et al, Nano Lett. 20, 8157 (2020)

Curvilinear magnetism is the emerging field in micromagnetism which studies influences of external geometry and its topology on magnetic vector fields [1]. Much attention was paid to fundamental theoretical investigations of curvature-induced effects for local [2,3] and non-local magnetic interactions [4], which results in the prediction of various magnetochiral effects [2,5], topologically-induced magnetic patterns [5,6], stabilization of individual skyrmions [7,8] and skyrmion lattices [9] on curvilinear defects. Recently, we provided the very first experimental confirmation and quantitative assessment of the existence of the curvature-induced chiral interaction of exchange origin in a conventional soft ferromagnetic material [10]. In its turn, the interplay between the intrinsic and exchange-induced Dzyaloshinskii-Moriya interaction (DMI) paves the way to a mesoscale DMI [3], whose symmetry and strength depends both on the geometrical and material parameters of the magnetic system. Extending this concept we proposed a novel approach towards artificial magnetoelectric materials with helimagnetic nanohelices embedded in a piezoelectric matrix [11], where electric field could control magnetic states through the utilization of curvature-induced effects. [1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016). [2] Y. Gaididei et al., Phys. Rev. Lett. 112, 257203 (2014). [3] O. Volkov et al., Sci. Rep. 8, 866 (2018). [4] D. D. Sheka et al., Commun. Phys. 3, 128 (2020). [5] V. P. Kravchuk et al., Phys. Rev. B 85, 144433 (2012). [6] O. V. Pylypovskyi et al., Phys. Rev. Lett. 114, 197204 (2015). [7] V. P. Kravchuk et al., Phys. Rev. B 94, 144402 (2016). [8] O. V. Pylypovskyi et al., Physical Review Applied 10, 064057 (2018). [9] V. P. Kravchuk et al., Phys. Rev. Lett. 120, 067201 (2018). [10] O. M. Volkov et al., Phys. Rev. Lett. 123, 077201 (2019). [11] O. M. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Antiferromagnets represent a wide class of technologically promising materials for spintronic and spinorbirtonic devices with multiple magnetic sublattices [1]. An efficient manipulation of antiferromagnetic textures requires the presence of the Dzyaloshinskii-Moriya interaction (DMI), which is present in crystals of special symmetry, and thus limits the number of available materials. In contrast to antiferromagnets, it is already established that in ferromagnetic thin films and nanowires chiral responses can be tailored relying on curvilinear geometries [2]. Here, we explore curvature effects in curvilinear antiferromagnets which are stemming from exchange interaction [3]. It is shown that intrinsically achiral curvilinear antiferromagnetic spin chains behave as a biaxial chiral helimagnet with a curvature-tunable anisotropy and DMI. In contrast to ferromagnetic spin chains, the dipolar interaction leads to the hard-axis anisotropy. This allows to observe the effects of geometry even in chains with small curvature and torsion because of absence of other competing easy axis anisotropies except the geometry-induced one. The latter determines the homogeneous antiferromagnetic state at low curvatures and the gap for spin waves. The geometry-driven DMI determines the helimagnetic phase transition and leads to the appearance of the region with the negative group velocity at the dispersion curve. We note, that the anisotropy in curvilinear antiferromagnetic spin chains is an additional source of geometry-driven effects on magnetic textures [4].

4 páginas, 3 figuras.-- et al., A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks., This work has been partially financed by the Catalan DGR and the Spanish MICINN (Grant Nos. 2009-SGR- 1292, MAT2007-66309-C02, and MAT2007-61629). E.M. thanks the Fund for Scientific Research—Flanders FWO for financial support. M.D.B. was partially supported by an ICREA ACADEMIA award.

Printed electronics are expected to be implemented as a set of industrial technologies that will facilitate the on-demand fabrication of imperceptible[1] and shapeable[2] devices. Conductive pastes are typically composed of polymeric matrices with embedded conductive fillers. The properties of the fillers can be exploited to deliver functional devices as printed transistors[3], displays[4] and sensors[5]. The smart integration of such elements will allow task-specific integration in consumer electronics and even personalized wearable devices. Aiming to develop on-skin printed interfaces, it is necessary to ponder mechanical, performance, and health safety considerations. Integrating magnetic sensors on interactive platforms is attractive due to their touchless, action-at-distance nature, which increases the reliability of the devices[6]. In the past, solution processable magnetic field sensors have been fabricated from composite pastes embedding magnetic particles. Among the previous reports on printable magnetic sensors, there are not examples of devices able to maintain high performance sensing during usual skin deformations[7]. Concomitantly, there is a lack of research on skin-compliant printed magnetic sensors able to perform below the 40 mT safety continuous exposure threshold established by the World Health Organization[8]. Here, we will present the fabrication and implementation of stretchable printed magnetic field sensors. They are based on composite pastes with embedded flakes of [Py/Cu]30 Giant Magnetoresistance (GMR) thin-film stacks. We demonstrated printed GMR sensors on ultrathin (3-µm-thick Mylar) foils which are skin compliant, and with maximum sensitivity at 0.88 mT. The stretchable sensors maintained stable sensing performance at 16 µm bending radius and 100 % strain which corresponds to two orders of magnitude increase with respect to previous reports. We demonstrate the implementation of the technology on interactive applications after laminating the printed sensors on the user's skin to navigate through digital maps and scroll through text documents. The ability of the sensor to comply with the skin creases and deformations, and to detect field changes in the safe threshold limit, place this technology as a prospective method for fabricating on-demand printed human-machine interfaces[9]. [1] M. Melzer et al., Nat. Commun. 6, 6080 (2015) [2] D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016) [3] J.A. Lim et al., Adv. Func. Mater. 20, 3292 (2010) [4] S. Cho et al. ACS Appl. Mater. Interfaces 9, 44096 (2017) [5] X. Wang et al. ACS Appl. Mater. Interfaces 10, 7371 (2018) [6] P. Makushsko et al., Adv. Func. Mater, 2101089 (2021) [7] E.S. Oliveros Mata, et al. Appl. Pys. A 127, 280 (2021) [8] Static Fields. World Health Organization. (2006) [9] M. Ha, E.S. Oliveros Mata, et al. Adv. Mater. 33, 2005521 (2021)

We investigate the evolution of spin polarization, spontaneous Hall angle (SHA), saturation magnetization and Curie temperature of B2-ordered Fe60Al40 thin films under varying antisite disorder, induced by Ne+-ion irradiation. The spin polarization increases monotonically as a function of ion fluence. A relatively high polarization of 46 % and the SHA of 3.1 % are achieved on 40 nm thick films irradiated with 2 ⋅ 1016 ions/cm2 at 30 keV. An interesting divergence in the trends of the magnetization and SHA is observed for low disorder concentrations. The high spin polarization and its broad tunability range make ion-irradiated Fe60Al40 a promising material for application in spin electronic devices.

Magnetization switching using in-plane charge current recently has been widely investigated in heavy metal/ferromagnet bilayers with the switching mechanism usually attributed to the action of the spin-orbit coupling. Here we study in-plane current induced magnetization switching in model epitaxial bilayers that consist of Au(001) and Fe(001) grown on MgO(001). We use the planar Hall effect combined with magnetooptical Kerr effect (MOKE) microscopy to investigate magnetic properties of the bilayers and current-induced switching. We show that a current density beyond 1.4×107 A/cm2 can be employed for reproducible electrical switching of the magnetization between multiple stable states that correspond to different arrangements of magnetic domains with magnetization direction along one of the in-plane easy magnetization axes of the Fe(001) film. Lower current densities result in stable intermediate transversal resistances which are interpreted based on MOKE-microscopy investigations as resulting from the current-induced magnetic domain structure that is formed in the area of the Hall cross. We find that the physical mechanism of the current-induced magnetization switching of the Au/Fe/MgO(001) system at room temperature can be fully explained by the Oersted field, which is generated by the charge current flowing mostly through the Au layer. © 2021 authors. Published by the American Physical Society.

Magnetic field sensors, which can perceive environmental changes with respect to altered magnetic fields, enable proximity sensing ranging from touchless human-machine interaction to noninvasive medical diagnostics. In this regard, magnetic field sensors should be aimed toward perfect mounting on the curved human body and uneven organs without any mechanical constraints, at the same time, pursuing high sensitivity in low magnetic fields at 1 mT for the practical use of wearable electronics to the general public. Here, we demonstrate that high performance giant magnetoresistive (GMR) sensors can be printed on ultrathin 3-µm-thick polymeric foils enabling the mechanically imperceptible magnetoelectronics. Thanks to their excellent compliancy, the printed GMR sensors well adapt to the periodic buckling surface. They constitute the first example of printed GMR sensors, revealing 2 orders of magnitude improvements in mechanical stability and sensitivity at small magnetic fields, compared to the state-of-the-art printed magnetoelectronics [1]. Even when bent to a radius of 16 µm, the sensors screen printed on ultrathin foils remain fully intact and possess high sensitivity of 3 /T in a low magnetic field of 0.88 mT. With this performance, the compliant GMR sensors can be used as components of on-skin interactive electronics as we demonstrate with a touchless control of virtual objects including zooming in and out of interactive maps and scrolling through electronic documents. [1] Meyer, J., Rempel, T., Schäfers, M., Wittbracht, F., Müller, C., Patel, A., Hütten, A., Smart Mater. Struct. 22 (2013) 025032-025037.

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al, thereby imparting a good electrical conductivity, as well as mechanical stability, radiation and oxidation resistance [1, 2]. These properties rely on the lamellar structure of the compound, and systematic introduction of defects, such as displacing or doping atoms within the layers, has the potential to tune electron transport and modify magnetic properties [3]. An ideal tool for defect implantation is ion-irradiation, available both in the form of a broad-beam for wafer-scale processing as well as focused ion-beams for device prototyping. Here we observe the modifications to the structural, transport and magnetic behavior of 500 nm thick Cr2AlC after irradiation with Co+ ions, and Ar+ noble gas ions as control. The films were irradiated with 450 keV of Co+ ions at fluences varying from 5E12 to 5E15 ions.cm-2, and the control samples with 400 keV Ar+ ions keeping the sample fluences. Structural analysis using XRD shows that ion-irradiation induces a suppression of the 0002 reflection, indicating a gradual decay of the nano-lamellar structure. Increasing ion-fluence also leads to an increase of the saturation magnetization at 1.5 K, whereby both Ar+ and Co+ cause an increased magnetization, respectively to 150 and 190 kA.m-1, for the highest fluences used. Large variations of the transport properties are observed. Magnetoresistance (MR) in the non-irradiated sample shows a classical B2 dependency, even up to high temperatures. At Co+ fluences of 5E13 ions.cm-2 the MR shows a two orders of magnitude increase, up to 3% (10 T) at 100 K. A similar effect also occurs for 5E12 ions.cm-2 Ar+ irradiated films, however with a smaller MR-increase. It appears that resistivity increases and the residual resistance ratio reduces with increasing fluence due to the introduction of disorder. These results show that ion irradiation induces significant changes in the transport properties of MAX phase materials, that will be further investigated. The systematic disordering of nano-laminated MAX phase films may therefore reveal interesting disorder and spin-related transport phenomena. Funding by the Deutsche Forschungsgemeinschaft (DFG) - Project number 456078299 is acknowledged. Ion-irradiation has been performed at the Ion Beam Centre of the HZDR. [1] A. S. Ingason, M. Dahlqvist, J. Rosen, Magnetic MAX phases from theory and experiments; a review; J. Phys.: Condens. Matter 28, 433003, (2016). [2] M. W. Barsoum, MAX Phases: Properties of Machinable Ternary Carbides and Nitrides; Weinheim: Willey-VCH (2013). [3] C. Wang, T. Yang, C. L. Tracy, C. Lu, H. Zhang, Y.-J. Hu, L. Wang, L. Qi, L. Gu, Q. Huang, J.Zhang, J. Wang, J. Xue, R. C. Ewing, Y. Wang, Disorder in Mn+1AXn phases at the atomic scale, Nature Communications 10, 622 (2019).

Antiferromagnetic (AFM) materials have distinct advances compared to ferromagnets, that allow to use them in variety of spintronic applications [1,2]. Antiferromagnetically coupled curvilinear spin chains are of fundamental interest as simplest systems possessing interplay between the geometry and magnetic subsystem [3]. In this work, we analyze the ground states of AFM ring-shaped spin chain with the nearest-neighbour Heisenberg exchange and single-ion anisotropy in presence of external magnetic field. The direction of magnetic field coincides with the symmetry axis of the ring. Collinear two-sublattice 1D curved AFM chain with even number of spins is considered, and the hard axis of anisotropy is oriented tangentially to the chain. Within the classical continuum approach its magnetic state is described by two order parameters, the Néel and ferromagnetism vector fields. In the ground state, the Néel vector is oriented perpendicularly to the ring plane. The magnetic field applied along the ring normal allows to observe spin-flop and spin-flip orientational phase transitions. We determine the dependency of spin-flop and spin-flip transition fields on the ring curvature and the critical curvature which separates two topologically different ground states above spin-flop transition. The first one with the Néel order parameter within the normal plane is mainly determined by the anisotropy at small curvatures. The second ground state at large curvatures is represented by onion ordering of the Néel vector. With the applied fields larger than critical spin-flip transition field Néel order parameter vanishes, which leads to ferromagnetic ground state. The phase diagram of AFM as a function of applied field intensity and the ring curvature is developed.

Printed electronics are attractive due to their low-cost and large-area processing features, which have been successfully extended to magnetoresistive sensors and devices. Here, we introduce and characterize a new kind of magnetoresistive paste based on the anisotropic magnetoresistive (AMR) effect. The paste is a composite of 100-nm-thick permalloy/tantalum flakes embedded in an elastomer matrix, which promotes the formation of appropriately conductive percolation networks. Sensors printed with this paste showed stable magnetoresistive properties upon mechanical bending. The AMR value of this sensor is 0.34% in the field of 400 mT. Still, the response is stable and allows to resolve sub-mT field steps. When printed on ultra-thin 2.5-μm-thick Mylar foil, the sensor can be completely folded without losing magnetoresistive performance and mechanically withstand 20 μm bending radius. The developed compliant printed AMR sensor would be attractive to implement on curved and/or dynamic bendable surfaces for on-skin applications and interactive printed electronics.

Antiferromagnets are technologically promising materials for spintronic and spinorbirtonic devices [1]. An efficient manipulation of antiferromagnetic textures requires the presence of the Dzyaloshinskii-Moriya interaction (DMI), which is present in crystals of special symmetry, and thus limits the number of available materials. In contrast to antiferromagnets, it is already established that in ferromagnetic thin films and nanowires chiral responses can be tailored relying on curvilinear geometries [2]. Here, we explore curvature effects in curvilinear antiferromagnets [3]. We demonstrate theoretically that intrinsically achiral curvilinear antiferromagnetic spin chains behave as a biaxial chiral helimagnet with a curvature-tunable anisotropy and DMI. In contrast to ferromagnetic spin chains, this system possesses the hard-axis anisotropy stemming from the dipolar interaction, which allows to observe the effects of geometry even in chains with small curvature and torsion. The geometry-driven easy axis anisotropy determines the homogeneous antiferromagnetic state at low curvatures and the gap for spin waves. The geometry-driven DMI determines the helimagnetic phase transition and leads to the appearance of the region with the negative group velocity at the dispersion curve. [1] V. Baltz et al., Rev. Mod. Phys. 90, 015005 (2018) [2] R. Streubel et al., J. Phys. D.: Appl. Phys. 49, 363001 (2016) [3] O. V. Pylypovskyi, D. Y. Kononenko et al., Nano Lett. 20, 8157 (2020)

Highly compliant electronics, naturally conforming to human skin, represent a paradigm shift in the interplay with the surroundings. Solution-processable printing technologies are yet to be developed to comply with extreme requirements to mechanical conformability of on-skin appliances. Here, it is demonstrated that high-performance spintronic elements can be printed on ultrathin 3 μm thick polymeric foils enabling the mechanically imperceptible printed magnetoelectronics. Benefiting from their extreme compliancy, the printed magnetic-field sensors well adapt to the periodic buckling surface to be biaxially stretched over 100% of strain rate. They constitute the first example of printed and stretchable giant magnetoresistive sensors, revealing 2 orders of magnitude improvements in mechanical stability and sensitivity at small magnetic fields, compared to the state-of-the-art printed magnetoelectronics. The key aspect of this performance enhancement is the use of elastomeric triblock copolymers as a binder for the magnetosensitive paste. Even when bent to a radius of 16 μm, the sensors screen printed on ultrathin foils remain fully intact and possess unmatched sensitivity for printed magnetoelectronics of 3 T-1 in a low magnetic field of 0.88 mT. With this performance, the compliant printed sensors can be used as components of on-skin interactive electronics as it is demonstrated with a touchless control of virtual objects including zooming in and out of interactive maps and scrolling through electronic documents.