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Dieter Suess

Publications and source records attributed to Dieter Suess.

At least 19 recordsLinked to original sources

Perspectives on inverse design for AI magnonics

Inverse design - specifying a desired functionality and letting a computational algorithm find the optimal structure - has emerged as a powerful paradigm for magnonic device engineering. In this article, we survey the rapidly growing field of inverse-design magnonics, organising it along two axes: the design variables (topology, material parameters, and magnetic field landscape) and the algorithmic toolbox (gradient-free, gradient-based, and neural-network-based methods) together with the differentiable micromagnetic solvers that enable them. We then identify open frontiers that we consider most promising for the next phase of the field: sensitivity analysis and robust design to bridge the gap between simulation and experiment; input shaping and transducer optimisation; the incorporation of nonlinear spin-wave effects as an explicit design resource; spatially structured amplification; self-adapting media and machine-learning-based design; and the long-term vision of a universal, reconfigurable magnonic platform. We argue that magnonics and artificial intelligence are converging from two directions - machine-learning tools for designing magnonic devices, and magnonic devices as hardware for neuromorphic computation - and propose the term AI magnonics to describe this emerging paradigm.

cond-mat.mes-hall

Generation of Bloch Points with Controlled Spin Texture Using Geometrical Boundary Conditions

Bloch points are three-dimensional topological singularities in magnetization that play a key role in topological transformations of spin textures, such as skyrmion creation or annihilation. While topology often enforces the existence of Bloch points in confined geometries like cylindrical nanowires, deterministic control over their position and magnetic configuration remains challenging. Here we demonstrate the generation of Bloch points with controlled spin texture by engineering geometrical boundary conditions in three-dimensional nanomagnets. By introducing a chirality interface between two three-dimensional double-helix nanowires of opposite handedness, forming a kinked, non-collinear structure, we impose competing topological constraints that uniquely define the magnetization configuration surrounding the Bloch point. A saturating magnetic field nucleates head-to-head or tail-to-tail domain configurations at the chirality interface, producing a Bloch-point domain wall with deterministic polarity, circulation and helicity. This geometrical approach enables full three-dimensional control of Bloch point domain walls allowing deterministic engineering of their spin texture and its selective coupling to current-induced Oersted fields.

cond-mat.mes-hall

Magnetization alignment in spin-transfer-torque magnetic random-access memory

Reliable operation of perpendicular spin-transfer-torque magnetic random-access memory (p-STT-MRAM) requires control of magnetic alignment within the synthetic antiferromagnet (SAF) reference layer. At nanopillar dimensions, however, devices can exhibit magnetic states that are absent in extended thin films. We present a systematic micromagnetic study of 30 nm-diameter three-layer p-STT-MRAM nanopillars using experimentally motivated material parameters, and map equilibrium states as functions of bilinear and biquadratic interlayer exchange coupling. Phase diagrams show that introducing asymmetry between the SAF layers in saturation magnetization, anisotropy, and thickness reduces the coupling strength required to stabilize antiparallel SAF states and suppress competing configurations. Minimum-energy path calculations show that, for noncollinear antiparallel SAF states, increasing SAF asymmetry can raise SAF reversal barriers while lowering the free-layer barrier; this trade-off is absent for collinear antiparallel SAF states. Stray fields also significantly modify both SAF and free-layer energy barriers. To support the design of p-STT-MRAM devices with either collinear or noncollinear antiparallel SAF reference states, we publicly release the simulation dataset covering 4374 distinct device configurations.

cond-mat.mes-hall

A Fourier-Space Approach to Physics-Informed Magnetization Reconstruction from Nitrogen-Vacancy Measurements

Reconstructing magnetization textures from nitrogen-vacancy (NV) magnetometry stray-field measurements is a challenging, fundamentally ill-posed inverse problem, further complicated by the unknown effective distance between sensor and magnetic material. Here we show that incorporating a micromagnetic energy functional directly into the inversion filters out unphysical, high-energy configurations, while Fourier-space upward continuation of the stray field allows us to simultaneously fit the distance. Applied to measurements of the van der Waals ferromagnet Fe$_{3-x}$GaTe$_2$, it recovers an effective distance estimate of approximately 81nm and low-energy configurations that reproduce the observed field. More broadly, embedding physics directly into the reconstruction turns ill-posed magnetic inverse problems into transparent, interpretable reconstructions, with applicability well beyond NV magnetometry.

cond-mat.mes-hall

Nanoscale spin-wave frequency-selective limiter for 5G technology

Power limiters are essential devices in modern radio frequency (RF) communications systems to protect highly sensitive input channels from large incoming signals. Nowadays-used semiconductor limiters suffer from high electronic noise and switching delays when approaching the GHz range, which is crucial for the modern generation of 5G communication technologies aiming to operate at the EU 5G high band (24.25-27.5 GHz). The proposed solution is to use ferrite-based Frequency Selective Limiters (FSLs), which maintain their efficiency at high GHz frequencies, although they have only been studied at the macroscale so far. In this study, we demonstrate a proof of concept of nanoscale FSLs. The devices are based on spin-wave transmission affected by four-magnon scattering phenomena in a 97-nm-thin Yttrium Iron Garnet (YIG) film. Spin waves were excited and detected using coplanar waveguide (CPW) transducers of the smallest feature size of 250 nm. The FSLs are tested in the frequency range up to 25 GHz, and the key parameters are extracted (power threshold, power limiting level, insertion losses, bandwidth) for different spin-wave modes and transducer lengths. An analytical theory has been formulated to describe the fundamental physical processes, and a numerical model has been developed to quantitatively describe the insertion losses and power characteristics of the FSLs. Additionally, the perspective of the spin-wave devices is discussed, including the possibility of simultaneously integrating three devices into one: a frequency-selective limiter, an RF filter, and a delay line, allowing for more efficient use of space and energy.

cond-mat.other

The 2026 Skyrmionics Roadmap

Magnetic skyrmions and related topological spin textures have emerged as a central topic in condensed-matter physics, combining fundamental significance with potential for transformative applications in spintronics, magnonics, and beyond. Over the past decade, advances in material platforms, imaging techniques, theoretical modeling, and device concepts have established skyrmionics as a rapidly expanding field. At the same time, challenges remain in stabilizing, controlling, and integrating such textures into functional architectures, while novel phenomena such as antiskyrmions, higher-order skyrmions, hopfions, and antiferromagnetic textures arise. The 2026 Skyrmionics Roadmap represents a collective effort of many authors, providing a comprehensive perspective on the current state-of-the-art and the outlook for the coming years. In 33 focused sections, each co-authored by two researchers, we chart progress in theory and modeling, material systems, skyrmion dynamics, and skyrmion technologies. By offering a consolidated vision, this Roadmap aims to guide both fundamental research and application-driven efforts, accelerating the transition of skyrmionics from conceptual breakthroughs toward practical technologies.

cond-mat.mes-hall

Magnetization reversal mechanism of double-helix nanowires probed by dark-field magneto-optical Kerr effect

Double-helix (DH) nanowires provide a platform to study the influence of geometric chirality on spin chirality. Their three-dimensional (3D) helical architecture and tunable inter-strand coupling enable control of spin chirality, including the stabilization of topological 3D magnetic states such as helical domains and domain walls, topological stray fields, and extended helical vortex/skyrmion tubes. So far, the study of these and other 3D nanostructures is usually confined to a limited number of magnetic microscopy experiments in large facilities. Here, we investigate the reversal mechanism of a single DH nanowire using Dark-Field magneto-optical Kerr effect (DF-MOKE) magnetometry under external 3D magnetic fields. By analyzing the angular dependence of the DF-MOKE signal, we fit the reversal process using established models for domain-wall nucleation and propagation, finding a characteristic behavior similar to that reported for cylindrical nanowires. Micromagnetic simulations indicate that the reversal process goes through nucleation of the helical vortex tube in a curling manner while ptychographic X-ray magnetic circular dichroism data reveal that this helical vortex tube state forms through a mixed nucleation-propagation process. These observations provide a consistent microscopic picture of reversal mediated by a helical vortex tube extending along the nanowire. Our work provides a comprehensive characterization of magnetization reversal in DH nanowires and demonstrates that DF-MOKE magnetometry is effective for probing reversal mechanisms in single 3D nanostructures. This lab-based approach expands the range of accessible experiments beyond large-scale facilities, enabling extensive exploration of the rich spin states supported by 3D nano-geometries.

cond-mat.mes-hall

Nucleation of magnetic skyrmions on curvilinear surfaces using local magnetic fields

Magnetic skyrmions stabilized by interfacial Dzyaloshinskii-Moriya interactions (DMI) are promising candidates for applications in memory, logic, and neuromorphic computing. Beyond planar films, theoretical studies predict that curvature can influence skyrmion stability by introducing effective chiral interactions. Here, we investigate skyrmion formation on self-assembled polystyrene particles coated with Pt/Co/Ta multilayers by magnetron sputtering. Vibrating sample magnetometry reveals clear differences in the magnetic reversal behavior of the curvilinear film compared to that of the planar counterpart. Using non-invasive imaging methods such as scanning transmission X-ray microscopy and high-sensitivity in-vacuum magnetic force microscopy (MFM) with low moment magnetic tipcs, we observe a maze domain pattern for the planar films while the curvilinear film reveals three-dimensional spiraling stripe states. By employing a conventional MFM operating under ambient conditions requiring a tip with a higher magnetic moment, we demonstrate that these stripe states can rupture into metastable skyrmions located at the top of the spherical particles by applying consecutive scans. Our results demonstrate that curvilinear films offer an accessible platform for stabilizing single skyrmions using local magnetic field stimuli, opening pathways to study the interplay between interfacial and curvature-induced DMIs and enabling controlled skyrmion writing on three-dimensional magnetic architectures.

cond-mat.mes-hall

jaxFMM: An Adaptive, GPU-Parallel Implementation of the Fast Multipole Method in JAX

We introduce jaxFMM, an open-source, adaptive, highly parallel point-charge Fast Multipole Method implementation for the Laplace kernel written in JAX. It is based on a non-uniform refinement strategy with on-the-fly rotation-based transforms tailored around JAX's just-in-time compiler, which results in extremely concise and simple code. Benchmarks show that the algorithm performs well at moderate accuracies, even for highly non-uniform charge distributions. JaxFMM already massively speeds up stray-field computations in micromagnetics and with JAX features like autodiff, novel applications such as inverse-design problems and machine-learning tasks can be tackled with ease in the future.

physics.comp-ph

Interlinking helical spin textures in nanopatterned chiral magnets

Nanoscale topologically non-trivial magnetization configurations generate significant interest due to both the fundamental properties of their knotted structures and their potential applications in ultra-efficient computing devices. While such textures have been widely studied in two dimensions, three-dimensional (3D) systems can yield more complex configurations, resulting in richer topologies and dynamic behaviors. However, reliably nucleating these 3D textures has proven challenging, and so far, 3D configurations such as vortex rings and hopfions can often only be observed forming spontaneously in relatively uncontrolled manners. Here, we demonstrate that through the 3D nanopatterning of chiral single crystal helimagnets into nano-tori, the controlled formation of a magnetic double helix can be achieved. This surface-localized topological state is stabilized by the interplay of intrinsic exchange interactions of the single crystal with the extrinsic emergent effects of the patterned geometry. These double helices host magnetic defects akin to supercoiling in circular DNA and climbing vines. We expect this study to serve as a foundation for future research combining single crystal systems with 3D nanopatterning, offering a new degree of control over emergent phenomena in nanoscale magnets and wider quantum material systems.

cond-mat.mes-hall

k-Selective Electrical-to-Magnon Transduction with Realistic Field-distributed Nanoantennas

The excitation and detection of propagating spin waves with lithographed nanoantennas underpin both classical magnonic circuits and emerging quantum technologies. Here, we establish a framework for all-electrical propagating spin-wave spectroscopy (AEPSWS) that links realistic electromagnetic drive fields to micromagnetic dynamics. Using finite-element (FE) simulations, we compute the full vector near-field of electrical impedance-matched, tapered coplanar and stripline antennas and import this distribution into finite-difference (FD) micromagnetic solvers. This approach captures the antenna-limited wave-vector spectrum and the component-selective driving fields (perpendicular to the static magnetisation) that simplified uniform-field models cannot. From this coupling, we derive how realistic current return paths and tapering shapes, k-weighting functions, for Damon-Eshbach surface spin waves in yttrium-iron-garnet (YIG) films are, for millimetre-scale matched CPWs and linear tapers down to nanometre-scale antennas. Validation against experimental AEPSWS on a $48\,nm$ YIG film shows quantitative agreement in dispersion ridges, group velocities, and spectral peak positions, establishing that the antenna acts as a tunable k-space filter. These results provide actionable design rules for on-chip magnonic transducers, with immediate relevance for low-power operation regimes and prospective applications in quantum magnonics.

cond-mat.mes-hall

Controlling bubble and skyrmion lattice order and dynamics via stripe domain engineering in ferrimagnetic Fe/Gd multilayers

Ferrimagnetic Fe/Gd multilayers host maze-like stripe domains that transform into a disordered bubble/skyrmion lattice under out-of-plane magnetic fields at ambient temperature. Femtosecond magneto-optics distinguishes these textures via their distinct coherent breathing dynamics. Crucially, applying a brief in-plane ``set'' magnetic field to the stripe state enhances both frequency and amplitude of the bubble/skyrmion lattice breathing mode. Lorentz transmission electron microscopy, magnetic force microscopy, and micromagnetic simulations reveal that this enhancement arises from field-aligned stripes nucleating a dense, near-hexagonal bubble/skyrmion lattice upon out-of-plane field application, with strong indications for a pure skyrmion lattice. Thus, modifying the initial domain configuration by in-plane fields enables precise control of coherent magnetization dynamics on picosecond to nanosecond timescales and potentially even of topology.

cond-mat.mes-hall

Modeling Magnetoelastic Wave Interactions in Magnetic Films and Heterostructures: A finite-difference approach

The (inverse) magnetostrictive effect in ferromagnets couples the magnetic properties to the mechanical stress, allowing for an interaction between the magnetic and mechanical degrees of freedom. In this work, we present a time-integration scheme for the self-consistent simulation of coupled magnetoelastic dynamics within the framework of finite-difference micromagnetism. The proposed implementation extends the Landau-Lifshitz-Gilbert equation by a strain-induced effective field and concurrently solves the elastic equation of motion, while correctly incorporating stress and strain discontinuities at material interfaces. We then present a comprehensive set of examples, ranging from static stress configurations over material boundaries to simulations of surface acoustic wave attenuation in magnetically structured thin and thick films. These computational experiments both validate the implementation and underscore the importance of properly handling jump and boundary conditions in magnon-phonon interaction studies.

physics.comp-ph

Exchange spin-wave propagation in Ga:YIG nanowaveguides

Spin-wave-based computing has emerged as a promising approach to overcome the fundamental limitations of CMOS technologies. However, the increasing demand for device miniaturization down to a 100 nm scale presents significant challenges for long-distance spin-wave transport. Gallium-substituted yttrium iron garnet (Ga:YIG) offers a potential solution to these challenges due to its unique magnetic properties. The reduced saturation magnetization in Ga:YIG enables efficient excitation of exchange-dominated spin waves, which exhibit enhanced transport characteristics compared to dipolar-dominated modes in conventional materials. Here, we present the first comprehensive study combining experimental, analytical, and numerical investigations of spin-wave propagation in Ga:YIG waveguides down to 145 nm width and 73 nm thickness. Using micro-focused Brillouin light scattering spectroscopy, TetraX simulations, and analytical dispersion calculations, we demonstrate that Ga:YIG waveguides support spin waves with significantly higher group velocities up to 600 m/s. This value remains constant for structures with different widths, leading to longer spin-wave propagation lengths in nanowaveguides compared to non-substituted YIG. These results reveal that gallium substitution provides access to faster and longer-lived spin waves, opening new possibilities for implementing this material in nanoscale magnonic devices.

cond-mat.other

Magnetically Programmable Surface Acoustic Wave Filters: Device Concept and Predictive Modeling

Filtering surface acoustic wave (SAW) signals of specified frequencies depending on the strength of an external magnetic field in a magnetostrictive material has garnered significant interest due to its potential scientific and industrial applications. Here, we propose a device that achieves selective SAW attenuation by instead programming its internal magnetic state. To this end, we perform micromagnetic simulations for the magnetoelastic interaction of the Rayleigh SAW mode with spin waves (SWs) in exchange-decoupled Co/Ni islets on a piezoelectric LiTaO$_3$ substrate. Due to the islets exhibiting perpendicular magnetic anisotropy, the stray-field interaction between them leads to a shift in the SW dispersion depending on the magnetic alignment of neighboring islets. This significantly changes the efficiency of the magnetoelastic interaction at specified frequencies. We predict changes in SAW transmission of 52.0 dB/mm at 3.8 GHz depending on the state of the device. For the efficient simulation of the device, we extend a prior energy conservation argument based on analytical solutions of the SW to finite-difference numerical calculations, enabling the modeling of arbitrary magnetization patterns like the proposed islet-based design.

cond-mat.mes-hall

SOT Enabled 3D Magnetic Field Sensor with Low Offset and High Sensitivity

In this work we demonstrate a spin-orbit torque (SOT) magnetic field sensor, designed as a Ta/CoFeB/MgO structure, with high sensitivity and capable of active offset compensation in all three spatial directions. This is described and verified in both experiment and simulation. The measurements of magnetic fields showed an offset of 36, 50, and 37$\mathrm{\mu T}$ for x-, y-, and z-fields. Furthermore, the sensitivities of these measurements had values of 590, 580, and 490$\mathrm{V\,A^{-1}\,T^{-1}}$ in the x-, y-, and z-direction. In addition, the robustness to bias fields is demonstrated via experiments and single spin simulations by applying bias fields in y-direction. Cross sensitivities were further analyzed via single spin simulations performing a parameter sweep of different bias fields in the y- and z-direction up to $\pm$1mT. Finally, the extraction of the SOT parameters $\eta_\mathrm{DL}$ and $\eta_\mathrm{FL}$ is shown via optimization of a single-spin curve to the experimental measurements.

cond-mat.mes-hall

Reconfigurable three dimensional magnetic nanoarchitectures

Three-dimensional (3D) nanomagnetism is a rapidly developing field within magnetic materials research, where exploiting the third dimension unlocks opportunities for innovative applications in areas such as sensing, data storage, and neuromorphic computing. Among various fabrication techniques, focused electron beam-induced deposition (FEBID) offers high flexibility in creating complex 3D nanostructures with sub-100 nm resolution. A key challenge in the development of 3D nanomagnets is the ability to locally control the magnetic configuration, which is essential to achieve desired functionalities. In this work, the magnetization reversal mechanism of a three-dimensional nanoarchitecture fabricated using focused electron beam-induced deposition is investigated by combining direct observation via scanning transmission X-ray microscopy with finite element micromagnetic simulations. In particular, our investigation shows that the magnetization of the components of a three-dimensional Co3 Fe tetrapod can be reversed individually and sequentially. Finally, it is demonstrated that complete control and reconfigurability of the system can be achieved by tuning the direction of the applied magnetic field.

cond-mat.mes-hall

Efficient solution strategy to couple micromagnetic simulations with ballistic transport in magnetic tunnel junctions

We present a computationally efficient strategy that allows to simulate magnetization switching driven by spin-transfer torque in magnetic tunnel junctions within a micromagnetic model coupled with a matrix-based non-equilibrium Green's function algorithm. Exemplary simulation for a realistic set of parameters are carried out and show switching times below 4 ns for voltages above 300 mV or around 2*10^{10} A m^{-2} for the P to AP (parallel to anti-parallel) direction. For AP to P switching, a trend-reversal in the switching time is seen i.e. the time for magnetization reversal first decreases with increasing bias voltage but then starts to rise again.

physics.comp-ph