arXiv subjects

Maciej Krawczyk

Publications and source records attributed to Maciej Krawczyk.

At least 19 recordsLinked to original sources

arXiv2026

Spin-Wave Phase Shifter Controlled by a Domain Wall Racetrack

We propose a spin-wave phase shifter controlled using a domain-wall racetrack. The concept is demonstrated using micromagnetic simulations of a Permalloy domain-wall racetrack placed above a YIG film. The stray field from pinned domain walls modifies the internal magnetic field in the YIG region under the racetrack. This leads to a local change of the spin-wave wavelength and thereby enables control of the phase accumulated by Damon-Eshbach spin waves propagating through the region. Moving domain walls on the racetrack, the same physical structure can provide phase shifts of up to +/-90 degrees, without changing the waveguide geometry. A model based on the semiclassical approximation confirms that the phase shift is dominated by the domain-wall-induced stray field. These results suggest a route toward a compact programmable spin-wave phase shifter for interference-based magnonic circuits for information processing. Moreover, the demonstrated magnonic device integration with a magnetic domain-wall racetrack can lead to its application in in-memory computing.

cond-mat.mes-hall↗

arXiv2026

Attached Split Ring Resonator Cavity for Magnon Photon Coupling

We present a chip scale planar cavity platform based on an attached split ring resonator (ASRR) integrated with yttrium iron garnet (YIG) structures to achieve strong magnon photon coupling in a compact hybrid system. The ASRR geometry was numerically optimized by tuning inter ring spacing, gap width, substrate thickness, and permittivity, resulting in a quality factor of Q = 190 at 5.48 GHz, enabling strong microwave magnetic field confinement and reduced radiative losses. The optimized cavity was coupled to YIG elements of three geometries: full ring, half ring, and disk. Full electromagnetic simulations show that the full ring geometry exhibits balanced performance with coupling strength 115 MHz and cooperativity 13.10, while the half ring shows a comparable coupling strength of 108 MHz and slightly higher cooperativity 13.50, despite edge induced demagnetizing effects. In contrast, the disk geometry couples at lower bias magnetic fields and achieves the strongest interaction (135 MHz, 25.30), enabled by improved microwave magnetic field overlap. These results demonstrate that geometry, rather than magnetic volume alone, is a key design parameter for tailoring magnon photon coupling, providing a practical framework for lithography compatible, on chip hybrid magnonic and quantum devices.

cond-mat.mtrl-sci↗

arXiv2026

Spin-wave bandgap engineering via mode hybridization in dipolar-coupled YIG film/CoFeB nanodisk magnonic crystals

We investigate spin-wave transport in hybrid two-dimensional magnonic crystals comprising a low-damping yttrium iron garnet (YIG) film coupled to a periodic array of CoFeB nanodisks. Using propagating spin-wave spectroscopy, super-Nyquist magneto-optical Kerr effect microscopy, and micromagnetic simulations, we demonstrate the formation of pronounced and tunable bandgaps that do not originate from conventional Bragg scattering. Instead, these gaps arise from hybridization between the fundamental magnonic-crystal mode and in-plane transverse standing modes induced by the periodic nanodisk array. The spectral position and width of these gaps are controlled by geometric parameters and by the magnetic state of the nanodisks, including their vortex configuration, which governs both static and dynamic dipolar coupling. For larger lattice periods, additional gaps emerge through hybridization with modes quantized both transverse and parallel to the spin-wave propagation direction, reflecting dispersion folding in two dimensions. Our results establish mode hybridization as a versatile mechanism for engineering spin-wave band structures beyond the constraints of Bragg scattering and provide a pathway toward reconfigurable magnonic devices based on dipolar-coupled hybrid architectures.

cond-mat.mes-hall↗

arXiv2026

Controlling the Spin-Wave Nonreciprocity of a Crescent-Shaped Nanowire via Curvature and Magnetic Field

Recent studies on spin-wave propagation in ferromagnetic waveguides has highlighted the role of nonreciprocity resulting from the chiral nature of dipolar interactions in curved elements. However, the impact of spin-wave mode type on nonreciprocity remains unexplored. Using micromagnetic simulations supported by analytical modeling, we systematically analyzed the propagation of edge, fundamental, and width-quantized spin-wave modes in a ferromagnetic nanowire with a crescent-shaped cross-section. Our results show that the strength and sign of nonreciprocity depend on the mode type, as well as on the curvature magnitude of the nanowire's top and bottom surfaces and the strength of the external magnetic field. Interestingly, changing the mode type, for instance induced by altering the curvature or magnetic field, result in a significant change in the dispersion relation asymmetry. This effect underscores the important role of spin-wave profiles in nonreciprocity, deepens our fundamental understanding of spin-wave dynamics in curved geometries, and paves the way for designing magnonic waveguides with tailored properties.

cond-mat.mes-hall↗

arXiv2026

Anisotropic second-harmonic generation in superconducting nanostructures

Circuits based on superconducting nanostructures are among the most promising platforms for quantum computing. Understanding how device geometry governs nonlinear electrodynamics is crucial for implementing superconducting quantum technologies. However, to date, research has largely been limited to superconducting nanostructures with collinearly aligned static and dynamic applied magnetic fields. Here, we analyze the dynamics of Meissner currents and Abrikosov vortices in a superconducting nanocube exposed to combined static and microwave magnetic fields, extending the analysis to a more general excitation geometry. We demonstrate that, in a noncollinear configuration,the magnetization component parallel to the static field develops a dominant second-harmonic response under the microwave driving. This effect is strongly enhanced when Meissner currents saturate at static fields just below the thresholds for successive vortex nucleation. By numerically solving the time-dependent Ginzburg-Landau equations, we show that the response originates from Meissner-current saturation combined with the nonlinear oscillations of normal-phase indentations, yielding an anisotropic second-harmonic signal that is directionally separated from, and not overshadowed by, the first-harmonic component of the dynamic magnetization. These findings are relevant for superconducting devices that require controllable high-frequency nonlinearity.

cond-mat.supr-con↗

arXiv2025

Hybrid structure with a ferromagnetic film and an array of magnetic molecules for deep-nanoscale reprogrammable magnonics

Miniaturization is an essential element in the development of information processing technologies and is also one of the main determinants of the usability of the tested artificial neural networks. It is also a key element and one of the main challenges in the development of magnonic neuromorphic systems. In this work, we propose a new platform for the development of these new spin-wave-based technologies. Using micromagnetic simulations, we demonstrate that magnetic molecules regularly arranged on the surface of a thin ferromagnetic layer enable resonant coupling of propagating spin waves with the dynamics of the molecules' magnetic moments, opening a gap in the transmission spectrum up to 150 MHz. The gap, its width, and frequency can be controlled by an external magnetic field or the arrangement of molecules on the ferromagnetic surface. Furthermore, the antiferromagnetic arrangement of the magnetic moments of molecules or clusters of molecules allows for control of the gap's position and width. Thus, the proposed hybrid structure offers reprogrammability and miniaturization down to the deep nanoscale, operating frequencies in the range of several GHz, key properties for the implementation of artificial neural networks.

cond-mat.mes-hall↗

arXiv2025

Unveiling Micrometer-Range Spin-Wave Transport in Artificial Spin Ice

Artificial spin ice (ASI) systems exhibit fascinating phenomena, such as frustration and the formation of magnetic monopole states, and Dirac strings. However, exploring the wave phenomena in these systems is elusive due to the weak dipolar coupling that governs their interactions. In this study, we demonstrate coherent spin-wave propagation in an hybrid ASI system, which is based on a multilayered ferromagnetic thin film with perpendicular magnetic anisotropy and in-plane magnetized nanoelements embedded within it. We show that this system enables spin-wave transmission over a one-micrometer distance via exchange-mediated coupling between subsystems and evanescent spin-wave tunneling through the out-of-plane magnetized parts. This system overcomes the limitations of purely dipolar interactions in standard ASIs while preserving their fundamental properties. Thus, it provides a platform for studying spin-wave phenomena in frustrated ASI systems and paves the way for exploiting them in analog signal processing with spin waves.

cond-mat.mes-hall↗

arXiv2025

Efficient Generation of Second-Harmonic Propagating Spin Waves in a Thin, Out-of-Plane-Magnetized Ferromagnetic Film

Spin waves are attractive information carriers owing to their gigahertz-to-terahertz frequencies, nanometric wavelengths, and negligible Joule heating. Yet the efficient excitation of short-wavelength, high-frequency spin waves and the exploitation of nonlinear effects remain challenging. We propose a hybrid ferromagnetic nanostructure composed of a small, in-plane-magnetized rim (a magnonic nanocavity) exchange-coupled to an out-of-plane-magnetized region. Micromagnetic simulations show that a spatially uniform out-of-plane microwave field excites the rim's fundamental mode; its second harmonic is then coherently and efficiently launched into the second region of the structure, yielding propagating spin waves. The process can be realized in strip or disk geometries, providing excitation of plane-wave or radial spin waves, respectively. The conversion efficiency grows nonlinearly with the pump amplitude and can be further improved when the frequency of a higher-order standing wave in the nanocavity matches the second-harmonic frequency. The emission frequency is tunable via the bias magnetic field or the width of the nanocavity, suggesting a compact route toward on-chip, short-wavelength, high-frequency spin-wave sources for artificial neural networks.

cond-mat.mes-hall↗

arXiv2025

Three-magnon scattering of spin wave on edge-localized mode in thin ferromagnetic film

Three-wave scattering is a fascinating phenomenon with many applications in various technologies. Reducing the system symmetry greatly affects three-wave scattering, which, in this case, goes beyond the simple momentum conservation law. In this study, we examine three-magnon scattering at the edge of a thin ferromagnetic film, when a bulk spin wave interacts with an edge-localized propagating spin-wave upon the reflection. This creates new bulk spin waves at mixed frequencies by means of three-magnon confluence or stimulated splitting processes. Using our developed analytical theory, which has been confirmed by full micromagnetic simulations, we demonstrate that the amplitude of the wave generated in the stimulated splitting process is several times larger than that generated in the confluence process, primarily due to the lower group velocity. Furthermore, intensity of inelastically scattered waves exhibit a pronounced dependence on the incidence angle and frequency of the edge spin wave that goes beyond existing qualitative models. We show that the observed behaviors can only be explained by taking into account, that the scattered waves are created by several elementary three-magnon processes involving the incident and reflected waves. The complex nature of the scattered wave creation results in a strong sensitivity of its amplitude to the phase accumulation of spin waves upon reflection.

cond-mat.mes-hall↗

arXiv2025

Coherent Spin Waves in Curved Ferromagnetic Nanocaps of a 3D-printed Magnonic Crystal

Coherent magnon modes in a truly three-dimensional (3D) magnonic crystal have not yet been investigated. This scientific gap exists despite the numerous theoretical predictions about miniband formation and edge modes with topological protection. Such properties are key to advance nanomagnonics for ultrafast data processing. In this work, we use a scalable nanotechnology and integrate a 3D magnonic crystal to an on-chip microresonator. It was fabricated by two-photon lithography of a 3D woodpile structure and atomic layer deposition of 30-nm-thick nickel. Operated near 14 and 24~GHz, the microresonator output revealed numerous coherent magnons with distinct angular dependencies reflecting the underlying face-centred cubic lattice. Micromagnetic simulations show that the edge modes are localised in curved nanocaps and robust against changes in field orientation. Along an edge, they exhibit an unexpected phase evolution. Our findings advance functional microwave circuits with 3D magnonic crystals and fuel their visionary prospects of edge-dominated magnon modes.

cond-mat.mes-hall↗

arXiv2025

Influence of photon-magnon coupling to enhance spin-wave excitation

One of the main challenges in magnonics is the efficiency of the conversion of microwave signals into spin waves. This efficiency is low due to the significant mismatch between microwave and spin wave wavelengths in the GHz range $10^{-2}$ m and $10^{-8}$ m, respectively, leading to high energy consumption in magnonic circuits. To address this issue, we propose an approach based on a planar inverse split-ring resonator (ISRR) loaded with a nanometer-thick Py film and exploiting the photon-magnon coupling effect. Our numerical studies show that the ISRR-based antenna achieves more than a fourfold improvement in conversion efficiency compared to a conventional single microstrip transmission line at frequencies and bias magnetic fields around the anti-crossing frequency gap. This has been demonstrated in the weak photon-magnon coupling regime for the nanometer-thin permalloy film with micrometer lateral dimensions. Further optimization of the ISRR can help to achieve the strong coupling regime, making the system potentially useful for quantum technology. Our compact and efficient antenna design offers a significant advantage over standard microstrip lines, paving the way for scalable and powerful magnonic circuits for microwave signal processing.

cond-mat.mes-hall↗

arXiv2025

Beyond fixed-size skyrmions in nanodots: switchable multistability with ferromagnetic ring

We demonstrate a novel approach to control and stabilize magnetic skyrmions in ultrathin multilayer nanostructures through spatially engineered magnetostatic fields generated by ferromagnetic nanorings. Using analytical modeling and micromagnetic simulations, we show that the stray fields from a Co/Pd ferromagnetic ring with out-of-plane magnetic anisotropy significantly enhance Néel-type skyrmion stability in an Ir/Co/Pt nanodot, even without Dzyaloshinskii-Moriya interaction. Most notably, we observe a multistability phenomenon, where skyrmions can be stabilized at two or more distinct equilibrium diameters depending on the ring's magnetization orientation. These stable states exhibit energy barriers substantially exceeding thermal fluctuations at room temperature, suggesting practical applications for robust multibit memory storage. By tuning geometric parameters of the ferromagnetic ring, we demonstrate precise control over skyrmion size and stability, opening pathways for advanced spintronic nanodevices.

cond-mat.mes-hall↗

arXiv2025

Optical excitation and detection of high-frequency Sezawa modes in Si/SiO2 system decorated with Ni80Fe20 nanodot arrays

Surface acoustic waves have emerged as one of the potential candidates for the development of next-generation wave-based information and computing technologies. For practical devices, it is essential to develop the excitation techniques for different types of surface acoustic waves, especially at higher microwave frequencies, and to tailor their frequency versus wave vector characteristics. We show that this can be done by using ultrashort laser pulses incident on the surface of a multilayer decorated with a periodic array of metallic nanodots. Specifically, we study surface acoustic waves in the dielectric substrate Si/SiO2 decorated with a square lattice of thin Ni80Fe20 (Py) dots. Using a femtosecond laser-based optical pump-probe measurement, we detect a number of high-frequency phononic modes. By performing finite element simulations, we identify them as Sezawa modes from the second and third Brillouin zone in addition to the modes confined within the Py dots. The frequency of the Sezawa modes strongly depends on the period of the Py dots and varies in the range between 5 to 15 GHz. Both types of waves cover the same frequency range for Py dots with period less than 400 nm, providing a promising system for magnetoelastic studies.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic field-controlled nanoscale spin-wave vertical directional coupler

The directional coupler is a fundamental element of wave-based circuits. The state of the art for the spin-wave directional couplers consists mostly of macroscopic waveguides or two-dimensional planar systems. In this Letter, we present the design of the nanoscale spin-wave vertical directional coupler with a very high efficiency exceeding 99.5%. We demonstrate that the operation of the coupler can be controlled by the magnitude of the external magnetic field. Moreover, it can perform multiplexing and demultiplexing of the spin-wave signal. Such a device ought to become an essential element of the three-dimensional magnonic circuits.

cond-mat.mes-hall↗

arXiv2024

Enhancement of dynamical coupling in artificial spin-ice systems by incorporating perpendicularly magnetized ferromagnetic matrix

Artificial spin-ice systems, consisting of arrays of interacting ferromagnetic nanoelements, offer a versatile platform for reconfigurable magnonics with potential in GHz logic and neuromorphic computing. However, weak dipolar coupling between nanoelements severely limits their functionality. We numerically demonstrate a rich spin-wave spectrum in a square spin-ice structure immersed in a perpendicularly magnetized ferromagnetic matrix, which is different from a single spin-ice system. We observe a strong magnon-magnon coupling between the bulk second-order mode of the nanoelements and the fundamental mode of the matrix, supported by a pronounced anticrossing frequency gap. We show that, in addition to the dipolar coupling, exchange interactions at the nanoelement-matrix interface play a crucial role in this hybridization. Furthermore, the strength of the coupling can be enhanced by almost 40% just by reconfiguring the magnetization at the vertices from low-energy to high-energy monopole states. These results open the way to exploit artificial spin-ice systems for magnonic applications, taking advantage of the strong coupling and vertex-dependent dynamics.

cond-mat.mes-hall↗

arXiv2024

Nucleation and Arrangement of Abrikosov Vortices in Hybrid Superconductor-Ferromagnetic Nanostructure

This study investigates the nucleation, dynamics, and stationary configurations of Abrikosov vortices in hybrid superconductor-ferromagnetic nanostructures exposed to inhomogeneous magnetic fields generated by a ferromagnetic nanodot. Using time-dependent Ginzburg-Landau simulations and Maxwell's equations, we observe and provide an explanation for the evolution of curved vortex structures that undergo creep-like deformation while reaching a steady state. Spatial variations in the Lorentz force, along with the interaction between geometric constraints and vortex interactions, give rise to unusual stationary vortex configurations that gradually change with increasing field strength, a behavior not seen in homogeneous magnetic fields. These findings reveal complex pinning mechanisms, providing valuable insights for the optimization and further advancement of nanoscale superconducting systems.

cond-mat.supr-con↗

arXiv2024

Spin wave frequency hysteresis in Ir/Co/Pt multilayers with Dzyaloshinskii-Moriya interaction

Results of extensive combined experimental and theoretical investigations on static and dynamic properties of Ir/Co/Pt multilayer with low uniaxial anisotropy and asymmetric Ir/Co and Co/Pt interfaces responsible for large interfacial Dzyaloshinskii-Moriya interaction (IDMI) are presented. Within longitudinal magneto-optical Kerr effect-based microscopy and magnetic force microscopy studies a complex magnetic configuration was detected: large in-plane magnetized domains of several dozen micrometers size were modulated by a weak stripe domain pattern with periods of about 100 nm. Using Brillouin Light Scattering spectrometry, the hysteresis of the Stokes and anti-Stokes peaks frequencies was observed as a function of the magnetic field. This hysteretic behavior associated with IDMI-induced asymmetry of spin waves dispersion is correlated with switching of the large macro-domains. Using micromagnetic simulations we determine field-dependent magnetization distributions and dispersion relations, proposing an explanation of the observed behavior. The investigated nanostructure can be used as non-volatile spin waves velocity switcher.

cond-mat.mtrl-sci↗

arXiv2024

Reconfigurable spin-wave platform based on interplay between nanodots and waveguide in hybrid magnonic crystal

We present a hybrid magnonic crystal composed of a chain of nanodots with strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction, positioned above a permalloy waveguide. The micromagnetic study examines two different magnetization states in the nanodots: a single-domain state and an egg-shaped skyrmion state. Due to the dipolar coupling between the dot and the waveguide, a strongly bound hybrid magnetization texture is formed in the system. Our results show complex spin-wave spectra, combining the effects of periodicity, magnetization texture, and hybridization of the propagating waves in the waveguide with the dot/skyrmion modes. The dynamics of the systems are characterized by several key features which include differences in band-gap sizes, the presence of flat bands in the skyrmion state that can form both bound and hybridized states, the latter sometimes leading to the presence of additional non-Bragg band gaps, and a broad frequency range of only waveguide-dominated modes in the single-domain state. Thus, the study shows that the proposed hybrid magnonic crystals have many distinct functionalities, highlighting their reconfigurable potential, magnon-magnon couplings, mode localization, and bound states overlapping with the propagating waves. This opens up potential applications in analog and quantum magnonics, spin-wave filtering, and the establishment of magnonic neural networks.

cond-mat.mes-hall↗