arXiv subjects

Paweł Gruszecki

Publications and source records attributed to Paweł Gruszecki.

10 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.

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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.

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arXiv2025

Perpendicular magnetic anisotropy in thin films enables extraordinary spin-wave phenomena: anti-Larmor precession, negative reflection and refraction, multi-reflection and multi-refraction

We present a theoretical and numerical investigation of the role of perpendicular magnetic anisotropy (PMA) in shaping spin-wave (SW) dynamics under low magnetic fields in thin and ultrathin magnetic films. PMA introduces an in-plane torque that counteracts exchange, dipolar, and Zeeman contributions, fundamentally modifying SW dispersion and inducing a local minimum that, under specific conditions, becomes the lowest frequency across all geometric configurations. This results in a sombrero-shaped dispersion in ultrathin films and a cowboy-hat-like shape in thicker films, where dipolar interactions dominate. Using isofrequency contour (IFC) analysis, we demonstrate that these PMA-induced dispersion shapes enable nontrivial wave phenomena unprecedented in uniform media: bireflection and negative reflection in ultrathin films, and trireflection in thicker films--where a single incident beam splits into three reflected components, two with negative angles. Most remarkably, we predict and demonstrate tri-refraction, where one incident beam generates three refracted beams with two exhibiting negative refraction angles. We further show anti-Larmor precession of magnetization near the dispersion minimum in thicker films, arising from the interplay between PMA-induced and dipolar torques. Systematic simulations across diverse material systems--metallic films, ferrimagnetic garnets, hybrid structures, and multilayers--confirm the universal nature of these phenomena in any PMA system supporting stripe domain transitions. These results open new opportunities to explore wave phenomena beyond magnonics.

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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.

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arXiv2024

Goos-Hänchen shift of inelastically scattered spin-wave beams and cascade nonlinear excitation of spin-wave leaky modes

We show, by means of micromagnetic simulations, inelastic scattering of spin-wave beams on edge-localized spin waves modes. The outcome of the investigated inelastic scattering is creation of new spin-waves beams of frequencies shifted by the edge mode frequencies. We report that inelastically scattered spin-wave beams in both stimulated splitting and confluence processes not only change their direction of propagation, but also undergo lateral shifts along the interface, analogous to the Goos-Hänchen effect. We report that the lateral shifts of inelastically scattered beams can be much larger than the classical Goos-Hänchen shifts for reflected spin waves, taking both positive and negative values. In addition, we report the cascade nonlinear excitation of spin-wave leaky modes accompanied by a substantial increase in the value of the lateral shift of the inelastically scattered spin-wave beam in the confluence process. Our results are an important contribution to the understanding of the nonlinear nature of spin waves, which is crucial for spin wave applications.

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arXiv2023

Exciting high-frequency short-wavelength spin waves using high harmonics of a magnonic cavity mode

Confined spin-wave modes are a promising object for studying nonlinear effects and future quantum technologies. Here, using micromagnetic simulations, we use a microwave magnetic field from a coplanar waveguide (CPW) to pump a standing spin-wave confined in the cavity of magnonic crystal. We find that the frequency of the fundamental cavity mode is equal to the ferromagnetic resonance frequency of the plane film and overlaps with the magnonic bandgap, allowing high magnetic field tunability. Multi-frequency harmonics of the cavity mode are generated once the microwave amplitude surpasses a certain threshold. Specifically, the second and third harmonics at 0.5 T equate to 48.6 and 72.9 GHz with wavelengths of 44 and 22 nm respectively, which propagate into the crystal. This effect reaches saturation when the CPW covers the entire cavity, making the system feasible for realization. These processes show potential for the advancement of magnonics at high-frequencies and very short-wavelengths.

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arXiv2023

A modal approach to modelling spin wave scattering

Efficient numerical methods are required for the design of optimised devices. In magnonics, the primary computational tool is micromagnetic simulations, which solve the Landau-Lifshitz equation discretised in time and space. However, their computational cost is high, and the complexity of their output hinders insight into the physics of the simulated system, especially in the case of multimode propagating wave-based devices. We propose a finite-element modal method allowing an efficient solution of the scattering problem for dipole-exchange spin waves propagating perpendicularly to the magnetisation direction. The method gives direct access to the scattering matrix of the whole system and its components. We extend the formula for the power carried by a magnetostatic mode in the Damon-Eshbach configuration to the case with exchange, allowing the scattering coefficients to be normalised to represent the fraction of the input power transferred to each output channel. We apply the method to the analysis of spin-wave scattering on a basic functional block of magnonic circuits, consisting of a resonator dynamically coupled to a thin film. The results and the method are validated by comparison with micromagnetic simulations.

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arXiv2021

Control of the phase of reflected spin-waves from magnonic Gires-Tournois interferometer of subwavelength width

The phase is one of the fundamental properties of a wave that allows to control interference effects and can be used to efficiently encode information. We examine numerically a magnonic resonator of the Gires-Tournois interferometer type, which enables the control of the phase of spin waves reflected from the edges of the ferromagnetic film. The considered interferometer consists of a Py thin film and a thin, narrow Py stripe placed above its edge, both coupled magnetostatically. We show that the resonances and the phase of the reflected spin waves are sensitive for a variation of the geometrical parameters of this bi-layerd part of the system. The high sensitivity to film, stripe, and non-magnetic spacer thicknesses, offers a prospect for developing magnonic metasurfaces and sensors.

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arXiv2020

Resonant subwavelength control of the phase of spin waves reflected from a ferromagnetic film edge

Using frequency-domain finite element calculations cross-checked with micromagnetic simulations, we demonstrate that the phase of spin waves reflected from an interface between a permalloy film and a bilayer can be controlled by changing dimensions of the bilayer. Treating the bilayer formed by the permalloy film and a ferromagnetic stripe as a segment of a multi-mode waveguide, we show that spin-wave Fabry-Perot resonances of one of its modes are responsible for the high sensitivity of the phase of reflected waves to stripe width and the stripe-film separation. Thus, the system is a unique realization of a fully magnonic Gires-Tournois interferometer based on a two-modes resonator, which can be treated as a magnonic counterpart of a metasurface, since it enables manipulation of the phase of spin waves at subwavelength distances. Knowledge gained from these calculations might be used to design magnonic devices such as flat lenses or magnetic particle detectors.

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arXiv2019

Real space observation of magnon interaction with driven space-time crystals

The concept of Space-Time Crystals (STC), i.e. translational symmetry breaking in time and space, was recently proposed and experimentally demonstrated for quantum systems. Here, we transfer this concept to magnons and experimentally demonstrate a driven STC at room temperature. The STC is realized by strong homogeneous micro-wave pumping of a micron-sized permalloy (Py) stripe and is directly imaged by Scanning Transmission X-ray Microscopy (STXM). For a fundamental understanding of the formation of the STC, micromagnetic simulations are carefully adapted to model the experimental findings. Beyond the mere generation of a STC, we observe the formation of a magnonic band structure due to back folding of modes at the STC's Brillouin zone boundaries. We show interactions of magnons with the STC that appear as lattice scattering. This results in the generation of ultra short spin waves down to 100 nm wavelength that cannot be described by classical dispersion relations for linear spin wave excitations. We expect that room temperature STCs will be a useful tool to investigate non-linear wave physics, as they can be easily generated and manipulated to control their spatial and temporal band structure.

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