arXiv subjects

Andrii V. Chumak

Publications and source records attributed to Andrii V. Chumak.

At least 19 recordsLinked to original sources

arXiv2026

Anisotropic wavevector-dependent damping of thickness-quantized magnons

Magnon damping is a key factor governing spin-wave transport and nonlinear dynamics of multimode magnon systems. However, many descriptions rely on the assumption of an effective mode-independent parameter, which can mask wavelength-dependent relaxation processes that depend on propagation geometry and mode profile. Here, we employ high-resolution parametric-instability spectroscopy to probe thickness-quantized spin waves with wavelengths down to about a hundred nanometers in micrometer-thick yttrium iron garnet films. The instability threshold exhibits a regular sawtooth dependence on the magnetic field, arising from switching between discrete thickness modes. Comparison with dipole--exchange theory reveals anisotropic wavevector-dependent damping that increases with mode number and depends differently on the in-plane and out-of-plane wavevector components.

cond-mat.mes-hall↗

arXiv2026

Exchange-mediated directional coupling of short-wavelength spin waves

Miniaturizing magnonic circuits and increasing their processing speed require spin waves with progressively shorter wavelengths. However, conventional directional couplers rely on the dynamic dipolar interaction between spatially separated waveguides, which rapidly weakens in the exchange-dominated regime. As a result, their coupling length increases as the spin-wave wavelength decreases, limiting further device miniaturization. Here, we introduce an exchange-mediated directional coupler by replacing the nonmagnetic gap between two waveguides with a magnetically modified YIG spacer. The spacer provides a continuous exchange pathway and preserves the splitting between the symmetric and antisymmetric modes at large wavenumbers. We develop an analytical model to describe this mechanism and verify it using micromagnetic simulations. Based on this concept, we design a straight coupler without curved access waveguides, with a footprint of only 400 nm * 30 nm. For a spin-wave wavelength of approximately 100 nm, the device transfers approximately 98% of the normalized output power to the target waveguide. Its performance remains nearly unchanged even when the damping of the spacer is strongly increased. These results overcome the short-wavelength limitation of dipolar couplers and provide a route toward highly integrated magnonic circuits for information processing.

physics.app-ph↗

arXiv2026

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↗

arXiv2026

Brillouin Light Scattering Spectroscopy of Propagating Magnons at Sub-Kelvin Temperatures

Coupling light to magnetic excitations in the form of spin waves underpins both the optical study of magnetism and emerging schemes for quantum transduction, positioning the quanta of these excitations, magnons, as promising carriers for hybrid quantum networks. However, exploiting them in the quantum regime requires millikelvin temperatures to suppress thermal magnon populations, thereby confining such experiments to dilution refrigerators. There, magnons can already be excited and read out electrically, yet an optical interface required for microwave-to-optical photon conversion has been missing. Here, we demonstrate the first optical detection of coherently driven, propagating spin waves via Brillouin Light Scattering (BLS) spectroscopy inside a dilution refrigerator. By simultaneously recording the optical and electrical responses of the same spin-wave mode in a yttrium iron garnet film, we find that the BLS spectra track the electrically measured transmission across a range of applied magnetic fields. For the lowest optical power of 7.9 μW that still enabled spin-wave detection, we measured a global equilibrium sample temperature of 510 mK via a resistance thermometer, while numerical modelling of the laser-induced heating yields a maximum local temperature of 900 mK at the focal spot. This brings free-space optical access to magnons into the sub-kelvin regime, representing a milestone towards magnon-mediated quantum transduction in hybrid quantum systems.

cond-mat.other↗

arXiv2026

Integrated magnonic neural circuits based on nonlinear wave neurons

Artificial intelligence is driving intense interest in alternative computing hardware capable of neural information processing beyond conventional charge-based electronics. Among emerging approaches, wave-based computing promises highly parallel and energy-efficient operation, but scalable physical neural hardware has remained elusive because wave systems generally lack cascadable nonlinear neurons with signal regeneration and phase-robust operation. Here we demonstrate integrated magnonic neural circuits based on nonlinear threshold neurons realized in nanoscale yttrium iron garnet waveguides. The neurons perform weighted summation of multiple spin-wave inputs, while a pump-controlled nonlinear activation defines continuously tunable firing thresholds. Owing to deeply nonlinear spin-wave dynamics, the activated neurons emit self-normalized outputs whose intensities are largely independent of the input amplitudes, while nonlinear phase self-adjustment suppresses sensitivity to the relative input phases, enabling deterministic neuron-to-neuron cascading without external signal restoration. We experimentally realize programmable threshold neurons, reconfigurable weighted classification and deterministic cascading between sequential neuronal stages, and further demonstrate reconfigurable physical pattern recognition in a seven-neuron integrated magnonic circuit through experimental classification of the binary letter patterns 'HUST'. These results establish nonlinear magnons as a scalable platform for integrated neural hardware and position nonlinear wave dynamics as a general paradigm for physical neuromorphic computing.

cond-mat.mtrl-sci↗

arXiv2026

Ultrafast formation of a large dynamic magnetic soliton

Nonlinear magnetization dynamics offers a rich variety of phenomena ranging from bistability to chaos. Here, we report the ultrafast formation of a dynamic magnetic soliton in thin ferrimagnetic garnet films with perpendicular magnetic anisotropy, driven by the microwave magnetic field of a microstrip antenna. Using time-resolved Brillouin light scattering microscopy and scanning transmission X-ray microscopy, we directly track the build-up of the large-angle precession state. The observed soliton is distinct from other nonlinear magnetic excitations in two key aspects: (i) it forms inside the linear spin-wave frequency band, and (ii) it is exceptionally large, reaching tens of microns beyond the antenna. We explain the soliton formation by the self-limiting mechanism upon a positive nonlinear frequency shift and the spatial extent of the near-field of the antenna. At large distances from the drive, the soliton collapses and emits short-wavelength spin waves via almost instantaneous spatial wavenumber conversion. Time-resolved measurements further reveal a small finite delay during soliton formation, while coherent long-range oscillations appear essentially simultaneously over distances up to 40 micrometers. These results establish microwave-driven solitons as a robust nonlinear phenomenon in thin-film garnets and suggest opportunities for fast, nonlocal manipulation of magnetic states and for applications in novel computational schemes.

cond-mat.mes-hall↗

arXiv2026

Bulk-mediated reflection of chirality-protected surface spin waves

Surface spin waves of the Damon-Eshbach type exhibit intrinsically nonreciprocal transport properties with a chiral dynamical field structure that localizes counterpropagating waves at opposite film surfaces. Such chirality has been predicted to suppress direct backscattering in thin films within frequency ranges free of bulk modes. However, how chirality influences reflection in thicker three-dimensional magnetic media, where a dense spectrum of bulk excitations overlaps with surface waves, remains unclear. Here we demonstrate that, in micrometer-thick yttrium iron garnet films, reflection of the chiral Damon-Eshbach wave from the boundary of the magnetic medium is accompanied by excitation of spatially localized thickness-quantized bulk modes, whereas reciprocal backward-volume waves reflect nearly elastically. Brillouin light scattering spectroscopy, infrared thermography, and micromagnetic simulations reveal standing bulk excitations at the reflecting boundary and quantify the associated magnon energy accumulation and dissipation. These results identify bulk-mode excitations as the physical pathway enabling reversal of chirally localized surface waves in thick films, thereby defining the limits of chirality-based backscattering immunity and providing a general framework for wave transport in nonreciprocal magnetic media.

cond-mat.other↗

arXiv2026

True random number generation through stochastic magnonic bistability

True random number generators (TRNGs) underpin modern cryptography, yet existing implementations face fundamental trade-offs between speed, scalability, and entropy quality. Here, we demonstrate that stochastic switching in the bistable regime of spin-wave dynamics provides a physical entropy source for high-quality random number generation. Our magnonic random number generator (mRNG), based on a lithography-patterned microstrip on yttrium iron garnet (YIG), exploits thermal fluctuations near the nonlinear bistable regime to generate random bitstreams that pass all 15 NIST SP 800-22 statistical tests at rates with 20 Mb/s. We implement a random-bit multiplier using synchronized mRNG units and demonstrate scalability to 200-nm-wide nanoscale waveguides, establishing spin-wave bistability as a viable physical entropy source for integrated random number generation.

cond-mat.mtrl-sci↗

arXiv2026

Magnetic Materials for Quantum Magnonics

Quantum magnonics studies the quantum properties of magnons, the quanta of spin waves, and their application in quantum information processing. Progress in this field depends on identifying magnetic materials with characteristics tailored to the diverse requirements of magnonics and quantum magnonics. For single-magnon excitation, its control, hybrid coupling, and entanglement, the most critical property is the ability to support long magnon lifetimes. This perspective reviews established and emerging magnetic materials, including ferromagnetic metals, Heusler compounds, antiferromagnets, altermagnets, organic and 2D van der Waals magnets, hexaferrites, europium chalcogenides, and in particular yttrium iron garnet (YIG), highlighting their key characteristics. YIG remains the benchmark, with bulk crystals supporting sub-microsecond Kittel-mode lifetimes and ultra-pure spheres achieving $\sim18\,μ$s for dipolar-exchange magnons at millikelvin temperatures. However, thin YIG films on gadolinium gallium garnet (GGG) substrates suffer from severe lifetime reduction due to substrate-induced losses. In contrast, YIG films on a new lattice matched, diamagnetic alternative, yttrium scandium gallium/aluminum garnet (YSGAG), overcomes these limitations and preserves low magnetic damping down to millikelvin temperatures. These advances provide a practical pathway toward ultralong-living magnons in thin films, enabling scalable quantum magnonics with coherent transport, strong magnon-photon, magnon-qubit coupling, and integrated quantum networks.

cond-mat.mtrl-sci↗

arXiv2026

Quantum State Preparation of Ferromagnetic Magnons by Parametric Driving

We propose a method to prepare and certify Gaussian quantum states of the ferromagnetic resonance spin-wave modes in ferromagnets using a longitudinal drive. Contrary to quantum optics-based strategies, our approach harnesses a purely magnonic feature - the spin-wave nonlinearity - to generate magnon squeezing. This resource is used to prepare vacuum-squeezed states, as well as entangled states between modes of different magnets coupled via a microwave cavity. We propose methods to detect such states with classical methods, such as ferromagnetic resonance or local pickup coils, and quantify the required detection efficiency. We analytically solve the case of ellipsoidal yttrium iron garnet ferrimagnets, but our method applies to a vast range of shapes and sizes. Our work enables quantum magnonics experiments without single-magnon sources or detectors (qubits), thus bringing the quantum regime within reach of the wider magnonics community.

cond-mat.mes-hall↗

arXiv2026

Integrated magnonic chip using cascaded logic

The transistor transformed not only electronics but everyday life, and the integrated circuit - now simply the "chip" - made computation scalable and ubiquitous. Magnonics has long promised a parallel path to low-energy information processing by using spin waves instead of charge. Progress, however, has been limited by two fundamental obstacles: intrinsic attenuation of spin waves and the requirement for precisely normalised output intensity and input phase to ensure reliable logic operation - conditions that are difficult to maintain in large-scale circuits owing to inevitable imperfections. Here, we report an integrated magnonic circuit that overcomes both limitations through engineered nonlinearity in nanoscale yttrium iron garnet waveguides. Nonlinear self-adjustment of the spin wave phase renders logic operation insensitive to the relative phases of the inputs, while a deeply nonlinear, threshold-activated self-normalised excitation restores and standardises the output intensity. Using space-resolved micro-focused Brillouin light scattering, we demonstrate reconfigurable AND, OR and three-input majority gates and realise deterministic cascading across sequential stages, establishing a scalable on-chip logic primitive. The architecture operates with gigahertz frequencies, supports dynamic threshold control for functional reconfiguration, and is compatible with scalable integration, making it attractive for adaptive and neuromorphic computing. By resolving phase-independent operation and signal restoration at the level of device physics, this work advances magnonics from isolated proof-of-concept devices towards integrated magnonic chips that can complement advanced CMOS in energy-constrained computing tasks.

cond-mat.mtrl-sci↗

arXiv2025

Ultra-long-living magnons in the quantum limit

Solid-state platforms based on bosonic quasiparticles offer a compelling route toward on-chip quantum information technologies scalable to nanometer dimensions. Coherence time, a key figure of merit for any quantum system, is fundamentally limited by the lifetime of quasiparticles that store quantum information. For magnons - bosonic excitations of collective magnetization dynamics - it has long been reported that their lifetime does not exceed a few hundred nanoseconds, placing a stringent constraint on their use in quantum architectures. Here, we demonstrate magnon lifetimes exceeding 18 μs. Experiments performed on single-crystal yttrium iron garnet spheres cooled to 30 mK reveal relaxation times of short-wavelength magnons nearly two orders of magnitude longer than previously observed. These findings overturn the established view of magnon dissipation limits, positioning magnons as viable, long-lived information carriers for solid-state quantum computing.

cond-mat.mtrl-sci↗

arXiv2025

Unified theory of magnetization temperature dependence in ferrimagnets

Recent advancements in spintronics and fundamental physical research have brought increased attention to the rare-earth-based magnetically ordered materials. One of the important properties of these materials is the temperature dependence of the spontaneous magnetization $M(T)$. Recently, a successful framework was proposed for the theoretical description of M(T) across the entire temperature range from zero to the Curie temperature in simple cubic ferromagnets, EuO and EuS. We extend this approach to compute and analyze $M(T)$ for multi-sublattice collinear ferrimagnets such as Yttrium Iron Garnet $Y_3Fe_5 O_{12}$. We analyzed and generalized for multi-sublattice collinear ferrimagnets two well-known approximations describing $M(T)$. The first approach is the Bloch-3/2 law, which describes the suppression of $M(T)$ due to spin-wave excitation, and is valid in the low-temperature limit $T << T_c$. The second one is Weiss's mean-field approximation, which provides a reasonable description of $M(T)$ near $T_c$. Using a single tuning parameter, we combine these two approaches to describe $M(T)$ for any $0<T<T_c$. The theoretical result for $M(T)$ aligns well with our measurements and the previously available experimental data across the entire temperature range. We also demonstrate that experimental and theoretical dependences $M(T)$ follow the mean-field prediction $\sqrt{T_c - T }$ for almost all temperatures.

cond-mat.mtrl-sci↗

arXiv2025

Ultrafast propagation of magnon-polaritons

The manipulation of magnetization lies at the heart of spintronic and magnonic technologies, with the ultimate performance of such systems limited by the velocity at which magnetic excitations can propagate. Here, we demonstrate ultrafast propagation of magnon-polaritons-hybrid quasiparticles arising from the coupling between spin waves and electromagnetic fields in thin pure, bismuth-, and gallium substituted yttrium iron garnet (YIG, Bi:YIG and Ga:YIG) films. Using time- and phase-resolved Brillouin light scattering microscopy and time-resolved scanning transmission microscopy, we show that magnon-polaritons can propagate faster than 100 km/s, nearly three orders of magnitude more than conventional spin waves, and can be observed at distances exceeding 40 micrometers in 20 nm thick films. Analytical modeling based on retarded Maxwell equations and Polder tensor formalism confirms the hybridized nature of the excitations and captures the nontrivial dispersion and attenuation profiles. Notably, the magnon-polaritons maintain high initial magnetization amplitudes and long decay lengths, enabling ultrafast manipulation of the magnetization far away from the excitation source. We show, that they can move domain walls or stabilize nonlinear magnetization processes. The unprecedentedly high propagation velocities make magnon-polaritons promising candidates for high-speed information transfer in future spin-based computing architectures, potentially overcoming long-standing group delay bottlenecks in magnonic logic circuits.

physics.app-ph↗

arXiv2025

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↗

arXiv2025

YSGAG: The Ideal Substrate for YIG in Quantum Magnonics

Quantum magnonics leverages the quantum properties of magnons to advance nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), known for exceptionally long magnon lifetimes, is a cornerstone material typically grown as thin films on gadolinium gallium garnet (GGG) for lattice matching. However, paramagnetic GGG introduces detrimental damping at low temperatures due to substrate magnetization, undermining quantum applications. Here, we study magnetic damping in a 150$\,$nm-thick YIG film on a yttrium scandium gallium aluminum garnet (YSGAG) substrate, a newly developed diamagnetic alternative to GGG. Using ferromagnetic resonance spectroscopy down to 30$\,$mK, we compare YIG/YSGAG with a conventional YIG/GGG reference system. We demonstrate that the YIG/YSGAG system maintains low damping from 300$\,$K to 30$\,$mK, with $α= 4.29\times10^{-5}$ at room temperature, comparable to the best YIG/GGG films and bulk YIG, with no low-temperature upturn. The diamagnetic substrate eliminates the dissipation mechanisms that dominate on magnetized GGG, preserving low magnetic damping across the full temperature range. Consequently, YSGAG serves as an ideal substrate for YIG films in quantum magnonics and is paving the way for the development of spin-wave-based quantum technologies.

cond-mat.mes-hall↗

arXiv2025

Review on spin-wave RF applications

This review explores the development of spin-wave technology, highlighting magnonics as a promising route for radio frequency (RF) communication systems. The rollout of 5G and the upcoming 6G networks intensifies the demand for devices that can operate at higher frequencies while remaining scalable, compact, and energy-efficient - requirements that spin waves are well suited to meet. The first two sections revisit the fundamentals of magnonics, trace major milestones in spin-wave research, and summarize recent advances in materials and device design. The third section reviews RF applications studied over the past 50 years, with emphasis on key passive components, such as filters, limiters, delay lines, phase shifters, and directional couplers. The final section discusses both the advantages and the open challenges of spin-wave devices, including insertion losses, linearity, and power handling, together with the strategies to address them. By linking fundamental insights with technological needs, this review outlines a path toward practical RF platforms. Spin-wave-based devices, with their scalability, versatility, and potential for low-power operation, hold strong promise for future wireless communication, particularly in the 5G and 6G era.

physics.app-ph↗

arXiv2025

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↗