Andrii V. Chumak

Inverse design—specifying a desired functionality and letting a computational algorithm search for a structure that meets it—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 (AI) 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.

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.

Brillouin light scattering (BLS) is a key technique in studying magnonic systems, though its detection capabilities are often constrained by low signal-to-noise ratios. While nanoplasmonic systems can enhance BLS through near-field effects, we propose a novel approach for additional amplification. In this conceptual paper, we show how to actively supply energy to a surface common resonance (SCR) supported by a sparse layer of metal nanoparticles on a magnetic film. Proposed methods are designed to significantly amplify the efficiency of surface-enhanced Brillouin light scattering without increasing the intensity of the primary excitation. In the proposed scheme, the pump extends the propagation length of the SCR, leading directly to BLS amplification. We analyse the conditions for such amplification, with numerical estimates indicating a potential gain of more than an order of magnitude in the surface-wave amplitude. This gain far surpasses the modest increase achievable through passive enhancement alone. These findings outline a practical pathway to achieving BLS amplification in integrated magnonic platforms. The feasibility of the proposed approaches is discussed in light of recent experimental and theoretical advances in plasmonics, magneto-plasmonics, and magnonics.

Spin-wave-based computing has emerged as a promising approach to overcome the fundamental limitations of complementary metal-oxide-semiconductor 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 with 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 microfocused 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 with nonsubstituted YIG. These results reveal that gallium substitution provides access to faster and longer-lived spin waves, opening significant possibilities for implementing this material in nanoscale magnonic devices.

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 microseconds. Experiments performed on single-crystal yttrium iron garnet spheres cooled to 30 millikelvin 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.

Quantum magnonics leverages the quantum properties of magnons to advance nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), valued for its exceptionally low magnetic damping, is typically grown as thin films on gadolinium gallium garnet (GGG) for lattice matching. However, paramagnetic GGG introduces additional damping at low temperatures due to substrate magnetization, limiting quantum applications. Here, we study magnetic damping in a 150 nm-thick YIG film grown on yttrium scandium gallium aluminum garnet (YSGAG), a newly developed diamagnetic alternative to GGG. Ferromagnetic resonance spectroscopy down to 30 mK reveals that YIG/YSGAG maintains low damping from room temperature to millikelvin temperatures, with a room-temperature Gilbert damping of 4.29 × 10 ⁻⁵ , comparable to state-of-the-art YIG/GGG films and bulk YIG. Crucially, no low-temperature damping increase is observed. By eliminating paramagnetic substrate-induced dissipation, YSGAG enables consistently low damping in YIG films across the entire temperature range, establishing it as an ideal substrate for quantum magnonics and paving the way for spin-wave-based quantum technologies.

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 particularly 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 ∼18 μs for dipolar-exchange magnons at millikelvin temperatures. However, thin YIG films on gadolinium gallium garnet 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, overcome these limitations and preserve low magnetic damping down to millikelvin temperatures. These advances provide a practical pathway toward ultra-long-living magnons in thin films, enabling scalable quantum magnonics with coherent transport, strong magnon–photon and magnon–qubit coupling, and integrated quantum networks.

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.

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 loss, 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.