Magnon-magnon Coupling Research Articles

Strong magnon-magnon coupling and low dissipation rate in an all-magnetic-insulator heterostructure

Strong magnon-magnon coupling and low dissipation rate in an all-magnetic-insulator heterostructure

Magnon Excitation Modes in Ferromagnetic and Antiferromagnetic Systems

Magnons, recognized as the quanta of spin waves, offer a pathway for transmitting information without the need for electron motion, thus emerging as a leading candidate for the next generation of low-power electronics. Firstly, this study gives an overview by examining magnon modes possessing infinite wavelengths or zero wave numbers (known as ferromagnetic resonance) in classical ferromagnetic, antiferromagnetic, and synthetic antiferromagnetic systems. It delves into the dynamics of magnetization, particularly focusing on magnetic moments precession and the corresponding dispersion relationships under two distinct acoustic and optic eigenmodes. Furthermore, it elaborates on a novel hybrid quantum system termed magnon-magnon coupling. The study elucidates the mechanism behind the robust coupling between acoustic and optic magnon modes. Finally, we briefly discuss the current challenges and future research directions in this field.

Strong magnon-magnon coupling in hexagonal magnetic elements

We achieve strong magnon-magnon coupling experimentally between edge and center modes in patterned hexagonal CoFeB films. The coupling strength is adjustable via the external magnetic field’s direction and the nanomagnet’s aspect ratio. Micromagnetic simulation indicates that the stable existence of the center mode determines the occurrence of coupling, which correlates with the direction of the edge demagnetization field. This work offers a novel perspective on the study of magnon-magnon coupling in a single material, which benefits magnon-based quantum information technology.

Ultrastrong magnon-magnon coupling and chiral spin-texture control in a dipolar 3D multilayered artificial spin-vortex ice

Strongly-interacting nanomagnetic arrays are ideal systems for exploring reconfigurable magnonics. They provide huge microstate spaces and integrated solutions for storage and neuromorphic computing alongside GHz functionality. These systems may be broadly assessed by their range of reliably accessible states and the strength of magnon coupling phenomena and nonlinearities. Increasingly, nanomagnetic systems are expanding into three-dimensional architectures. This has enhanced the range of available magnetic microstates and functional behaviours, but engineering control over 3D states and dynamics remains challenging. Here, we introduce a 3D magnonic metamaterial composed from multilayered artificial spin ice nanoarrays. Comprising two magnetic layers separated by a non-magnetic spacer, each nanoisland may assume four macrospin or vortex states per magnetic layer. This creates a system with a rich 16N microstate space and intense static and dynamic dipolar magnetic coupling. The system exhibits a broad range of emergent phenomena driven by the strong inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling with normalised coupling rates of Δfν=0.57\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{\\Delta f}{\ u }=0.57$$\\end{document}, GHz mode shifts in zero applied field and chirality-control of magnetic vortex microstates with corresponding magnonic spectra.

Ultrastrong to nearly deep-strong magnon-magnon coupling with a high degree of freedom in synthetic antiferromagnets

Ultrastrong and deep-strong coupling are two coupling regimes rich in intriguing physical phenomena. Recently, hybrid magnonic systems have emerged as promising candidates for exploring these regimes, owing to their unique advantages in quantum engineering. However, because of the relatively weak coupling between magnons and other quasiparticles, ultrastrong coupling is predominantly realized at cryogenic temperatures, while deep-strong coupling remains to be explored. In our work, we achieve both theoretical and experimental realization of room-temperature ultrastrong magnon-magnon coupling in synthetic antiferromagnets with intrinsic asymmetry of magnetic anisotropy. Unlike most ultrastrong coupling systems, where the counter-rotating coupling strength g2 is strictly equal to the co-rotating coupling strength g1, our systems allow for highly tunable g1 and g2. This high degree of freedom also enables the realization of normalized g1 or g2 larger than 0.5. Particularly, our experimental findings reveal that the maximum observed g1 is nearly identical to the bare frequency, with g1/ω0 = 0.963, indicating a close realization of deep-strong coupling within our hybrid magnonic systems. Our results highlight synthetic antiferromagnets as platforms for exploring unconventional ultrastrong and even deep-strong coupling regimes, facilitating the further exploration of quantum phenomena.

Ultrastrong magnon-magnon coupling in synthetic antiferromagnets induced by interlayer Dzyaloshinskii-Moriya interaction

Ultrastrong magnon-magnon coupling in synthetic antiferromagnets induced by interlayer Dzyaloshinskii-Moriya interaction

Tunable strong magnon-magnon coupling in two-dimensional array of diamond shaped ferromagnetic nanodots

Hybrid magnonics involving coupling between magnons and different quantum particles have been extensively studied during past few years for varied interests including quantum electrodynamics. In such systems, magnons in magnetic materials with high spin density are utilized where the ‘coupling strength’ is collectively enhanced by the square root of the number of spins to overcome the weaker coupling between individual spins and the microwave field. However, achievement of strong magnon-magnon coupling in a confined nanomagnets would be essential for on-chip integration of such hybrid systems. Here, through intensive study of interaction between different magnon modes in a Ni80Fe20 (Py) nanodot array, we demonstrate that the intermodal coupling can approach the strong coupling regime with coupling strength up to 0.82 GHz and cooperativity of 2.51. Micromagnetic Simulations reveal that anticrossing occurs due to change in exchange configuration (symmetry breaking). The coupling strength could be continuously tuned by varying the bias field (H ext) strength and orientation (ϕ), opening routes for external control over hybrid magnonic systems. These findings could greatly enrich the rapidly evolving field of quantum magnonics.

Magnon-magnon coupling mediated by topological edge states

The topology of the photonic bath shows excellent potential to engineer the intriguing interaction properties between light and matter. Here, we study the dielectric resonator array with a zigzag geometry, an analogy of the Su-Schrieffer-Heeger model equipped with peculiar freedom to manipulate the nearest-neighbor coupling strength by the internal interaction. A staggered coupling strength of s-type pillar modes is experimentally achieved via the photonic spin-orbit coupling by employing the zigzag dielectric resonator chain. As a result, we observe that the robust edge states of the zigzag chains manifest themselves with linear polarization for an even number of dielectric resonators but elliptical polarization for an odd number. In addition, by coupling magnons to the topological waveguide, we observe resonant magnon–magnon–edge-state coupling, whose coupling strength is topologically protected. More broadly, our work shows that topological waveguide-QED systems may provide the potential for synthesis and study of many-body states with attractive long-range interaction. Published by the American Physical Society 2024

Control of magnon-magnon coupling in Ni80Fe20 nanocross arrays through system dimensions

Hybrid magnonics, founded on the coherent interplay between magnons and various quasiparticles, provides avenues for quantum transduction and the seamless transmission of coherent information. Magnon-magnon coupling, which exhibits remarkable coupling strength advantages over light-matter interactions, has emerged as a promising field. This research investigates magnon-magnon coupling in Ni80Fe20 nanocross arrays, with a focus on controlling the anticrossing phenomenon. Through a methodical adjustment of the nanocross arm length, it becomes possible to fine-tune the strength of coupling. The significance of the observed effect becomes evident when examining the power and phase profiles of distinct spin-wave (SW) modes in close proximity to and at a considerable distance from the anticrossing point. The research contributes to bridging the gap in hybrid quasi-particle interactions and offers insights into magnon-magnon coupling control. The findings open avenues for efficient magnon-based technologies and systems enabling efficient control of SW propagation characteristics and coupling, with implications for efficient quantum information processing architectures.

Magnon-magnon coupling in synthetic ferrimagnets

Magnon-magnon coupling in synthetic ferrimagnets

Hybrid magnonics in hybrid perovskite antiferromagnets

Hybrid magnonic systems are a newcomer for pursuing coherent information processing owing to their rich quantum engineering functionalities. One prototypical example is hybrid magnonics in antiferromagnets with an easy-plane anisotropy that resembles a quantum-mechanically mixed two-level spin system through the coupling of acoustic and optical magnons. Generally, the coupling between these orthogonal modes is forbidden due to their opposite parity. Here we show that the Dzyaloshinskii–Moriya-Interaction (DMI), a chiral antisymmetric interaction that occurs in magnetic systems with low symmetry, can lift this restriction. We report that layered hybrid perovskite antiferromagnets with an interlayer DMI can lead to a strong intrinsic magnon-magnon coupling strength up to 0.24 GHz, which is four times greater than the dissipation rates of the acoustic/optical modes. Our work shows that the DMI in these hybrid antiferromagnets holds promise for leveraging magnon-magnon coupling by harnessing symmetry breaking in a highly tunable, solution-processable layered magnetic platform.

Functionalized High-Speed Magnon Polaritons Resulting from Magnonic Antenna Effect

Magnon polaritons (MPs) refer to a light-magnon coupled state, which have the potential to act as information carriers, possibly enabling charge-free computation. However, light-magnon coupling is inherently weak. To achieve sufficiently strong coupling, a large ferromagnet or coupling with a microwave cavity is necessary. Thus, we theoretically propose a 100 nm YIG/1 \textmu{}m GGG/500 \textmu{}m YIG structure as a fundamental platform for magnonic and magnon-optical information storage devices to address the aforementioned issues. Furthermore, we discuss the transport properties of the MPs. Owing to the waveguide modes formed by the dielectric constant of the structure, the magnons placed in a nanometer-thin layer are strongly coupled with light. In addition, a longitudinal magnon-magnon coupling between thin and thick magnetic layers yields rich functionalities and a large magnon density to the thick-layer MPs due to the ``magnonic antenna effect.'' Hence, a large, direction-switchable magnon current in the thin layer is observed. The proposed structure indicates a longer coherence length and suitable figure of merit for the magnonic antenna effect. Therefore, the findings of this study would enable the integration of ferromagnetic micro- and nanostructures for MP-based information devices without any restrictions due to cavities.

Distant Magnon-Magnon Coupling Mediated by Nonresonant Photon

In this paper, we theoretically and experimentally study the distant magnon-magnon coupling mediated by nonresonant photons. We establish a magnon-photon-magnon coupling model for two CrCl3 crystals spacial separated on a microstrip line. By changing the phase difference of the samples from 0 to π in order to manipulate the distant magnons from coherent coupling to dissipative coupling, our coupling model predicts that the dispersion is tunable from a level repulsion to a level attraction. In addition, we experimentally demonstrate that two spacial separated CrCl3 crystals over a distance of 1.2 cm couple each other indirectly via the microwave photons on the microstrip line. Our works for the distant magnon-magnon coupling mediated by nonresonant photons might provide new sight into long-distant information transmission.

Tunable magnon-magnon coupling mediated by in-plane magnetic anisotropy in synthetic antiferromagnets

The magnon–magnon coupling is the key issue to exchange information in hybrid magnonic systems. We investigate the magnon–magnon coupling in a synthetic antiferromagnet (SAF) system with the presence of an in-plane uniaxial magnetic anisotropy via micromagnetic simulations. The magnon–magnon coupling arises, and its strength is field-direction dependent. The maximum magnon–magnon coupling occurs when the in-plane magnetic field along 45° deviates from the easy axis. The magnon–magnon coupling can be regulated by the in-plane magnetic anisotropy field. The dynamical phase between two magnetic layers is neither 0° nor 180°, which indicates the magnon in a hybrid mode. This study provides a simple method for a tunable magnon–magnon coupling in SAFs to realize a practical hybrid quantum system based on magnonics.

Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode

Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave excitations between two spatially separated magnetic samples. In this paper, we present a scheme to substantially amplify this transfer efficiency through the application of a two-photon parametric drive on the cavity. Further, we enunciate the physical origin of the enhancement. The recurrent multiphoton absorption by the cavity opens up an infinite ladder of accessible energy levels, which can induce higher-order transitions within the magnon Fock space. This is reflected in a heightened spin-current response from one of the magnetic samples when the neighboring sample is coherently pumped. The enhancement induced by the parametric drive can be considerably high within the stable dynamical region. Specifically, near the periphery of the stability boundary, the spin current is amplified by several orders of magnitude. Such striking enhancement factors are attributed to the emergence of parametrically induced strong coherences precipitated by a long-lived mode, which is analogous to a bound state in continuum. While contextualized in magnonics, the generality of the principle would allow applications to energy transfer between systems contained in parametric cavities.

Magnetoelectric Cavity Magnonics in Skyrmion Crystals

We present a theory of magnetoelectric magnon-photon coupling in cavities hosting noncentrosymmetric magnets. Analogously to nonreciprocal phenomena in multiferroics, the magnetoelectric coupling is time-reversal and inversion asymmetric. This asymmetry establishes a means for exceptional tunability of magnon-photon coupling, which can be switched on and off by reversing the magnetization direction. Taking the multiferroic skyrmion-host Cu$_2$OSeO$_3$ with ultralow magnetic damping as an example, we reveal the electrical activity of skyrmion eigenmodes and propose it for magnon-photon splitting of ``magnetically dark'' elliptic modes. Furthermore, we predict a cavity-induced magnon-magnon coupling between magnetoelectrically active skyrmion excitations. We discuss applications in quantum information processing by proposing protocols for all-electrical magnon-mediated photon quantum gates, and a photon-mediated SPLIT operation of magnons. Our study highlights magnetoelectric cavity magnonics as a novel platform for realizing quantum-hybrid systems and the coherent transduction between photons and magnons in topological magnetic textures.

Magic-angle magnonic nanocavity in a magnetic moiré superlattice

Moir\'e superlattices have recently been extensively studied in both electronic and photonic systems, e.g., magic-angle bilayer graphene showing superconductivity and twisted bilayer photonic crystals leading to magic-angle lasers. However, the moir\'e physics is barely studied in the field of magnonics, i.e., in using spin waves for information processing. In this work, we report magnon flat-band formation in twisted bilayer magnonic crystals at the optimal ``magic angle'' and interlayer exchange coupling combination using micromagnetic simulations. At the flat-band frequency, magnons undergo a strong two-dimensional confinement with a lateral scale of about 185 nm. The magic-angle magnonic nanocavity occurs at the $AB$ stacking region of a moir\'e unit cell, unlike its photonic counterpart which is at the $AA$ region, due to the exchange-induced magnon spin torque. The magnon flat band originates from band structure reformation induced by interlayer magnon-magnon coupling. Our results enable efficient accumulation of magnon intensity in a confined region that is key for potential applications such as magnon Bose-Einstein condensation and even magnon lasing.

Coherent Coupling of Two Remote Magnonic Resonators Mediated by Superconducting Circuits.

We demonstrate microwave-mediated distant magnon-magnon coupling on a superconducting circuit platform, incorporating chip-mounted single-crystal Y_{3}Fe_{5}O_{12} (YIG) spheres. Coherent level repulsion and dissipative level attraction between the magnon modes of the two YIG spheres are demonstrated. The former is mediated by cavity photons of a superconducting resonator, and the latter is mediated by propagating photons of a coplanar waveguide. Our results open new avenues toward exploring integrated hybrid magnonic networks for coherent information processing on a quantum-compatible superconducting platform.

Manipulation of Time- and Frequency-Domain Dynamics by Magnon-Magnon Coupling in Synthetic Antiferromagnets

Magnons (the quanta of spin waves) could be used to encode information in beyond Moore computing applications. In this study, the magnon coupling between acoustic mode and optic mode in synthetic antiferromagnets (SAFs) is investigated by micromagnetic simulations. For a symmetrical SAF system, the time-evolution magnetizations of the two ferromagnetic layers oscillate in-phase at the acoustic mode and out-of-phase at the optic mode, showing an obvious crossing point in their antiferromagnetic resonance spectra. However, the symmetry breaking in an asymmetrical SAF system by the thickness difference, can induce an anti-crossing gap between the two frequency branches of resonance modes and thereby a strong magnon-magnon coupling appears between the resonance modes. The magnon coupling induced a hybridized resonance mode and its phase difference varies with the coupling strength. The maximum coupling occurs at the bias magnetic field at which the two ferromagnetic layers oscillate with a 90° phase difference. Besides, we show how the resonance modes in SAFs change from the in-phase state to the out-of-phase state by slightly tuning the magnon-magnon coupling strength. Our work provides a clear physical picture for the understanding of magnon-magnon coupling in a SAF system and may provide an opportunity to handle the magnon interaction in synthetic antiferromagnetic spintronics.

Strong coupling of quantized spin waves in ferromagnetic bilayers

We formulate a strong-coupling theory for perpendicular standing spin waves (PSSWs) in ferromagnetic bilayers with the interlayer exchange coupling (IEC). Employing the Hoffmann boundary condition and the energy-flow continuity across the interface, we show that the PSSWs are still quantized but with non-integral quantum numbers, in sharp contrast to that of a single layer. The magnon-magnon coupling is characterized by the spectrum splitting which is linear with the IEC in the weak-coupling region, but getting saturated in the strong-coupling limit. Analytical predictions are verified by full micromagnetic simulations with good agreement.