Perspective: Magnon-magnon coupling in hybrid magnonics

TL;DR

This Perspective surveys magnon–magnon coupling as a versatile route to tailor magnon spectra across metal–insulator bilayers, all-insulator heterostructures, 2D AFMs, bulk AFMs, and synthetic ferri-/ferromagnets. It details coupling mechanisms—interfacial exchange, RKKY, DMI, and dipolar interactions—and relates them to device geometries (bilayers, syn-AFMs, nanostructure arrays) and measurable phenomena such as anticrossings, cooperativity, and nonlinear magnon dynamics. The review highlights experimental demonstrations across YIG-based systems, 2D van der Waals magnets CrCl$_3$/CrSBr and CrPS$_4$, bulk oxides like YFeO$_3$, and synthetic multilayer magnets, emphasizing how symmetry breaking, temperature, layer number, and nanostructuring control coupling strength and dispersion. It also discusses integration with magnon–X transduction, Floquet engineering, and on-chip architectures, outlining a vision for programmable, low-damping, multilevel magnonic platforms for coherent information processing and quantum-inspired technologies.

Abstract

The internal coupling of magnetic excitations (magnons) with themselves has created a new research sub-field in hybrid magnonics, i.e., magnon-magnon coupling, which focuses on materials discovery and engineering for probing and controlling magnons in a coherent manner. This is enabled by, one, the abundant mechanisms of introducing magnetic interactions, with examples of exchange coupling, dipolar coupling, RKKY coupling, and DMI coupling, and two, the vast knowledge of how to control magnon band structure, including field and wavelength dependences of frequencies, for determining the degeneracy of magnon modes with different symmetries. In particular, we discuss how magnon-magnon coupling is implemented in various materials systems, with examples of magnetic bilayers, synthetic antiferromagnets, nanomagnetic arrays, layered van der Waals magnets, and (DMI SOT materials) in magnetic multilayers. We then introduce new concept of applications for these hybrid magnonic materials systems, with examples of frequency up/down conversion and magnon-exciton coupling, and discuss what properties are desired for achieving those applications.

Figures (9)

• Figure 1: The field of hybrid magnonics has grown and developed into different ramifications, such as magnon-photon, magnon-phonon, and magnon-light coupling systems, with the goal of developing energy and signal transduction functionalities across different physical platforms. The magnon-magnon coupling is presented as a unique and versatile approach towards inducing and tailoring magnon modes with desirable properties for further hybridization in the various hybrid magnonic contexts, i.e. Magnon + $X$. The Bloch sphere representation shows how hybrid magnonics can perform coherent information processing, e.g. Rabi oscillation and Ramsey interference, as analogous to a two-level system zhang2019electronicallyzhuang2024dynamical. The symbols $\hat{m}_+$ and $\hat{m}_-$ represent some generic single magnon modes (states).
• Figure 2: The various key attributes of magnon-magnon coupling in the context of hybrid magnonics.
• Figure 3: (a) Schematic of coupled magnon-magnon dynamics in a YIG/FM bilayer mediated by interfacial exchange coupling, with uniform mode ($k=0$) excited in the FM layer and the perpendicular standing spin wave mode ($k>0$) excited in the YIG layer. (b) $H_r$-$\omega$ dependence for the YIG PSSW mode (red) and the FM uniform mode (blue) that intersect with each other. YIG uniform mode is also shown in red dashed curve. (c-f) Coherent magnon-magnon coupling in (c) YIG/Co klingler2018spin, (d) YIG/Nichen2018strong, (e) YIG/CoFeBqin2018exchange and (f) YIG/NiFeli2020coherent.
• Figure 4: The various geometries of magnon-magnon coupling in bilayer magnetic heterostructures. (a,b,c): uniform, extended bilayer coupling in which the thickness of the film defines the magnonic cavity, for (b) insulator/metal (Figure taken from Ref.xiong2020probing), and (c) all-insulator systems (Figure taken from Ref. liu2024strong). (d,e,f): the device geometry in which an FM stripe couples locally to an extended YIG film. The excited magnons can propagate along the lateral dimension, and be detected via: (e) dc rectifications, e.g., using spin Hall effect of Pt (Figure taken from Ref. sheng2023nonlocal), or (f) with rf inductive antennas and magneto-optical probes (Figure taken from Ref. qin2021nanoscale). (g,h,i): lateral magnonic cavity in which the FM stripes (h) serve as complementary, local antennas (Figure taken from Ref. liu2018long), or (i) only used to define the cavity boundaries while the excitation is globally sourced otherwise (Figure taken from Ref. santos2023magnon).
• Figure 5: Detecting magnon-magnon coupling in 2D AFM systems. (a) Schematic of microwave absorption experiment with 2D material. (b) Right-handed (RH) and left-handed (LH) magnon modes. (c) Optical and acoustic magnon modes. (d) Strong magnon-magnon coupling between RH and LH modes in CrSBr. (e) Strong magnon-magnon coupling between optical and acoustic modes in CrCl$_3$. The coupling is only activated by breaking in-plane rotational symmetry. (f) Magnetic state alters the exciton resonance energy in CrSBr. (g) Bright and dark magnon modes. (h) Magnon dispersion detected with optical reflectivity measurements in CrSBr. (i) Calculated transient exciton resonance energy shift from the optical (red) and acoustic (blue) magnon modes. (j) Coherent magnon hybridization between bright and dark magnon modes detected by time-resolved measurement. (Figures (a-d) taken from Ref. cham2022anisotropic; (e) taken from Ref. macneill2019gigahertz; (f-j) taken from Ref. diederich2023tunable.)