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1. Spin excitations and dynamics in 2D magnets: An overview of magnons and magnetic skyrmions

   https://doi.org/10.1016/j.pquantelec.2025.100564  

   Wu, Yingying; Balicas, Luis; Cheng, Ran; Zhang, Xiao-Xiao (April 2025, Progress in Quantum Electronics)

   van der Waals magnetic materials open up exciting possibilities to investigate fundamental spin properties in low-dimensional systems and to build compact functional spintronic structures. This review focuses on the recent progress in two-dimensional(2D) magnets that explore beyond the homogenous magnetically-ordered state, including magnons (spin waves), magnetic skyrmions, and complex magnetic domains. Properties of these spin and topology excitations in 2D magnets provide insights into spin-orbit interactions and other forms of coupling between electrons, phonons, and spin-dependent excitations. Such spin-based quasiparticles can also serve as information carriers for next-generation high-speed computing elements. We will first lay out the general theoretical basis of dynamical responses in magnetic systems, followed by detailed descriptions of experimental progress in magnons and spin textures (including magnetic domains and skyrmions). Discussion on the experimental techniques and future perspectives are also included. 

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2. Magnetoelastic coupling driven magnon gap in a honeycomb antiferromagnet

   https://doi.org/10.1103/PhysRevB.110.104419  

   Choe, Jeongheon; Baydin, Andrey; Ye, Gaihua; Ma, Bowen; Nnokwe, Cynthia; Rodriguez-Vega, Martin; Lujan, David; Chaudhary, Swati; Tay, Fuyang; He, Jiaming; et al (September 2024, Physical Review B)

   Cobalt titanate, CoTiO3, is a honeycomb antiferromagnet recently confirmed experimentally to host Dirac magnons, topological spin-orbit excitons, and chiral phonons. Here, we investigate a magnon gap at the zone center which calls for a refined spin Hamiltonian. We propose a microscopic model for the magnon gap and attribute it to a lattice-distortion (phonon)-induced higher-order spin interaction. Strong magnetoelastic coupling in CoTiO3 is also evident in Raman spectra, in which the magnetic order exerts a stronger influence on phonons corresponding to in-plane ionic motions than those with out-of-plane motions. We further examine the evolution of the zone-center magnons in a high magnetic field up to 18.5 T via THz absorption spectroscopy measurements. Based on this field dependence, we propose a spin Hamiltonian that not only agrees with magnon dispersion measured by inelastic neutron scattering but also includes fewer exchange constants and a realistic anisotropy term. Our work highlights the broad implications of magnetoelastic coupling in the study of topologically protected bosonic excitations. 

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3. Gapless Dirac magnons in CrCl3

   https://doi.org/10.1038/s41535-022-00473-3  

   Schneeloch, John A.; Tao, Yu; Cheng, Yongqiang; Daemen, Luke; Xu, Guangyong; Zhang, Qiang; Louca, Despina (December 2022, npj Quantum Materials)

   Abstract Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX 3 (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr 3 and CrI 3 , gapless Dirac magnons are present in bulk CrCl 3 , with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above T N . Moreover, on cooling below ~50 K, an anomalous increase in the a -axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above T N . 

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4. Lattice-induced spin dynamics in Dirac magnet CoTiO3

   https://doi.org/10.1063/5.0282888  

   Baydin, A; Luo, J; He, Z; Doumani, J; Lin, T; Tay, F; He, J; Zhou, J; Khalsa, G; Kono, J; et al (October 2025, Journal of Applied Physics)

   Spin–lattice coupling is crucial for understanding the spin transport and dynamics for spintronics and magnonics applications. Recently, cobalt titanate (CoTiO3), an easy-plane antiferromagnet, has been found to host axial phonons with a large magnetic moment, which may originate from spin–lattice coupling. Here, we investigate the effect of light-driven lattice dynamics on the magnetic properties of CoTiO3 using time-resolved spectroscopy with a terahertz pump and a magneto-optic probe. We found resonantly driven Raman-active phonons, phonon–polariton-induced excitation of the antiferromagnetic magnons, and a slow increase in the polarization rotation of the probe, all indicating symmetry breaking that is not intrinsic to the magnetic space group. The temperature dependence confirmed that the observed spin dynamics is related to the magnetic order, and we suggest surface effects as a possible mechanism. Our results of THz-induced spin–lattice dynamics signify that extrinsic symmetry breaking may contribute strongly and unexpectedly to light-driven phenomena in bulk complex oxides. 

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5. Tunable magnons of an antiferromagnetic Mott insulator via interfacial metal-insulator transitions

   https://doi.org/10.1038/s41467-025-58922-z  

   Shrestha, Sujan; Souri, Maryam; Dietl, Christopher J; Pärschke, Ekaterina M; Krautloher, Maximilian; Calderon_Ortiz, Gabriel A; Minola, Matteo; Shi, Xiatong; Boris, Alexander V; Hwang, Jinwoo; et al (April 2025, Nature Communications)

   Antiferromagnetic insulators present a promising alternative to ferromagnets due to their ultrafast spin dynamics essential for low-energy terahertz spintronic device applications. Magnons, i.e., quantized spin waves capable of transmitting information through excitations, serve as a key functional element in this paradigm. However, identifying external mechanisms to effectively tune magnon properties has remained a major challenge. Here we demonstrate that interfacial metal-insulator transitions offer an effective method for controlling the magnons of Sr2IrO4, a strongly spin-orbit coupled antiferromagnetic Mott insulator. Resonant inelastic x-ray scattering experiments reveal a significant softening of zone-boundary magnon energies in Sr2IrO4 films epitaxially interfaced with metallic 4d transition-metal oxides. Therefore, the magnon dispersion of Sr2IrO4 can be tuned by metal-insulator transitions of the 4d transition-metal oxides. We tentatively attribute this non-trivial behavior to a long-range phenomenon mediated by magnon-acoustic phonon interactions. Our experimental findings introduce a strategy for controlling magnons and underscore the need for further theoretical studies to better understand the underlying microscopic interactions between magnons and phonons. 

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