Properties Of Magnons Research Articles

Studying magnon band topology through low-energy magnon excitations: role of anisotropic Dzyaloshinskii-Moriya interaction.

In this work, we study topological properties of magnons via creating spin excitations in both ferromagnets and antiferromagnets in presence of an external magnetic field on a two-dimensional square lattice. It is known that Dzyaloshinskii-Moriya interaction (DMI) plays an important role in coupling between different particle (spin excitation) sectors, here we consider an anisotropic DMI and ascertain the role of the anisotropy parameter in inducing topological phase transitions. While the scenario, for dealing with ferromagnets, albeit with isotropic DMI is established in literature, we have developed the formalism for studying magnon band topology for the antiferromagnetic case. The calculations for the ferromagnetic case are included to facilitate a comparison between the two magnetically ordered systems. Owing to the presence of a two-sublattice structure of an antiferromagnet, a larger number of magnon bands participate in deciding upon the topological properties. However, in both the cases, an extended trivial region is observed even with the DMI to be non-zero, which is surprising since the DMI is the origin of the finite Berry curvature in presence of external magnetic field. The nature of the phases in both the cases and the phase transitions therein are characterized via computing the band structure, ascertaining the presence (or absence) of the chiral edge modes observed in a semi-infinite nano-ribbon geometry, and investigation of the thermal Hall effect. Moreover, the strength of the magnetic field is found to play a decisive role in controlling the critical point that demarcates various topological phases.

Handedness manipulation of propagating antiferromagnetic magnons

Antiferromagnetic magnons possess a distinctive feature absent in their ferromagnetic counterparts: the presence of two distinct handedness modes, the right-handed (RH) and left-handed (LH) precession modes. The magnon handedness determines the sign of spin polarization carried by the propagating magnon, which is indispensable for harnessing the diverse functionalities in magnonic devices, such as data encoding, magnon polarization-based logic systems, and quantum applications involving magnons. However, the control of coherently propagating magnon handedness in antiferromagnets has remained elusive. Here we demonstrate the manipulation and electrical readout of propagating magnon handedness in perpendicularly magnetized synthetic antiferromagnets (SAF). We find that the antiferromagnetic magnon handedness can be directly identified by measuring the inverse spin Hall effect (ISHE) voltage, which arises from the spin pumping effect caused by the propagating antiferromagnetic magnons in the SAF structure. The RH and LH modes of the magnon can be distinguishable when the SAF structure is sandwiched by heavy metals with the same sign of spin Hall angle. This work unveils promising avenues for harnessing the unique properties of antiferromagnetic magnons.

Magnon-mediated optical frequency comb in a cavity optomagnonical system

Generally, optical frequency combs (OFC) are generated through nonlinear effects in optical pumping, such as Kerr nonlinearity, the electro-optic effect, and second-order nonlinearity. Here, we propose an effective mechanism for generating OFC in a cavity optomagnonical system via the nonlinearity of magnon-photon coupling. Our results demonstrate that robust OFC can be achieved in this system when driven by effective nanosecond pulses in the non-perturbation regime. Notably, the addition of an extra microwave pump field can enhance magnon-photon coupling and reduce the system’s reliance on the optical pump field. Furthermore, the number and spacing of the OFC teeth can be adjusted by selecting appropriate experimental parameters. These findings contribute to a deeper understanding of the quantum and nonlinear properties of magnons and pave the way for the development of OFC devices in integrated optics and photonics.

Unconventional magnon blockade in a dissipative photon–magnon coupling system

We investigate unconventional magnon blockade (UMB) in a dissipative photon–magnon coupling cavity, where the coherent and dissipative coupling between photon and magnon can be adjusted by the position of the yttrium iron garnet sphere in the cavity. An approximate analytical solution for the statistical property of magnon is provided, which is in good agreement with the results obtained by numerically solving the Lindblad master equation. Our results indicate that UMB can be achieved in the case of dissipative photon–magnon coupling, but not in the case of coherent photon–magnon coupling. Secondly, by adjusting the amplitude of the external laser field, dynamic control of UMB can be achieved. Finally, by solving the Lindblad master equation containing the occupation number of thermal magnon and photon, the statistical properties of magnons will transition from nonclassical to classical. It is shown that the above phenomena originate from the interference between different quantum paths. Our research may provide theoretical possibilities for quantum manipulation schemes at the single-magnon level and open up a new avenue for designing single-magnon sources in a dissipative photon–magnon coupling system.

Generating grating in cavity magnomechanics

Abstract We investigate the phenomenon of magnomechanically induced grating (MMIG) within a cavity magnomechanical system, comprising magnons (spins in a ferromagnet, such as yttrium iron garnet), cavity microwave photons, and phonons (Li et al 2018 Phys. Rev. Lett. 121 203601). By applying an external standing wave control, we observe modifications in the transmission profile of a probe light beam, signifying the presence of MMIG. Through numerical analysis, we explore the diffraction intensities of the probe field, examining the impact of interactions between cavity magnons, magnon-phonon interactions, standing wave field strength, and interaction length. MMIG systems leverage the unique properties of magnons, and collective spin excitations with attributes like long coherence times and spin-wave propagation. These distinctive features can be harnessed in MMIG systems for innovative applications in information storage, retrieval, and quantum memories, offering various orders of diffraction grating.

The importance of long range Fe–Fe interactions in magnetically ordered 2D Fe0.2Ni0.8/Ni(001) and Fe0.3Ni0.7/Ni(001) alloy systems

We develop a theoretical approach to study the magnonic properties of the 2D ordered surface Fe–Ni alloys with 20% and 30% Fe on a face-centered cubic Ni(001) surface substrate. The surface alloy nanostructures in stable equilibrium are determined by computing the lowest energy configurations of constitutive supercells of the ordered alloys. The magnetic exchange constants of the ground state of the stable systems are calculated to define their Heisenberg Hamiltonians using the DFT Spin-Polarized Relativistic Korringa–Kohn–Rostoker (SPRKKR) method and considering Fe–Fe interactions up to third nearest neighbors. To determine the propagating exchange spin-wave modes, evanescent modes, and the consequent magnonic properties, the spin dynamics of the magnetic surface alloy nanostructures are solved using the phase field matching theory (PFMT). Our results indicate that the Fe–Fe exchange interactions up to third nearest neighbors are vital for accurately describing their magnonics. In particular, the exchange interactions influence the form of dispersion branches for the high-energy spin-wave modes of the Fe–Ni surface alloys considered. Appropriate Green’s functions are also derived from the PFMT method to compute the local densities of states (LDOS) for the atomic sites at the surface boundary. For the case of 20% Fe surface alloy, the Fe–Fe exchange interactions shift the Fe LDOS peaks to lower frequency intervals. We also distinguish the emergence of remarkable LDOS peaks for the he case of the 30% Fe surface alloy at specific Ni sites. These peaks change positions under second and third nearest neighbor Fe–Fe interactions, heralding new accessible spin-wave channels. Our results contribute to establishing a systematic understanding of the magnonics of the magnetic surface alloys of transition metal (TM) materials. This new knowledge will enable the study of the quantum transport of spin waves at interfacial alloy nanojunctions composed of such materials. The present DFT-PFMT theoretical approach is general and can be applied to other surface TM alloy magnetic nanostructures.

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 μm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

NiO thin films fabricated using spray-pyrolysis technique: structural and optical characterization and ultrafast charge dynamics studies

Nickel (II) oxide, NiO, is a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displays antiferromagnetic order at room temperature. NiO has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the fabrication of polycrystalline NiO using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. The composition and structure of the NiO thin films were then studied using x-ray diffraction, and atomic force and scanning electron microscopies (SEM). The phononic and magnonic properties of the NiO thin films were also studied via Raman spectroscopy, and the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that the NiO samples display the same phonon and magnon excitations expected for single crystal NiO at room temperature, and that electron dynamics in our system is like those of previously reported NiO mono- and polycrystalline systems synthesized using different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthesize strongly correlated materials for a large set of applications.

Magnon bands and transverse transport in a proposed two-dimensional [formula omitted] ferrimagnet

The copper fluoride Cu2F5 is a proposed stable compound that can be seen as a layered lattice of S=1 and S=1/2 sites, corresponding to copper ions. Intending to cast light on the transport properties of ferrimagnetic magnons, we use the linear spin wave approach to study the magnon band structure of the 2D lattice in a ferrimagnetic off-plane order, as well as the transverse transport of magnons in the crystal bulk. A magnetic field or temperature gradient can induce transverse (Hall-like) transport within the linear response theory generated by the Berry curvature of the eigenstates. As in most cases involving magnons, the Berry curvature is related to Dzyaloshinskii–Moriya interactions between next-near-neighbors The band structure of the system is non-degenerate and the transport coefficients are non-null. The novel and interesting feature of the system is that, within certain conditions, the transport coefficients versus temperature curves are non-monotonic and present a sign change, opening the exciting possibility of controlling the transverse magnon flow direction and magnitude with the temperature change.

Dynamic and magnetic properties of excited magnons in tetragonal fcc [formula omitted]/SiO multilayer alloys

In this paper, we investigate by numerical lattice simulations the magnetic and dynamic properties of excited magnons in d transition metal alloys FexPt1−x/SiO using Green functions and second quantification techniques. The sandwich structure consists of magnetic (FePt) and non-magnetic (SiO) layers. The corresponding quantum Heisenberg Hamiltonian includes exchange interactions, magnetocrystalline anisotropy, surface anisotropy and magnetic field. The existence of the surface magnons is demonstrated by the surface creation factor η, which is in good agreement with the measured lifetime data. Surface magnons are characterized by their excitation spectrum, susceptibility of creation, creation gap, permitted band for creation, and lifetime, which are different from volume magnons properties. The susceptibility of creation analysis is compatible with experimental values, and the calculated lifetimes are in the order of femtoseconds (fs) reproducing the analytical behavior of the measured values along the lattice symmetry axis. The surface magnons are found to be more confined in time and space than those excited in volume, indicating the presence of short-range spin correlations. Magnetization per spin versus temperature is also calculated for different iron concentrations x and found to be in excellent agreement with the measured values. Also, the response of the system to an external magnetic field is shown for xFe=0.29 with various temperature values, and it agrees well with the experience.

Reciprocity relations in a biologically inspired nanomagnonic system with dipolar coupling

Magnetosome chains in magnetotactic bacteria present ideal nanomagnonic model systems for studying collective resonance modes of dipolar-coupled single domain particles in relation to their spatial arrangement. Using microresonator-based ferromagnetic resonance (FMR) spectroscopy, electron microscopy, and micromagnetic modeling, we here provide insights into the complex magnonic activity within a single magnetosome chain. While the angular dependence of its FMR spectrum is dominated by twofold symmetry features due to the uniaxial anisotropy of linear chain segments, we also observed an unexpected behavior such as interrupted lines and flat bands due to the intricate geometrical details of this particular chain, such as a cross-like structural anomaly where a pair of particles is oriented perpendicular to the main axis of the chain and thus breaks the prevailing axial dipolar coupling symmetry. Such a cross junction formed by four particles exhibits interesting magnonic network properties. Notably, we observe reciprocity in the sense that the spectral response of one particle to an excitation of another one is identical to the response of the latter given an excitation of the former. Furthermore, we have identified that magnonic coupling between A and B can be facilitated via a dark state, as in magnonic stimulated Raman adiabatic passage, and that this dark-state coupling can be made non-reciprocal between A and B by breaking the symmetry of the spatial arrangement of the four particles.

Topological band engineering and tunable thermal Hall effect in trimerized Lieb lattice ferromagnets

We theoretically study the topological properties of magnons and the relevant magnon thermal Hall effect in trimerized Lieb lattice ferromagnets in the presence of next-nearest-neighbor Dzyaloshinskii-Moriya interactions. By calculating the magnon band structures and their Chern numbers with the linear spin-wave theory, we show that the system can undergo a phase transition between a magnonic topological insulator phase and a magnonic trivial insulator phase. The main results are presented in the form of topological phase diagrams, where the Chern numbers or magnon thermal Hall conductivity are shown as a function of the two lattice trimerization parameters. We find a sharp change of the thermal Hall conductivity across the critical point of phase transformations associated with topological nontrivial edge states. The behaviors reflect that the existence of trimerizations breaks the C4 rotational symmetry of the Lieb lattice. Finally, we show that our theoretical predictions could be experimentally realized in high-temperature cuprate superconductors or organic magnetic materials. Published by the American Physical Society 2024

Photoinduced topological phase transitions in Kitaev-Heisenberg honeycomb ferromagnets with the Dzyaloshinskii-Moriya interaction

We theoretically study topological properties of Floquet magnons in a laser-irradiated Kitaev-Heisenberg honeycomb ferromagnet with the Dzyaloshinskii-Moriya interaction by making use of the Floquet-Bloch theory. It is found that the Kitaev-Heisenberg honeycomb ferromagnet can reveal two topological phases with different Chern numbers when it is irradiated by the circular-polarized light. We find that the topological phase of the system can be switched from one topological phase to another one by adjusting the light intensity. The intrinsic Dzyaloshinskii-Moriya interaction plays a crucial role in the emergence of photoinduced topological phase transitions. It is shown that sign reversal of the thermal Hall conductivity is an important indicator on photoinduced topological phase transitions in the Kitaev-Heisenberg honeycomb ferromagnet.

Nonequilibrium steady-state transport properties of magnons in ferromagnetic insulators

Understanding nonequilibrium transport phenomena in bosonic systems is highly challenging. Magnons, as bosons, exhibit different transport behavior from fermionic electron spins. This study focuses on the key factors influencing the nonequilibrium transport of magnons in steady states within magnetic insulators by taking Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> (YIG) for example. By incorporating the Bose-Einstein distribution function with a non-zero chemical potential <inline-formula><tex-math id="M15">\begin{document}$ {\mu }_{m} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M15.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M15.png"/></alternatives></inline-formula> into the Boltzmann transport equation, analytical expressions for transport parameters in power of <inline-formula><tex-math id="M16">\begin{document}$ \alpha $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M16.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M16.png"/></alternatives></inline-formula> (<inline-formula><tex-math id="M17">\begin{document}$ =-{\mu }_{{\mathrm{m}}}/({k}_{{\mathrm{B}}}T) $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M17.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M17.png"/></alternatives></inline-formula>) are obtained under the condition <i>α</i><1. It is the biggest different from previous researches that our theory establishes a nonlinear relationship between the chemical potential and the nonequilibrium particle density <inline-formula><tex-math id="M18">\begin{document}$ \delta {n}_{{\mathrm{m}}}\propto -{\alpha }^{1/2}\propto $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M18.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M18.png"/></alternatives></inline-formula><inline-formula><tex-math id="M18-1">\begin{document}$ -{(-{\mu }_{{\mathrm{m}}})}^{1/2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M18-1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M18-1.png"/></alternatives></inline-formula> for magnons under <i>α</i><inline-formula><tex-math id="Z-20240629142100">\begin{document}$\ll 1 $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_Z-20240629142100.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_Z-20240629142100.png"/></alternatives></inline-formula>. For a large chemical potential, higher-order terms of <i>α</i> must be taken into account. Owing to this nonlinear relationship, the magnon diffusion equation markedly differs from that governing electron spin,which evolves into more complex nonlinear differential equation. We specifically focus on the ferrimagnetic insulator YIG by making a comparison of the spatial distribution of the nonequilibrium magnon density <inline-formula><tex-math id="M19">\begin{document}$ \delta {n}_{m} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M19.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M19.png"/></alternatives></inline-formula> and chemical potential <inline-formula><tex-math id="M20">\begin{document}$ {\mu }_{m} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M20.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M20.png"/></alternatives></inline-formula> between two extreme temperature gradients, namely, <inline-formula><tex-math id="M21">\begin{document}$ \nabla T \sim 1\;{\mathrm{K}}/{\mathrm{m}}{\mathrm{m}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M21.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M21.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M22">\begin{document}$ {10}^{4}\;{\mathrm{K}}/{\mathrm{m}}{\mathrm{m}}, $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M22.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M22.png"/></alternatives></inline-formula> which correspond to <inline-formula><tex-math id="M23">\begin{document}$ {\mu }_{{\mathrm{m}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M23.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M23.png"/></alternatives></inline-formula> values on the order of <inline-formula><tex-math id="M24">\begin{document}$ -0.1\;{\text{μ}}{\mathrm{e}}{\mathrm{V}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M24.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M24.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M25">\begin{document}$ -6.2\;{\mathrm{m}}{\mathrm{e}}{\mathrm{V}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M25.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M25.png"/></alternatives></inline-formula>, respectively, while still satisfying the prerequisite <i>α</i> < 1. Given the known temperature gradient distribution, the nonequilibrium magnon density <inline-formula><tex-math id="M26">\begin{document}$ \delta {n}_{{\mathrm{m}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M26.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20240498_M26.png"/></alternatives></inline-formula> calculated based on our theory is in good agreement with the experimental result. Our theoretical and numerical findings greatly contribute to a profound understanding of the nonequilibrium magnon transport characteristics in magnetic insulators.

Exceptional-point-engineered phonon laser in a cavity magnomechanical system

We propose a scheme to engineer phonon laser in a non-Hermitian cavity magnomechanical (CMM) system with dissipative magnon-photon coupling. The exceptional point (EP) (the analog of the -symmetric regime), emerging in the system and changing the properties of photons, magnons, and phonons, can be observed with a tunable dissipative magnon-photon coupling caused by the cavity Lenz’s law. At the EP, we find that a strong nonlinear relation appears between the mechanical amplification factor and the detuning parameter, which results in a dramatic enhancement of magnetostrictive force and mechanical gain, and leading to the highly efficient phonon laser and the ultralow threshold power. Furthermore, EP induced by dissipative coupling is flexible and tunable compared to the -symmetric regime, and the ultralow threshold power phonon laser is immune to the loss rates of the photon and magnon modes. Our scheme provides a theoretical basis for phonon laser in non-Hermitian systems and presents potential applications ranging from preparing coherent phonon sources to operating on-chip functional acoustic devices.

Influence of nonlocal damping on magnon properties of ferromagnets

Influence of nonlocal damping on magnon properties of ferromagnets

Tuning bulk topological magnon properties with light-induced magnons

Although theoretical modeling and inelastic neutron scattering measurements have indicated the presence of topological magnon bands in multiple quantum magnets, experiments remain unable to detect a signal of the magnon thermal Hall effect in the quantum magnets, which is a consequence of magnons condensation at the bottom of the bands following Bose-Einstein statistics as well as the concentration of Berry curvature at the higher energies. In recent work, Malz et al. [Nat. Commun. 10, 3937 (2019)] have shown that topological magnons in edge states in a finite sample can be amplified using tailored electromagnetic fields. We extend their approach by showing that a uniform electromagnetic field can selectively amplify magnons with finite Berry curvature by breaking the inversion symmetry of a lattice. Using this approach, we demonstrate the generation of bulk topological magnons in a Heisenberg ferromagnet on the breathing kagome lattice and the consequent amplification of the thermal Hall effect.

Magnon dynamics in a skyrmion-textured domain wall of antiferromagnets

We theoretically investigate the interaction between magnons and a Skyrmion-textured domain wall in a two-dimensional antiferromagnet and elucidate the resultant properties of magnon transport. Using supersymmetric quantum mechanics, we solve the scattering problem of magnons on top of the domain wall and obtain the exact solutions of propagating and bound magnon modes. Then, we find their properties of reflection and refraction in the Skyrmion-textured domain wall, where magnons experience an emergent magnetic field due to its non-trivial spin texture-induced effective gauge field. Based on the obtained scattering properties of magnons and the domain wall, we show that the thermal transport decreases as the domain wall's chirality increases. Our results suggest that the thermal transport of an antiferromagnet is tunable by modulating the Skyrmion charge density of the domain wall, which might be useful for realizing electrically tunable spin caloritronic devices.

Evaluation protocol for revealing magnonic contrast in TR-STXM measurements

We present a statistically motivated method to extract magnonic contrast from time-resolved scanning transmission x-ray microscopy (TR-STXM) measurements. TR-STXM is an element-specific method for resolving spin-dynamics in space and time. It offers nanometer spatial resolution and picosecond temporal resolution. The presented method makes it possible to obtain phase and amplitude profiles of spin-waves from STXM measurements. Furthermore, it allows for a rigorous transformation to reciprocal magnon k⃗-space, revealing k⃗-dependent magnon properties such as the magnon dispersion in three dimensions and for all directions of the magnetic anisotropy. We demonstrate our method using X-band ferromagnetic resonance on a micrometer-sized permalloy assembly.

Large Anomalous Frequency Shift in Perpendicular Standing Spin Wave Modes in BiYIG Films Induced by Thin Metallic Overlayers.

Interface-driven effects on magnon dynamics are studied in magnetic insulator-metal bilayers using Brillouin light scattering. It is found that the Damon-Eshbach modes exhibit a significant frequency shift due to interfacial anisotropy generated by thin metallic overlayers. In addition, an unexpectedly large shift in the perpendicular standing spin wave mode frequencies is also observed, which cannot be explained by anisotropy-induced mode stiffening or surface pinning. Rather, it is suggested that additional confinement may result from spin pumping at the insulator-metal interface, which results in a locally overdamped interface region. These results uncover previously unidentified interface-driven changes in magnetization dynamics that may be exploited to locally control and modulate magnonic properties in thin-film heterostructures.