Spin-wave Coupling Research Articles

Spin-wave mode coupling in the presence of the demagnetizing field in cobalt-permalloy magnonic crystals

We present the results of studies on the non-uniform frequency shift of spin wave spectrum in a two-dimensional magnonic crystal of cobalt/permalloy under the influence of external magnetic field changes. We investigate the phenomenon of coupling of modes and, as a consequence, their hybridization. By taking advantage of the fact that compressing the crystal structure along the direction of the external magnetic field leads to an enhancement of the demagnetizing field, we analyse its effect on the frequency shift of individual modes depending on their concentration in Co. We show that the consequence of this enhancement is a shift in the coupling of modes towards higher magnetic fields. This provides a potential opportunity to design which pairs of modes and in what range of fields hybridization will occur.

Magnonic demultiplexer-switch based on the cluster of coupled ferrimagnetic Mach–Zehnder interferometers

Here we study the spin-wave propagation in a system of Mach–Zehnder interferometers (MZI) based on ferrimagnetic yttrium-iron garnet (YIG) thin film. The angular momentum transfer during the excitation of a surface magnetostatic spin wave and the coupling of the spin-waves inside the adjacent arms of MZIs is studied using the micromagnetic modeling method. The local variation of the YIG magnetization inside the arms of MZI manifests itself both in the phase shift of the propagating spin-wave signal and coupling efficiency in the region where the adjacent arms of MZI are placed in the close proximity to each other. The switching/demultiplexing performance which is reflected in the spatial frequency selection of the spin-wave signal upon dynamical local change of the magnetization in each of four arms of the interferometers is demonstrated. The proposed MZI demonstrates the basis for the realization of the set of logical operations and could serve the facility of add and drop frequencies (channels) to and from a magnonic data bus in frequency division multiplexed magnonic networks. The use of laterally coupled interferometers opens new possibilities for the formation of the logical magnon devices tuned by the local variation of magnetization which could be realized with the locally focused laser heating.

Micromachined Tunable Magnetostatic Forward Volume Wave Bandstop Filter

We have successfully designed, fabricated, and characterized a planar monolithic yttrium iron garnet (YIG) Chebyshev bandstop filter on gadolinium gallium garnet (GGG) substrate with tunable frequency, low insertion loss (IL), and high rejection. This filter is created in YIG micromachining technology that allows direct placement of metal transducers on YIG for strong spin-wave coupling. With an out-of-plane 3900-Oe bias field, the bandstop filter exhibits 55-dB maximum stopband rejection at a center frequency of 6 GHz, with 2-dB passband IL and 37.8-dBm passband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ \mathrm{IIP_3} $</tex-math> </inline-formula> . By applying different bias fields, the stopband center frequency is tuned from 4 to 8 GHz while maintaining more than 30-dB rejection. Incorporated with proper design of tunable compact electromagnet, this new filter design can provide attenuation of spurs appearing across the fifth generation (5G) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$</tex-math> </inline-formula> -band spectrum.

Skyrmion based energy-efficient straintronic physical reservoir computing

Physical Reservoir Computing (PRC) is an unconventional computing paradigm that exploits the nonlinear dynamics of reservoir blocks to perform temporal data classification and prediction tasks. Here, we show with simulations that patterned thin films hosting skyrmion can implement energy-efficient straintronic reservoir computing (RC) in the presence of room-temperature thermal perturbation. This RC block is based on strain-induced nonlinear breathing dynamics of skyrmions, which are coupled to each other through dipole and spin-wave interaction. The nonlinear and coupled magnetization dynamics were exploited to perform temporal data classification and prediction. Two performance metrics, namely Short-Term Memory (STM) and Parity Check (PC) capacity are studied and shown to be promising (4.39 and 4.62 respectively), in addition to showing it can classify sine and square waves with 100% accuracy. These demonstrate the potential of such skyrmion based PRC. Furthermore, our study shows that nonlinear magnetization dynamics and interaction through spin-wave and dipole coupling have a strong influence on STM and PC capacity, thus explaining the role of physical interaction in a dynamical system on its ability to perform RC.

Enhanced spin wave coupling between array of spin torque nano oscillators in magnonic crystal cavities

Spin wave coupling between nano contact spin torque nano oscllators in asymmetric and symmetric array of antidot MC cavities to obtain sustained spin wave oscillations using supercell plane wave method and micromagnetics is discussed. The SWs were excited by injecting a spin-polarized current into a single nano contact in a L3 magnonic crystal cavity(MCC) and radiate like an end-fire antenna. The SW oscillations are then coupled into one of the guided modes of a magnonic crystal waveguide (MCW). The MCC acts as a SW resonator and spin-torque injection as gain. Together they achieve sustainable oscillations in a manner analogous to the behavior of a laser cavity. The phase locking of arrays of cavities arranged symmetrically and asymmetrically on both sides of a MCW is also discussed. Spin waves are radiated like a broadside antenna. The PSD of the broadside case is 28 dB lower than that of the end-fire case. The obtained value from the micromagnetic simulation is used to find the corresponding point in the guided mode of MCW, and this occurs nearer to the edge of the Brillouin zone. We also investigated the point in dispersion where the maximum energy is coupled from MCC to MCW. The spectral characteristics of the broadside coupling were correlated with frequency pulling effects in the laser cavity. Asymmetric spin-torque excitations on either sides of the MCW cause odd frequency peaks in the PSD characteristics. This can be mitigated when we use MC cavities placed symmetrically on both sides of the MCW, and excite spin waves in each cavity. However, spin waves excited in an asymmetric array of cavities add in phase, yielding a power enhancement with an increase in the number of cavities. Spin waves excited in a symmetric array of cavities add out of phase and result in spin-wave decoherence with an increase in the number of cavities.

Reconfigurable Spin-Wave Coupler Based on Domain-Wall Channels

In functional magnonic devices, spin-wave couplers serve a key role in controlling the spin-wave transmission across different magnonic units. Here we study a reconfigurable spin-wave coupler based on domain-wall channels. The design relies on the dipolar interaction between spin waves propagating in neighboring domain walls. The dipolar-coupled spin-wave modes and their propagation in domain walls are analyzed using micromagnetic simulations and analytical calculations. The distance between domain walls and thus the spin-wave coupling strength can be tuned dynamically. Such a feature results in a dynamically manipulatable spin-wave coupler that enables full control over the propagation properties of coupled spin waves. The spin-wave coupler based on domain-wall channels can be achieved in a single magnetic film, avoiding complex nanofabrication, and enabling possibilities in reconfigurable magnonic functional devices.

Enhanced Spin Wave Coupling between Array of Spin Torque Nano Oscillators in Magnonic Crystalcavities

Enhanced Spin Wave Coupling between Array of Spin Torque Nano Oscillators in Magnonic Crystalcavities

Control of the direction of propagation of spin waves in an ensemble of laterally and vertically connected ferrite microstrips

The possibility of controlling the direction of propagation of spin waves in an ensemble of laterally and vertically connected microstrips of iron-yttrium garnet (YIG) is shown by numerical modeling. Using the finite element method, the magnitude of the coupling length of spin waves in lateral and vertical geometries was calculated. The numerical value of the spin wave coupling coefficients was found by the finite element method as a result of solving a system of Maxwell equations with a magnetic permeability tensor obtained from the linearization of the Landau-Lifshitz equation. By integrating the equation of coupled waves, the possibility of changing the direction of propagation of the spin-wave signal in the structure under consideration is shown. The signal transmission spectra obtained in micromagnetic modeling indicate a change in the nature of the localization of the spin wave power in the output sections of the microwave with a change in the frequency at the input of the structure. The system of laterally and vertically connected microwave diodes is an element of interconnections for three-dimensional topologies of magnon networks, while demonstrating the functionality of spatial-frequency signal demultiplexing. Keywords: spin waves, magnonics, lateral structures, magnonic crystal, ensembles of related structures. Keywords: spin waves, magnonics, lateral structures, magnonic crystal, ensembles of related structures.

Enhanced Spin Wave Coupling between Array of Spin Torque Nano Oscillators in Magnonic Crystalcavities

Enhanced Spin Wave Coupling between Array of Spin Torque Nano Oscillators in Magnonic Crystalcavities

Computational micromagnetics based on normal modes: Bridging the gap between macrospin and full spatial discretization

The Landau–Lifshitz equation governing magnetization dynamics is written in terms of the amplitudes of normal modes associated with the micromagnetic system’s appropriate ground state. This results in a system of nonlinear ordinary differential equations (ODEs), the right-hand side of which can be expressed as the sum of a linear term and nonlinear terms with increasing order of nonlinearity (quadratic, cubic, etc.). The application of the method to nanostructured magnetic systems demonstrates that the accurate description of magnetization dynamics requires a limited number of normal modes, which results in a considerable improvement in computational speed. The proposed method can be used to obtain a reduced-order dynamical description of magnetic nanostructures which allows to adjust the accuracy between low-dimensional models, such as macrospin, and micromagnetic models with full spatial discretization. This new paradigm for micromagnetic simulations is tested for three problems relevant to the areas of spintronics and magnonics: directional spin–wave coupling in magnonic waveguides, high power ferromagnetic resonance in a magnetic nanodot, and injection-locking in spin-torque nano-oscillators. The case studies considered demonstrate the validity of the proposed approach to systematically obtain an intermediate order dynamical model based on normal modes for the analysis of magnetic nanosystems. The time-consuming calculation of the normal modes has to be done only one time for the system. These modes can be used to optimize and predict the system response for all possible time-varying external excitations (magnetic fields, spin currents). This is of utmost importance for applications where fast and accurate system simulations are required, such as in electronic circuits including magnetic devices.

Multimode unidirectional spin-wave coupling in an array of non-identical magnonic crystals near band gap frequencies

Using Brillouin light spectroscopy and micromagnetic simulation methods, we show how the intermodal coupling between two magnonic crystals (MCs) affects signals spatial selection with frequency separation during spin-wave transport. We have experimentally demonstrated control of the intermodal coupling of spin waves (SWs) propagating in non-identical magnonic-crystal microwaveguides near the band gap frequency. We show that the spin-wave propagation direction within the MCs of different width can be controlled by the lateral coupling between SWs. Our findings provide an alternative method for signal filtering and separation within magnonic networks for the implementation of magnonic demultiplexers, power dividers, couplers and microwave signal processing devices. based on the lateral array of non-identical MCs.

Voltage-controlled spin-wave intermodal coupling in lateral ensembles of magnetic stripes with patterned piezoelectric layer

Here we report about the strain-tuned dipolar spin-wave coupling in the adjacent system of yttrium iron garnet stripes, which were strain-coupled with the patterned piezoelectric layer. Spatially-resolved laser ablation technique was used for structuring the surface of the piezoelectric layer and electrodes on top of it. Using a phenomenological model based on coupled modes equation, we demonstrate a voltage-controlled intermodal coupling in lateral magnonic stripes. The features of the tunable spin-wave coupling by changing the geometric parameters and the type of magnetization is demonstrated.

Spin waves in Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;-CoFeB spin-wave directional coupler

The spin-wave coupling device is used as a connection unit to solve the connection problem between spin-wave devices. However, the current size is too large in comparison with the nano-scale process, which is caused by the low efficiency of the spin wave within it. Therefore, we propose the spin-wave directional coupler based on Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;-CoFeB coupling which can improve the current dilemma to a certain extent. By filling the gap layer of two spin-wave waveguides (Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;) placed in parallel with CoFeB material, it is found that the dispersion relationship of the spin wave changes in the data calculation of the micromagnetic simulation software Mumax&lt;sup&gt;3&lt;/sup&gt;. The existence of CoFeB makes the transmission efficiency of the spin wave between the two waveguides higher than in the case without any filling, the enhancement effect is about 4 times where coupling length is reduced from the original 2000 nm to 500 nm, which is conducive to the miniaturization and integration of the spin-wave directional coupler design. From the perspective of the entire device, further analysis indicates that owing to the high saturation magnetization of CoFeB (approximately 8 times that of Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;), the effective field in the Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;-CoFeB directional coupler is greatly enhanced, which leads the spin wave dispersion curve in the waveguide to change. At the same time, the energy of the entire system also increases several times, which is mainly caused by the increase of dipole energy and exchange energy. Then a greater contribution of dipole energy is obtained by changing the size of the device. After that, we study the relationship between the coupling length and the device size and the external magnetic field, then draw a general rule which can play a role in designing any directional couplers with similar structures. Finally, our view points are given from the different spin wave excitation frequencies, gap layer filling materials, internal roughness of the directional coupler, and spin wave lifetime by considering the problems that may occur in practical applications with the Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;-CoFeB directional coupler. In conclusion, our proposed Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;-CoFeB directional coupler structure can effectively enhance the coupling efficiency, and it can also provide a new idea for the application of the interaction between composite materials.

Управляемая электрическим полем спин-волновая связь в латеральных ансамблях магнитных микроструктур

In this work, using numerical and experimental studies, we have demonstrated the possibility of controlling the dipole spin-wave coupling in a lateral array of ferromagnetic stripes using local deformations. As an experimental demonstration of the investigated physical processes, a configuration of a magnonic structure with a piezoelectric layer and structured electrodes on its surface is proposed, and the technique of laser ablation with spatial resolution is used to structure the piezoelectric layer. The mechanisms for controlling the dipole coupling of spin waves by creating elastic deformations localized in the region of the maximums of the electric field are revealed. From an applied point of view, the results obtained can be used to create a class of information processing devices, such as demultiplexing systems with frequency-space selectivity, controlled simultaneously by an electric and magnetic field.

Strain reconfigurable spin-wave transport in the lateral system of magnonic stripes

We demonstrate the possibility of controlling dipole spin-wave coupling in the lateral array of ferromagnetic stripes using local strains. Lateral system of magnonic stripes with a piezoelectric layer is fabricated and tested with microwave and Brillouin light scattering spectroscopy. The mechanisms of controlling the dipole coupling of spin waves by elastic strains localized in the region of maximums of the electric field strength are revealed. It is shown that when the absolute value and sign of the electric field are changed, it is possible to effectively control the properties of the propagating spin waves and the spatial distribution of the intensity of the dynamic magnetization in the lateral structure. We emphasize that the spin-wave intermodal coupling can be tuned with the external electric field in the adjacent magnonic stripes. Formation of channel for spin-wave edge mode propagation is observed experimentally in the vicinity of the gap between adjacent stripes. Effective control of the spin-wave coupling by changing the gap is demonstrated. From an applied point of view, the results can be used in information processing devices with electric and magnetic field tunability.

Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite

Coupling of spin-waves with electromagnetic cavity field is demonstrated in an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at 0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures were found at crossings of spin-wave resonances with Fabry-Perot cavity modes formed in samples. The obtained spectra are explained in terms of classical electrodynamics and a microscopic model.

Intensity and magnetization angle reconfigurable lateral spin-wave coupling and transport

Magnonic directional coupler is important unit of the integrated functional magnonic networks. Here we report on the mechanism of the variation of the spin-wave coupling length which is equal to the longitudinal spatial scale of wave intensity modulation along the magnonic stripes placed in the proximity. The array of yttrium-iron garnet films was proposed to be the main unit of the magnonic directional coupler system. The simultaneous variation of the magnetization orientation and spin-wave intensity leads to the variation of spin-wave coupling length. Using the finite element numerical simulation and numerical integration of the phenomenological equations similar to the nonlinear Ginzburg-Landau equations the dispersion and frequency dependences of the spin wave coupling length were obtained. We also demonstate experimentally the simultaneous control of spin-wave transport by the variation of the signal intensity and magnetization angle. It was shown that the proposed dual-mode control can enhance the functionality of directional coupler, power splitter and multiplexer based on coupled stripes in planar magnonic networks.

Spin-wave confinement and coupling in organic-based magnetic nanostructures

Vanadium tetracyanoethylene (V[TCNE]x) is an organic-based ferrimagnet that exhibits robust magnetic ordering (TC of over 600 K), high quality-factor (high-Q) microwave resonance (Q up to 3500), and compatibility with a wide variety of substrates and encapsulation technologies. Here, we substantially expand the potential scope and impact of this emerging material by demonstrating the ability to produce engineered nanostructures with tailored magnetic anisotropy that serve as a platform for the exploration of cavity magnonics, revealing strongly coupled quantum confined standing wave modes that can be tuned into and out of resonance with an applied magnetic field. Specifically, time-domain micromagnetic simulations of these nanostructures faithfully reproduce the experimentally measured spectra, including the quasiuniform mode and higher-order spin-wave (magnon) modes. Finally, when the two dominant magnon modes present in the spectra are brought into resonance by varying the orientation of the in-plane magnetic field, we observe anticrossing behavior, indicating strong coherent coupling between these two magnon modes at room temperature. These results position V[TCNE]x as a leading candidate for the development of coherent magnonics, with potential applications ranging from microwave electronics to quantum information.

Magnon Straintronics to Control Spin-Wave Computation: Strain Reconfigurable Magnonic-Crystal Directional Coupler

The effect of electrical field control of the spin-wave spectrum in adjacent magnonic crystals stripes was investigated by micromagnetic simulation, microwave spectroscopy, and Brillouin light scattering (BLS). The electric-field-induced dipolar coupling between magnetic stripes leads to the formation of symmetric and antisymmetric collective modes in the spectra of propagating spin waves. In particular, the strain-induced variation of the spin-wave coupling length in the stripe, predicted by micromagnetic simulation and measured by BLS, show the possibility of application of a lateral array of magnonic crystals as tunable microwave directional couplers, power dividers, and spin-wave demultiplexers, which can be used simultaneously as an interconnection unit in reconfigurable magnonic networks.

Tailoring coupling between light and spin waves with dual photonic–magnonic resonant layered structures

We report on judiciously designed stratified periodic structures of magnetic dielectric materials with a localized defect layer, which are able to concurrently confine light and spin waves in the same ultra-small defect region for a long time period, thus resulting in enhanced photon–magnon interaction and large dynamic optical frequency shift. Our results for a specific realization of such a one-dimensional, so-called photomagnonic, crystal magnetized at saturation perpendicular to the interfaces, obtained by means of rigorous calculations using scattering-matrix techniques, show that the inherently weak coupling between visible/near-infrared light and GHz-frequency spin waves can be greatly increased leading to strong modulation of the optical field through multi-magnon exchange mechanisms. Such novel multifunctional composite materials offer a promising platform for tailoring light–spin-wave coupling in view of fast and energy-efficient spin-optical information processing applications.