Magnon Frequency Research Articles

Low-lying magnon frequency comb in skyrmion crystals

Low-lying magnon frequency comb in skyrmion crystals

Anisotropic magnon frequency comb based on antiferromagnetic bimerons

The interaction between propagating magnons and topological spin textures is attracting a lot of recent attention from the magnonic community. It has been shown that the three-wave mixing between magnons and breathing skyrmion can induce the magnon frequency comb (MFC) with equidistant coherent peaks. However, a magnetic bimeron is a nontrivial spin texture and is regarded as the counterpart of the skyrmion in easy-plane magnets with Dzyaloshinskii–Moriya interaction, which allows anisotropic magnon propagations. This raises the question of whether the nonlinear interaction between magnons and bimerons can generate an MFC. If so, how does the direction of magnon propagation affect the characteristics of the MFC? In this Letter, we demonstrate that the three-wave mixing between propagating magnons and locally breathing bimerons can induce a terahertz MFC in easy-plane antiferromagnets. Micromagnetic simulations reveal that the three-wave coupling strength weakly depends on the driving frequency, but it strongly relies on the propagation direction of incident magnons. Our findings uncover the anisotropic nature of MFC in bimeron structures, which may have potential applications for ultrafast magnonic devices with spectroscopy, metrology, and sensing functionalities.

Two-dimensional coherent spectrum of high-spin models via a quantum computing approach

We present and benchmark a quantum computing approach to calculate the two-dimensional coherent spectrum (2DCS) of high-spin models. Our approach is based on simulating their real-time dynamics in the presence of several magnetic field pulses, which are spaced in time. We utilize the adaptive variational quantum dynamics simulation algorithm for the study due to its compact circuits, which enables simulations over sufficiently long times to achieve the required resolution in frequency space. Specifically, we consider an antiferromagnetic quantum spin model that incorporates Dzyaloshinskii-Moriya interactions and single-ion anisotropy. The obtained 2DCS spectra exhibit distinct peaks at multiples of the magnon frequency, arising from transitions between different eigenstates of the unperturbed Hamiltonian. By comparing the one-dimensional coherent spectrum with 2DCS, we demonstrate that 2DCS provides a higher resolution of the energy spectrum. We further investigate how the quantum resources scale with the magnitude of the spin using two different binary encodings of the high-spin operators: the standard binary encoding and the Gray code. At low magnetic fields both encodings require comparable quantum resources, but at larger field strengths the Gray code is advantageous. Numerical simulations for spin models with increasing number of sites indicate a polynomial system-size scaling for quantum resources. Lastly, we compare the numerical 2DCS with experimental results on a rare-earth orthoferrite system. The observed strength of the magnonic high-harmonic generation signals in the 2DCS of the quantum high-spin model aligns well with the experimental data, showing significant improvement over the corresponding mean-field results.

Frequency combs based on magnon-skyrmion interaction in magnetic nanotubes

Abstract Within the magnonics community, there has been a lot of interests in the magnon–skyrmion interaction. Magnons and skyrmions are two intriguing phenomena in condensed matter physics, and magnetic nanotubes have emerged as a suitable platform to study their complex interactions. We show that magnon frequency combs can be induced in magnetic nanotubes by three-wave mixing between the propagating magnons and skyrmion. This study enriches our fundamental comprehension of magnon–skyrmion interactions and holds promise for developing innovative spintronic devices and applications. This frequency comb tunability and unique spectral features offer a rich platform for exploring novel avenues in magnetic nanotechnology.

Asymmetric Magnon Frequency Comb.

We theoretically show the asymmetric spin wave transmission in a coupled waveguide-skyrmion structure, where the skyrmion acts as an effective nanocavity allowing the whispering gallery modes for magnons. The asymmetry originates from the chiral spin wave mode localized in the circular skyrmion wall. By inputting two-tone excitations and mixing them in the skyrmion wall, we observe a unidirectional output magnon frequency comb propagating in the waveguide with a record number of teeth (>50). This coupled waveguide-cavity structure turns out to be a universal paradigm for generating asymmetric magnon frequency combs, where the cavity can be generalized to other magnetic structures that support the whispering gallery mode of magnons. Our results advance the understanding of the nonlinear interaction between magnons and magnetic textures and open a new pathway to exploring the asymmetric spin wave transmission and to steering the magnon frequency comb.

Spin-orbit torque manipulation of sub-terahertz magnons in antiferromagnetic α-Fe2O3

The ability to electrically manipulate antiferromagnetic magnons, essential for extending the operating speed of spintronic devices into the terahertz regime, remains a major challenge. This is because antiferromagnetic magnetism is challenging to perturb using traditional methods such as magnetic fields. Recent developments in spin-orbit torques have opened a possibility of accessing antiferromagnetic magnetic order parameters and controlling terahertz magnons, which has not been experimentally realised yet. Here, we demonstrate the electrical manipulation of sub-terahertz magnons in the α-Fe2O3/Pt antiferromagnetic heterostructure. By applying the spin-orbit torques in the heterostructure, we can modify the magnon dispersion and decrease the magnon frequency in α-Fe2O3, as detected by time-resolved magneto-optical techniques. We have found that optimal tuning occurs when the Néel vector is perpendicular to the injected spin polarisation. Our results represent a significant step towards the development of electrically tunable terahertz spintronic devices.

Design of controllable magnon frequency comb in synthetic ferrimagnets

Design of controllable magnon frequency comb in synthetic ferrimagnets

Enhanced generation of magnonic frequency combs

Enhanced generation of magnonic frequency combs

Enhancement of magnonic frequency combs by exceptional points

Enhancement of magnonic frequency combs by exceptional points

Local temperature control of magnon frequency and direction of supercurrents in a magnon Bose–Einstein condensate

The creation of temperature variations in magnetization, and hence in the frequencies of the magnon spectrum in laser-heated regions of magnetic films, is an important method for studying Bose–Einstein condensation of magnons, magnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we demonstrate analytically, numerically, and experimentally that, in addition to the magnetization variations, it is necessary to consider the connected variations of the demagnetizing field. In the case of a heat-induced local minimum of the saturation magnetization, the combination of these two effects results in a local increase in the minimum frequency value of the magnon dispersion at which the Bose–Einstein condensate emerges. As a result, a magnon supercurrent directed away from the hot region is formed.

Dissipative coupling induced UWB magnonic frequency comb generation

Magnonic frequency combs have recently attracted particular attention due to their potential impact on spin-wave science. Here, we demonstrate theoretically the generation of ultra-wideband magnonic frequency combs induced by dissipative coupling in an open cavity magnomechanical system. A broadband comb with gigahertz repetition rates is obtained in the magnonic spectrum, and a typical non-perturbation frequency-comb structure is also observed. The total width of the magnonic comb in the robust plateau region can be up to ∼400 comb lines, which is much broader and flatter than that reported in the previous works. Furthermore, when the dissipative coupling strength is further increased, the chaotic motion is predicted in the magnonic spectrum. Our results provide an in-depth understanding of nonlinear magnomechanic dynamics in open quantum systems and fundamentally broaden the research range of magnon in wider spectral regimes.

Efficient Optical Control of Magnon Dynamics in van der Waals Ferromagnets

Optical control of magnons in two-dimensional (2D) materials promises new functionalities for spintronics and magnonics in atomically thin devices. Here, we report control of magnon dynamics, using laser polarization, in a ferromagnetic van der Waals (vdW) material, Fe 3.6 Co 1.4 GeTe 2 . The magnon amplitude, frequency, and lifetime are controlled and monitored by time-resolved pump-probe spectroscopy. We show substantial (over 25%) and continuous modulation of magnon dynamics as a function of incident laser polarization. Our results suggest that the modification of the effective demagnetization field and magnetic anisotropy by the pump laser pulses with different polarizations is due to anisotropic optical absorption. This implies that pump laser pulses modify the local spin environment, which enables the launch of magnons with tunable dynamics. Our first-principles calculations confirm the anisotropic optical absorption of different crystal orientations. Our findings suggest a new route for the development of opto-spintronic or opto-magnonic devices.

Terahertz Cavity Magnon Polaritons

AbstractHybrid light–matter coupled states, or polaritons, in magnetic materials have attracted significant attention due to their potential for enabling novel applications in spintronics and quantum information processing. However, most magnon‐polariton studies in the strong coupling regime to date have been carried out for ferromagnetic materials with magnon excitations at gigahertz frequencies. Here, strong resonant photon–magnon coupling at frequencies above 1 terahertz is investigated for the first time in a prototypical room‐temperature antiferromagnetic insulator, NiO, inside a Fabry–Pérot cavity. The cavity is formed by the crystal itself with a thickness adjusted to an optimal value. Terahertz time‐domain spectroscopy measurements in magnetic fields up to 25 T reveal the evolution of the magnon frequency through Fabry–Pérot cavity modes with photon–magnon anticrossing behavior, demonstrating clear vacuum Rabi splittings exceeding the polariton linewidths. These results show that NiO is a promising platform for exploring antiferromagnetic spintronics and cavity magnonics in the terahertz frequency range.

Magnonic Frequency Comb in the Magnomechanical Resonator.

An optical frequency comb is a spectrum of optical radiation which consists of evenly spaced and phase-coherent narrow spectral lines and is initially invented in a laser for frequency metrology purposes. A direct analog of frequency combs in the magnonic systems has not been demonstrated to date. In our experiment, we generate a new magnonic frequency comb in the resonator with giant mechanical oscillations through the magnomechanical interaction. We observe the magnonic frequency comb contains up to 20 comb lines, which are separated by the mechanical frequency of 10.08MHz. The thermal effect based on the strong pump power induces the cyclic oscillation of the magnon frequency shift, which leads to a periodic oscillation of the magnonic frequency comb. Moreover, we demonstrate the stabilization and control of the frequency spacing of the magnonic frequency comb via injection locking. Our Letter lays the groundwork for magnonic frequency combs in the fields of sensing and metrology.

Discovery of ultrafast spontaneous spin switching in an antiferromagnet by femtosecond noise correlation spectroscopy

Owing to their high magnon frequencies, antiferromagnets are key materials for future high-speed spintronics. Picosecond switching of antiferromagnetic spin systems has been viewed a milestone for decades and pursued only by using ultrafast external perturbations. Here, we show that picosecond spin switching occurs spontaneously due to thermal fluctuations in the antiferromagnetic orthoferrite Sm0.7Er0.3FeO3. By analysing the correlation between the pulse-to-pulse polarisation fluctuations of two femtosecond optical probes, we extract the autocorrelation of incoherent magnon fluctuations. We observe a strong enhancement of the magnon fluctuation amplitude and the coherence time around the critical temperature of the spin reorientation transition. The spectrum shows two distinct features, one corresponding to the quasi-ferromagnetic mode and another one which has not been previously reported in pump-probe experiments. Comparison to a stochastic spin dynamics simulation reveals this new mode as smoking gun of ultrafast spontaneous spin switching within the double-well anisotropy potential.

Tutorial: Nonlinear magnonics

Nonlinear magnonics studies the nonlinear interaction between magnons and other physical platforms (phonon, photon, qubit, spin texture) to generate novel magnon states for information processing. In this Tutorial, we first introduce the nonlinear interactions of magnons in pure magnetic systems and hybrid magnon–phonon and magnon–photon systems. Then, we show how these nonlinear interactions can generate exotic magnonic phenomena. In the classical regime, we will cover the parametric excitation of magnons, bistability and multistability, and magnonic frequency comb. In the quantum regime, we will discuss the single-magnon state, Schrödinger cat state, and the entanglement and quantum steering among magnons, photons, and phonons. The applications of the hybrid magnonics systems in quantum transducer and sensing will also be presented. Finally, we look at the future development direction of nonlinear magnonics.

Nonreciprocal double-carrier frequency combs in cavity magnonics

We propose a scheme for realizing strongly nonreciprocal double-carrier frequency combs in three-mode cavity magnonic system consisting of two microwave cavities and a yttrium iron garnet sphere with magnon Kerr nonlinearity. The nonreciprocal microwave frequency comb (MWFC) and magnonic frequency comb (MFC) can be simultaneously implemented due to the asymmetrical nonlinear response in two different directions. We first show high tunability of nonreciprocal MWFC and MFC based on independent sideband in the situation of single input probe field. By properly operating the input fields, the perfect nonreciprocity of comb in a broad frequency range (nonreciprocity of number of comb) and ultrahigh isolation ratio (nonreciprocity of intensity of comb) are obtained. We prove that the tooth spacing of frequency comb can be flexibly modulated by adjusting the beat frequency between the probe field and the control field, the fraction-order comb thereby is generated, which unlocks the full potential for producing high resolution frequency comb. More importantly, it is find that the sideband mixing emerges for the situation of double input probe fields. The hybridized MWFC and the hybridized MFC further are formed, which enhances greatly nonreciprocity of fraction-order comb. These consequently give rise to the simultaneous achievement of high resolution and strong nonreciprocity of double-carrier frequency combs. Our proposal provides an effective avenue for the manipulation of the nonreciprocity and resolution of MWFC and MFC, and has potentially practical applications in precision measurement and integrated quantum technology.

Microwave-mediated magnon–atom interactions: Two-mode higher-order squeezing of two YIG spheres

We propose an efficient scheme to realize almost perfect higher-order squeezing of two YIG spheres via microwave-mediated magnon–atom interactions. It is assumed that two microwave cavity modes are coupled to two YIG spheres by the magnetic dipole interaction and a superconducting artificial atom by the electric dipole interaction, respectively. When the microwave cavity fields are tuned to be far detuned from the dressed atomic Rabi sidebands and the magnon frequencies, the coherent coupling between two magnons and the artificial atom can be established via virtual photon exchange. We find that a pair of Bogoliubov modes composed of two magnon modes are cooled to the vacuum state through the atomic engineered dissipation, resulting in an ideal two-mode higher-order squeezing state of the YIG spheres. The solid-state device may find realistic applications in high-precision measurement and quantum sensing technology.

Magnetic Field and Temperature-Dependent Brillouin Light Scattering Spectra of Magnons in Yttrium Iron Garnet.

Knowledge of the magnon responses to an external magnetic field and temperature is significant for spintronics applications. Herein, exploiting Brillouin light scattering (BLS) spectroscopy, we investigate the magnetic field and temperature dependence of the magnon frequency, line width, and intensity in yttrium iron garnet (YIG). The applied magnetic field here can effectively change the magnon frequency while maintaining the lifetime of the magnon. Specifically, we determine the temperature dependence of magnon frequency and the linear relationship between magneto-optic effects-related terms (|A(+)|2/|A(-)|2) and temperature below room temperature (RT), which can serve as a temperature sensor. Our results open an avenue to sense the temperature and the external magnetic field, including the effective magnetic field induced by the magnetic proximity effect. Furthermore, our results provide a route toward designing the operating frequency and loss of the devices, facilitating future research in spin-related applications, including magnon-based logic, memory, sensing, and thermospin devices.

Spin wave based weak magnetic field measurement at room temperature using magnonic crystal

We describe a weak magnetic field sensor operating at room temperature based on the magnonic crystal (MC). MC consisting of periodic stripes of cobalt (Co) and permalloy (Py) in one dimension is studied. The magnonic bandgaps are calculated by solving the eigenvalue problem of the Landau–Lifshitz equation using the finite element method. Magnonic bandgap frequency shifts depend upon the external magnetic field and this phenomenon is utilized for magnetic field sensing. The sensitivity characteristics of MCs with dispersion spectra in the gigahertz (GHz) frequency range are studied. It is found that the sensor’s performance gets enhanced for smaller thickness and larger periodicity. The sensitivity reaches a magnitude as large as 66.0 GHz T−1 for 10 nm thickness and 1 μm periodicity. Our analysis indicates that a limit of detection (LOD) of the order of 10−11 T can be achieved for all the geometric configurations considered in the 0–1 T range. The results are explained in terms of corresponding fundamental concepts and phenomena. Further, our simulation results show that the typical gap (e.g. 1 nm) between Co and Py stripes does not significantly affect the sensitivity of the sensor. The results also indicate that any small variation (e.g. 1 nm) in MC thickness may lead to reasonable variation in sensitivity magnitudes. Moreover, the proposed sensor’s performance is significantly superior (in terms of sensitivity, LOD, miniaturization, and material, etc) to the currently available state-of-the-art magnetometers.