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Photon-magnon coupling (PMC) integrates microwave or optical photons with magnons, aiming to exploit their distinct strengths in a unified hybrid quantum system, for potential applications in quantum information science and technology. By utilizing numerical simulations, we design a planar hybrid system comprising a hexagonal-ring resonator (HRR) and yttrium iron garnet (YIG) thin film to explore the interaction between microwave photons and magnons. The anti-crossing effects between the HRR's photon mode and the YIG's magnon modes were observed in |S21|-frequency plots under various externally applied magnetic fields. An equivalent theoretical model, based on coupled oscillators, accurately replicated the observed anti-crossing effect and provided estimates for the PMC strength. Furthermore, we explored the behavior of the photon-magnon interaction by altering the position of the YIG film on the HRR's track width, allowing for a more reliable control of the PMC strength variable within the range of 38.78 to 126.6 MHz (nearly 200%) in the planar-geometry HRR/YIG hybrid system. This study opens avenues for designing novel hybrid systems with effective control over the strength of PMC in a planar geometry. [ABSTRACT FROM AUTHOR]

In the recent years, the thermal Hall transport has risen as an important diagnosis of the physical properties of the elementary excitations in various quantum materials, especially among the Mott insulating systems where the electronic transports are often featureless. Here we review the recent development of thermal Hall effects in quantum magnets where all the relevant excitations are charge-neutral. In addition to summarizing the existing experiments, we pay a special attention to the underlying mechanisms of the thermal Hall effects in various magnetic systems, and clarify the connection between the microscopic physical variables and the emergent degrees of freedom in different quantum phases. The external magnetic field is shown to modify the intrinsic Berry curvature properties of various emergent and/or exotic quasiparticle excitations in distinct fashions for different quantum systems and quantum phases, contributing to the thermal Hall transports. These include, for example, the conventional ones like the magnons in ordered magnets, the triplons in dimerized magnets, the exotic and fractionalized quasiparticles such as the spinons and the magnetic monopoles in quantum spin liquids. We review their contribution and discuss their presence in the thermal Hall conductivity in different physical contexts. We expect this review to provide a useful guidance for the physical mechanism of the thermal Hall transports in quantum magnets. [ABSTRACT FROM AUTHOR]

The paper investigates the behavior of the magnon-magnon entanglement in a double cavity-magnon system with optical parametric amplifiers (OPA) and where both cavities are coupled by the photon tunneling process. Using the standard Langevin approach, the explicit expression is suggested for the covariance matrix describing the two magnon modes and further proved by logarithmic negativity, that the steady state of the indirectly coupled magnons is genuinely entangled. Moreover, the best parameters are obtained to achieve the magnon-magnon entanglement. It is shown that the entanglement robustness against the negative effect of the thermal bath can be enhanced by a proper choice of both the cavity-cavity coupling and the OPA gain. [ABSTRACT FROM AUTHOR]

We study the realization and transfer of entanglement in a cavity-magnon system consisting of two cavities positioned at different locations, each containing a microwave (MW) field mode and a magnon mode of the yttrium iron garnet (YIG) sphere. The magnon mode is coupled to the MW cavity mode via a linear beam splitter interaction. As reported by Benrass et al. (Int. J. Mod. Phys. B 36, 2250036, 2022), it has been shown that the logarithmic negativity remains nonzero in the coexistence zone, illustrating why the latter includes entangled states. Additionally, a novel method for quantifying entanglement in quantum systems based on purity was introduced. Based on this, the main objective of this work is to examine how purity can be taken as evidence for the mixedness and entanglement that characterize the cavity-cavity and the magnon-magnon subsystems. A comparison of the entanglement behaviors with those obtained for purity under the influence of different parameters demonstrates that this resembles the use of purity as a feature and a quantification of the degree of entanglement in the two-mode symmetric state. [ABSTRACT FROM AUTHOR]

The thermal Hall effect (THE) is an important experimental probe of band topology and elementary excitations. Here, a large thermal Hall angle (THA) κxy/κxx ≈ 7 × 10−3 discovered so far in ferrimagnetic spinel FeCr2S4 and a large thermal Hall conductivity (κxy) discovered first in spinel structure and reaching a magnitude of κxy≈1.8×10−2WK−1m−1$\kappa _{xy} \approx 1.8 \times 10^{-2} \rm {W K^{-1} m^{-1}}$ at 50 K with a small magnetic field of 0.1 T are reported. These results suggest the emergence of nontrivial topological excitations in FeCr2S4. A large THA in spin caloritronics devices means that a small number of excitations can produce a large transverse signal. FeCr2S4 is therefore a potential platform for spintronics‐magnonics applications, and may enhance the knowledge of the thermal Hall effect. [ABSTRACT FROM AUTHOR]

We report a theory of thermal spin pumping into proximity magnets under a transverse-bias-driven heat flow of magnons in magnetic films when the dipolar coupling to the magnetic gate is tuned to be "chiral". While there is no rectification of the magnon current in the film, we predict that chirality diverts a large percentage (50% for perfect chirality) of it into the gate. This transverse thermal spin pumping effect can be controlled by rotating the film magnetization and may help manage the heat flow in future magnonic circuits. [ABSTRACT FROM AUTHOR]

The thickness of the magnetic ( t Fe ) and non-magnetic ( t Pt ) layers have an effect on the magnetic exchange anisotropy property, which is related to the evolution of the mixture's magnetization, as we will explore in this study. We concentrate on the existence of two distinct "classical" and "quantum" magnons populations that were both generated at (T ≃ T c 3) and were consistently connected to the occurrence of a spin reorientation transition (SRT). The existence of this "mixture" is confirmed by the extremely high agreement between the calculated results M cal z (T , t , h) and the observed values M exp z (T , t , h) . Using this information, we were able to determine the values of the various properties of the studied system, (Fe / Pt) , including the exchange integrals (J ‖ , J ⊥) , the surface anisotropy α , the magnetocrystalline anisotropy Δ , the critical transition temperature T c , the magnon creation gap E g , the lifetime of the created magnons τ and the spin constant B 3 / 2 . [ABSTRACT FROM AUTHOR]

We present a high-performance scheme of soft quantum control to deterministically generate entangled NOON states between two magnon modes. A superconducting qubit is considered as a data bus coupled to two magnon modes and a circuit resonator that accounts for providing an N-photon Fock state. Assisted by the Floquet engineering, effective couplings among the photon mode in the resonator and two magnon modes are constructed and can induce a chiral Fock-state transfer from the photon mode to one magnon mode, for which the magnonic Fock-state receiver mode is dependent of the qubit state. Therefore, a superposed qubit state can exactly lead to a magnonic NOON state. Compared with the recent scheme of generating magnonic NOON states (Qi and Jing in Phys Rev A 107:013702, 2023) that uses constant effective couplings, the present scheme designs Gaussian-type soft control of effective couplings, which observably improves the fidelity and robustness of generating the magnonic NOON state. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a system composed of two spatially separated cavities, each with a magnon mode of a yttrium iron garnet (YIG) sphere coupled to a microwave (MW) cavity and phonon modes, respectively, via linear beam splitter and magnetostrictive interactions. In addition, two-mode squeezed vacuum fields drive the two cavities. We investigate and compare the behavior of three nonclassicality indicators in two subsystems (i.e., magnon–magnon and phonon–phonon) under the influences of the temperature, the cavity–magnon damping rate, and the magnomechanical coupling rate. We use the entanglement of formation (EoF) to measure the degree of entanglement, the Gaussian quantum discord (GQD) to characterize the quantum correlations beyond entanglement and Gaussian quantum coherence (GQC) to quantify coherence. Considering that the quantifiers share the same entropic definition, we compare the three quantifiers and test the validity of the hypothesis that quantum states with nonzero discord are inherently entangled. We find, on the one hand, that both GQC and GQD exhibit freezing behavior and that they are more robust to the decoherence effect than the EoF. On the other hand, the EoF and the GQD are always upper bounded by GQC, and there is no simple dominance relationship between EoF and GQD; hence these two quantifiers should not be compared. The effect of other parameters is also discussed in detail. [ABSTRACT FROM AUTHOR]

Magnonic mode interconversion has paved the way for the integration of various developed magnonic functionalities, such as logic gates, switches, and multiplexers; however, it is limited by intrinsic magnetic damping. Therefore, this study proposes a potential amplification method to integrate spin-waves into magnonic circuits. The phase-matching conditions were tuned by introducing a feedback-ring structure. The results of microfocused Brillouin light scattering spectroscopy and micromagnetic simulations demonstrate the effectiveness of the spin-wave enhancement of feedback-ring structure. Consequently, spin-wave enhancement preserving phase information can be developed to realize integrated magnonic circuits. [ABSTRACT FROM AUTHOR]

We propose to realize bipartite and tripartite entanglements transfer in a cavity magnomechanical system consisting of a microwave cavity with an yttrium iron garnet (YIG) sphere and a silicon-nitride membrane in it. The initial magnon–YIG phonon entanglement and photon-membrane phonon entanglement caused by the magnetostrictive interaction and the optomechanical interaction can be effectively transferred to magnon–membrane phonon entanglement and photon–YIG phonon entanglement. Photon–magnon–YIG phonon and photon–magnon–membrane phonon entanglements can also be realized in the system. These two types of tripartite entanglements can be easily transferred from one type to the other by adjusting the detuning or dissipation ratio. Moreover, the bipartite and tripartite entanglements and their transfer are all robust against temperature. Furthermore, by introducing supermodes formed by the photon and magnon modes, we find that the entanglement between the two mechanical modes can be obtained under the condition of an extremely low temperature. And the effective detuning region of the YIG phonon-membrane phonon entanglement is complementary to the detuning regions of other bipartite entanglements. Our results indicate that the combination of cavity magnomechanical and optomechanical systems could provide more flexible controllability of bipartite and tripartite entanglements and their transfer and could serve as a potential quantum interface among microwave, magnon, and mechanical systems.

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.

We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities. [ABSTRACT FROM AUTHOR]

Growing concentration on the novel information processing technology and low‐cost, flexible materials make the spintronics and organic materials appealing for the future interdisciplinary investigations. Organic spintronics, in this context, has arisen and witnessed great advances during the past two decades owing to the continuous innovative exploitation of the charge‐contained spin polarized current. Albeit with such inspiring facts, charge‐absent spin angular momentum flow, namely pure spin currents (PSCs) are less probed in organic functional solids. In this review, the past exploring journey of PSC phenomenon in organic materials are retrospected, including non‐magnetic semiconductors and molecular magnets. Starting with the basic concepts and the generation mechanism for PSC, the representative experimental observations of PSC in the organic‐based networks are subsequently demonstrated and summarized, by accompanying explicit discussion over the propagating mechanism of net spin itself in the organic media. Finally, future perspectives on PSC in organic materials are illustrated mainly from the material point of view, including single molecule magnets, complexes for the organic ligands framework as well as the lanthanide metal complexes, organic radicals, and the emerging 2D organic magnets. [ABSTRACT FROM AUTHOR]

This work reports on the stationary evolution of three different kinds of quantum correlations between two distant magnon modes. The system at hand consists of two spatially separated cavities, where each cavity has a microwave (MW) cavity and a magnon mode. The two cavities are coupled to each other via the photon-tunneling process, and both are exposed to the output field of a squeezed vacuum MW fields source. By calculating the covariance matrix fully describing the state of the two magnon modes, we give the explicit expressions of the measures of correlations defined via the Rényi-2 entropy, i.e. the Gaussian quantum steering , Gaussian Rényi-2 entanglement E R and Gaussian Rényi-2 mutual information I R . We find that, the quantum steering is always upper bounded by the entanglement, which is in turn always upper bounded by half of the total correlations. The obtained results are consistent with the hierarchical Rényi-2 quantum correlations established in [L. Lami, C. Hirche, G. Adesso and A. Winter, Phys. Rev. Lett. 117, 220502 (2016)], i.e. they fulfill the hierarchical inequality (1 / 2) I R ≥ E R ≥ . The influences of the squeezing parameter, the environmental temperature, the cavity–magnon coupling and the cavity–cavity coupling on the correlations are studied in detail. [ABSTRACT FROM AUTHOR]

In this paper, without using an external magnetic field, ferromagnetism on diluted InFeSb magnetic semiconductors is studied up to 317.65 K. The spin-wave model that the Heisenberg Hamiltonian translates into in the system has been developed using the green function formalism and the Holstein–Primakoff transformation estimate. The numbers of magnons, dispersion, Curie temperature, susceptibility, and specific heat capacity of the system have all been determined using the established model. The findings demonstrate that the ferromagnetic in In0.893Fe0.107Sb has a Curie temperature that is significantly higher than those found in prior investigations (317.65 K).

Abstract Growing concentration on the novel information processing technology and low‐cost, flexible materials make the spintronics and organic materials appealing for the future interdisciplinary investigations. Organic spintronics, in this context, has arisen and witnessed great advances during the past two decades owing to the continuous innovative exploitation of the charge‐contained spin polarized current. Albeit with such inspiring facts, charge‐absent spin angular momentum flow, namely pure spin currents (PSCs) are less probed in organic functional solids. In this review, the past exploring journey of PSC phenomenon in organic materials are retrospected, including non‐magnetic semiconductors and molecular magnets. Starting with the basic concepts and the generation mechanism for PSC, the representative experimental observations of PSC in the organic‐based networks are subsequently demonstrated and summarized, by accompanying explicit discussion over the propagating mechanism of net spin itself in the organic media. Finally, future perspectives on PSC in organic materials are illustrated mainly from the material point of view, including single molecule magnets, complexes for the organic ligands framework as well as the lanthanide metal complexes, organic radicals, and the emerging 2D organic magnets.

The tunability of magnons enables their interaction with various other quantum excitations, including photons, paving the route for novel hybrid quantum systems. Here, we study magnon-photon coupling using a high-quality factor split-ring resonator and single-crystal yttrium iron garnet (YIG) sphere at room temperature. We investigate the dependence of the coupling strength on the size of the sphere and find that the coupling is stronger for spheres with a larger diameter as predicted by theory. Furthermore, we demonstrate strong magnon-photon coupling by varying the position of the YIG sphere within the resonator. Our experimental results reveal the expected correlation between the coupling strength and the rf magnetic field. These findings demonstrate the control of coherent magnon-photon coupling through the theoretically predicted square-root dependence on the spin density in the ferromagnetic medium and the magnetic dipolar interaction in a planar resonator.

In this paper, we consider a cavity magnomechanical system composed of a microwave (MW) cavity, magnon, and phonon modes, where the magnon is coupled, respectively, to the MW cavity and phonon through both the magnetic-dipole and magnomechanical interactions. We demonstrate that the flux-driven Josephson parametric amplifier with a nonlinear gain is crucial in creating the squeezed states of the magnon and phonon modes. We show that, by the cavity-magnon state-swap interaction, the magnons can be completed in a squeezed state, and that the phonons can also be squeezed by driving the magnons through a strong red-detuned MW field. Essentially, our system reveals a squeezing transfer from cavity photons to magnons and then to phonons. The influence of physical and environmental parameters on the degree of squeezing is widely explored. [ABSTRACT FROM AUTHOR]

Coupled mode theory predicts that the long-distance coupling between two distant harmonic oscillators is in the weak coupling regime. However, a recent experimental measurement observed strong coupling of magnon and critically-driven photon with a distance of over two meters. To explain the discrepancy between theory and experiment, we study long-distance coupling of magnon and photon mediated by a multi-mode waveguide. Our results show that strong coupling is achieved only when both critical coupling and multi-mode waveguide are involved. The former reduces the damping while the latter enhances the coupling strength by increasing the pathways of coupling magnon and photon. Our theory and results pave the way for understanding the long-distance coherence and designing the magnon-based distributed quantum networks. • Long-distance strong coupling between magnon and photon is obtained. • Strong coupling is due to both multi-mode waveguide and critical coupling. • 2 pi-period is obtained as the YIG-cavity distance increases. • Higher-order propagation mode may be related to the TM0 surface mode. • The physics in this work can be tested by varying the thickness of waveguide in future experiment. [ABSTRACT FROM AUTHOR]

Hybrid quantum systems have attracted much attention due to the fact that they combine the advantages of different physical subsystems. Cavity QED (cavity quantum electrodynamics) with magnons is a hybrid quantum systems that combines a YIG (Yttrium Iron Garnet) sphere and a 3D (three-dimensional) rectangular microwave cavity. Based on this hybrid photon-magnon system, we obtain an approximate analytic solution by the RWA (rotating wave approximation) with an ingenious transformation. After skillfully diagonalizing the Hamiltonian, we show that the Kerr-nonlinearity interactions could yield a negativity value of the Wigner function, periodic quadrature squeezing effects, antibunching property, and field nonclassicality in the magnon. Our work may stimulate the study of nonclassicality of photon-magnon coupling systems and its potential applications in quantum information processing. [ABSTRACT FROM AUTHOR]

Spin transport and the associated spin torque effects in antiferromagnets (AFMs) are scientifically interesting but have remained elusive due to the varied observations of spin transport in AFMs. This study revisits the role of a global Néel order in nickel oxide (NiO) facilitated through a spin-orbit torque (SOT) and examines the enhanced SOT efficiency in a heavy metal (W)/AFM (NiO)/ferromagnet (FM, CoFeB) trilayer with varying NiO thicknesses ranging from 1 to 5 nm. At the as-grown state, the Néel order of NiO is randomly oriented due to the polycrystalline nature of the film structure, leading to increased spin absorption and blocking spin transport from the adjacent W layer. When the spin current amplitude exceeds a threshold value, SOT enables reorientation of the Néel order in NiO to an equilibrium state, forming a global Néel order aligned with the applied current. This long-range Néel order reduces spin absorption and enhances spin transport through NiO, hence boosting the SOT efficiency in the adjacent CoFeB layer. X-ray magnetic linear dichroism spectroscopy and rewritable Néel order reorientation experiments in a device with orthogonal geometry confirmed the strong correlation between the global Néel order facilitation and the boosted SOT efficiency, which is enhanced larger than 4-fold for both damping- and field-like torques in the trilayer with 5 nm NiO. This study not only reveals the strong correlation between globally facilitated Néel order and spin transport in NiO but also offers a promising manner to promote AFM-based SOT devices toward energy-efficient computing technology.

The dynamics of magnetization is important in spintronics, where the coupling between phonon and magnon attracts much attention. In this work, we study the angular dependence of the coupling between longitudinal-wave phonon and magnon. We investigated the magnetization dynamics using the time-resolved magneto-optical Kerr effect, which allows measuring spin-wave resonances and the magnetic echo signal. The frequency, mode number, and amplitude of the spin-wave resonance change with the out-of-plane angle of the external magnetic field. The amplitude of the magnetic echo signal caused by the strain pulse also changes with the angle. We calculate these angular dependences based on the Landau–Lifshitz–Gilbert equation and find that the angles of the external field and magnetic moment are important factors for the phonon–magnon coupling when phonon propagates in the thickness direction under the out-of-plane magnetic field. [ABSTRACT FROM AUTHOR]

We have extensively studied the phonon, magnon and magnetic properties of copper (Cu)‐doped nanocrystalline nickel(II) oxide (NiO) using room‐temperature Raman spectroscopy. The required nanomaterials were synthesized using a simple sol–gel method. The phonon modes of NiO nanoparticles have been observed in a large background of magnon excitations, and the wavenumbers of phonon modes were deviated from the theoretical predictions due to the phonon–magnon interaction. The variations of magnon excitations with the Cu doping concentrations were investigated based on reduced spin correlation length and superexchange interaction. The two‐magnon (2M) excitations were suppressed and blue shifted with Cu doping concentration indicating the variations in the magnetic behaviour. The modification of antiferromagnetic nature and the formation of multiphase magnetic properties of NiO nanoparticles were investigated using a vibrating sample magnetometer (VSM) and discussed in detail. The variations in the phonon and magnon excitations can be used to probe the magnetic nature and spintronic applications of NiO nanoparticles. [ABSTRACT FROM AUTHOR]

Spintronics and quantum information science are two promising candidates for innovating information processing technologies. The combination of these two fields enables us to build solid-state platforms for studying quantum phenomena and for realizing multi-functional quantum tasks. For a long time, however, the intersection of these two fields was limited due to the distinct properties of the classical magnetization, that is manipulated in spintronics, and quantum bits, that are utilized in quantum information science. This situation has changed significantly over the last few years because of the remarkable progress in coding and processing information using magnons. On the other hand, significant advances in understanding the entanglement of quasi-particles and in designing high-quality qubits and photonic cavities for quantum information processing provide physical platforms to integrate magnons with quantum systems. From these endeavours, the highly interdisciplinary field of quantum magnonics emerges, which combines spintronics, quantum optics and quantum information science. Here, we give an overview of the recent developments concerning the quantum states of magnons and their hybridization with mature quantum platforms. First, we review the basic concepts of magnons and quantum entanglement and discuss the generation and manipulation of quantum states of magnons, such as single-magnon states, squeezed states and quantum many-body states including Bose–Einstein condensation and the resulting spin superfluidity. We discuss how magnonic systems can be integrated and entangled with quantum platforms including cavity photons, superconducting qubits, nitrogen-vacancy centers, and phonons for coherent information transfer and collaborative information processing. The implications of these hybrid quantum systems for non-Hermitian physics and parity-time symmetry are highlighted, together with applications in quantum memories and high-precision measurements. Finally, we present an outlook on some of the challenges and opportunities in quantum magnonics. [ABSTRACT FROM AUTHOR]

Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors, which covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with the Boolean digital data, unconventional approaches, such as neuromorphic computing, and the progress toward magnon-based quantum computing. This article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of current challenges and the outlook of further development for each research direction. [ABSTRACT FROM AUTHOR]

The magnonic frequency comb (MFC) induced by magnon–skyrmion interaction not only exhibits interesting nonlinear physics but also can be used to detect magnetic solitons and defects in ferromagnetic materials. Modulating the tooth spacing of MFC is crucial for its application in magnon‐based devices. Herein, it is demonstrated from micromagnetic simulations that the MFC tooth spacing of ferromagnetic thin film can be effectively modulated by a biaxial in‐plane strain via magnetoelastic coupling. It is found that the MFC tooth spacing increases with the increase of compressive strain and decreases with the increase of tensile strain. The strain modulation of MFC tooth spacing stems from the strain‐dependent magnetocrystalline anisotropy. The detailed energy analysis shows that the larger the tooth spacing is, the higher the exchange energy is, and the lower the magnetoelastic and anisotropy energies are. In addition, when the biaxial in‐plane strain becomes nonequally axial (or anisotropic), the tooth spacing becomes smaller, accompanied by a decrease in the magnetoelastic energy. The results of this study suggest an effective way to modulate the tooth spacing of MFC by strain, which may hold a promise for application in tunable magnon‐based devices. [ABSTRACT FROM AUTHOR]

We develop a theory for the dynamics of a magnon on top of a domain wall in a ferromagnetic nanotube. Due to the geometry of the sample, domain walls are classified by the Skyrmion charge which counts the winding number of magnetic textures. The domain wall with a non-zero Skyrmion charge generates an emergent magnetic field for magnons, which exerts the Lorentz force on moving magnons and thereby deflects their trajectories. This deflection is manifested as the generation of the finite orbital angular momentum of the magnon that traverses the domain wall. We obtain exact solutions for the magnon on top of the Skyrmion-textured domain wall and also their scattering properties with the domain wall with the aid of supersymmetric quantum mechanics. We show that there is a critical wavenumber for the total reflection of magnons and it is discretized by the Skyrmion charge of the domain wall. Our results show that the orbital angular momenta of magnetic textures and magnons can be intertwined in a curved geometry.

We report the existence of entangled steady-states in bipartite quantum magnonic systems at elevated temperatures. We consider dissipative dynamics of two magnon modes in a bipartite antiferromagnet, subjected to interaction with a phonon mode and an external rotating magnetic field. To quantify the bipartite magnon–magnon entanglement, we use entanglement negativity and compute its dependence on temperature and magnetic field. We provide evidence that the coupling between magnon and phonon modes is necessary for the entanglement, and that, for any given phonon frequency and magnon–phonon coupling rate, there are always ranges of the magnetic field amplitudes and frequencies for which magnon–magnon entanglement persists at room temperature.

van der Waals (vdW) magnets have rapidly emerged as a fertile playground for fundamental physics and exciting applications. Despite the impressive developments over the past few years, technical limitations pose a severe challenge to many other potential breakthroughs. High on the list is the lack of suitable experimental tools for studying spin dynamics on atomically thin samples. Here, Raman scattering techniques are employed to directly observe the low-lying magnon (∼1 meV) even in bilayer NiPS 3 . The advantage is that it offers excellent energy resolutions far better on low-energy sides than most inelastic neutron spectrometers can offer. More importantly, with appropriate theoretical analysis, the polarization dependence of the Raman scattering by those low-lying magnons also provides otherwise hidden information on the dominant spin-exchange scattering paths for different magnons. By comparing with high-resolution inelastic neutron scattering data, these low-energy Raman modes are confirmed to be indeed of magnon origin. Because of the different scattering mechanisms involved in inelastic neutron and Raman scattering, this information is fundamental in pinning down the final spin Hamiltonian. This work demonstrates the capability of Raman spectroscopy to probe the genuine two-dimensional spin dynamics in atomically thin vdW magnets, which can provide insights that are obscured in bulk spin dynamics.

We propose a method to generate magnetic skyrmions by focusing spin waves totally reflected by a curved film edge. The edge contour is derived to be parabolic and frequency-independent based on the identical magnonic path length principle. We performed micromagnetic simulations to verify our theoretical design. Under proper conditions, the reflected spin waves first converge at the focal point with the enhanced intensity leading to the emergence of magnetic droplets, which are then converted to magnetic skyrmion accompanied by a change in the topological charge. We numerically obtain the phase diagram of skyrmion generation with respect to the amplitude and frequency of the driving field. Our finding would be helpful for the design of spintronic devices combining the advantage of skyrmionics and magnonics.

Hybrid quantum systems have attracted much attention due to the fact that they combine the advantages of different physical subsystems. Cavity QED (cavity quantum electrodynamics) with magnons is a hybrid quantum systems that combines a YIG (Yttrium Iron Garnet) sphere and a 3D (three-dimensional) rectangular microwave cavity. Based on this hybrid photon-magnon system, we obtain an approximate analytic solution by the RWA (rotating wave approximation) with an ingenious transformation. After skillfully diagonalizing the Hamiltonian, we show that the Kerr-nonlinearity interactions could yield a negativity value of the Wigner function, periodic quadrature squeezing effects, antibunching property, and field nonclassicality in the magnon. Our work may stimulate the study of nonclassicality of photon-magnon coupling systems and its potential applications in quantum information processing.

This review presents the results about spin caloritronics obtained at the Department of Low Temperature Physics of the Kharkiv National University from 2017 to 2019 years. Several new directions in magneto-electronics: spintronics, spin caloritronics and magnonics, which emerged with the aim to reduce the energy dissipation in devices of usual semiconductor microelectronics, are discussed. Spintronic devices hold the promise of faster switching speeds, less total energy consumption, and higher density of circuit elements, lowering the heat production per switching element. Then the main results of the four papers published in Physical Review B are discussed: nonlinear relaxation between magnons and phonons in insulating ferromagnets; role of magnons and the size effect in heat transport through an insulating ferromagnet-insulator interface; spin Seebeck effect and phonon energy transfer in heterostructures containing layers of normal metal and ferroinsulator; temperature dependence of the magnon-phonon energy relaxation time in a ferromagnet insulator. [ABSTRACT FROM AUTHOR]

The frequencies of low-lying electronic excitations in the quasi-one-dimensional antiferromagnet CsFeCl3 · 2H2O were determined by Raman spectroscopy. The lowest of them (57 cm−1) was attributed to the magnon-like excitation of the chain of Ising spins of paramagnetic Fe2+ ions. And the next one (77 cm−1) can most likely be attributed to the exciton-like one, associated with the electronic transition to the lower level of the excited orbital quasi-doublet dzx, dzy split by the spin-orbit interaction. Investigations of the splittings and shifts of Raman lines in an external magnetic field allowed us to estimate the values of the magnetic moments of the sublattices in the ground state and to determine their spatial orientation relative to the crystallographic directions. [ABSTRACT FROM AUTHOR]

The spontaneous magnetic orders arising in ferro-, ferri- and antiferromagnets stem from various magnetic interactions. Depending on the interplay and competition among the Heisenberg exchange interaction, Dzyaloshinskii–Moriya exchange interaction, magnetic dipolar interaction and crystal anisotropies, a great variety of magnetic textures may be stabilized, such as magnetic domain walls, vortices, Skyrmions and spiral helical structures. While each of these spin textures responds to external forces in a specific manner with characteristic resonance frequencies, they also interact with magnons, the fundamental collective excitation of the magnetic order, which can propagate in magnetic materials free of charge transport and therefore with low energy dissipation. Recent theories and experiments found that the interplay between spin waves and magnetic textures is particularly interesting and rich in physics. In this review, we introduce and discuss the theoretical framework of magnons living on a magnetic texture background, as well as recent experimental progress in the manipulation of magnons via magnetic textures. The flexibility and reconfigurability of magnetic textures are discussed regarding the potential for applications in information processing schemes based on magnons. [ABSTRACT FROM AUTHOR]

The generation and manipulation of strong entanglement and Einstein-Podolsky-Rosen (EPR) steering in macroscopic systems are outstanding challenges in modern physics. Especially, the observation of asymmetric EPR steering is important for both its fundamental role in interpreting the nature of quantum mechanics and its application as resource for the tasks where the levels of trust at different parties are highly asymmetric. Here, we study the entanglement and EPR steering between two macroscopic magnons in a hybrid ferrimagnet—light system. In the absence of light, the two types of magnons on the two sublattices can be entangled, but no quantum steering occurs when they are damped with the same rates. In the presence of the cavity field, the entanglement can be significantly enhanced, and strong two-way asymmetric quantum steering appears between two magnons with equal dissipation. This is very different from the conventional protocols to produce asymmetric steering by imposing additional unbalanced losses or noises on the two parties at the cost of reducing steerability. The essential physics is well understood by the unbalanced population of acoustic and optical magnons under the cooling effect of cavity photons. Our finding may provide a novel platform to manipulate the quantum steering and the detection of bi-party steering provides a knob to probe the magnetic damping on each sublattice of a magnet. [ABSTRACT FROM AUTHOR]

We report a theoretical study on the effect of the exchange coupling on magnon propagation in a waveguide, composed of a dipole-coupled nanometric magnetic cluster chain and a few additional clusters near the chain. We show that an appropriate choice of the exchange coupling constant J or the geometrical/magnetic parameters of the structure can lead either to narrow dips or to narrow peaks in the transmission spectrum of magnons along the chain. The phase of the transmission amplitude, the state phase shift and the variation of the density of states are also discussed as a function of frequency for different values of J. The effect of attenuation on the transmission spectra is also discussed. The results are obtained by means of the Green's function technique. The presented study could be useful for constructing the selecting or rejecting magnon filters. [ABSTRACT FROM AUTHOR]

A theoretical study on the interplay of frustrated skyrmion and magnons should reveal new physics and future experiment designs. In this study, we investigate the magnon-driven dynamics of frustrated skyrmion in synthetic antiferromagnets based on micromagnetic simulations, focusing on the effect of skyrmion helicity oscillation. The oscillation speed and Hall angle of the frustrated skyrmion depending on the magnon intensity and damping constant are simulated, which demonstrates that the skyrmion helicity oscillation effectively suppresses Hall motion. The elastic scattering theory reveals that the helicity oscillation affects the scattering cross-section of injected magnons, which in turn effectively modulates the skyrmion Hall motion. This study provides a comprehensive understanding of magnon-skyrmion scattering in frustrated magnets, thus benefiting future spintronic and magnonic applications.