Search

In this work, we present the results of a systematic experimental study of linear and parametric spin wave resonant excitation accompanied by spin currents (spin pumping) in a multifrequency composite bulk acoustic wave resonator with a ZnO-YIG-GGG-YIG/Pt structure. The features of magnetic dynamics excitation in YIG films due to magnetoelastic coupling with acoustic thickness modes of various polarizations are studied. Acoustic spin waves and spin pumping are detected by simultaneous frequency-field mapping of the inverse spin Hall effect voltage and the resonant frequencies of thickness extensional modes. In the parametric range of frequencies and fields, acoustic spin pumping induced by both shear and longitudinal polarization modes was observed. Linear acoustic spin waves are excited only by shear thickness extensional modes because longitudinal acoustic waves do not couple with the magnetic subsystem in linear regime. [ABSTRACT FROM AUTHOR]

Employing short laser pulses with a duration below 100 fs for changing magnetic state of magnetically-ordered media has developed into a distinct branch of magnetism femtomagnetism which aims at controlling magnetization at ultimately short timescales. Among plethora of femtomagnetic phenomena, there is a class related to impact of femtosecond pulses on magnetic anisotropy of materials and nanostructures which defines orientation of magnetization, magnetic resonance frequencies and spin waves propagation. We present a review of main experimental results obtained in this field. We consider basic mechanisms responsible for a laser-induced change of various anisotropy types: magnetocrystalline, magnetoelastic, interfacial, shape anisotropy, and discuss specifics of these processes in magnetic metals and dielectrics. We consider several examples and describe features of magnetic anisotropy changes resulting from ultrafast laser-induced heating, impact of laser-induced dynamic and quasistatic strains and resonant excitation of electronic states. We also discuss perspectives of employing various mechanisms of laser-induced magnetic anisotropy change for enabling processes prospective for developing devices. We consider precessional magnetization switching for opto-magnetic information recording, generation of high-frequency strongly localized magnetic excitations and fields for magnetic nanotomography and hybrid magnonics, as well as controlling spin waves propagation for optically-reconfigurable magnonics. We further discuss opportunities which open up in studies of ultrafast magnetic anisotropy changes because of using short laser pulses in infrared and terahertz ranges. [ABSTRACT FROM AUTHOR]

Devices for performing computation and logic operations with low‐energy consumption are of key importance for environmentally friendly data processing and information technology. Here, a design for magnetic elements that use excess heat to perform logic operations is presented. The basic information channel is coupled non‐conductive magnetic stripes with a normal metal spacer. The thermal information signal is embodied in magnetic excitations and it can be transported, locally enhanced, and controllably steered by virtue of charge current pulses in the spacer. Functionality of essential thermal logic gates is demonstrated by material‐specific simulations. The operation principle takes advantage of the special material architecture with a balanced gain/loss mechanism for magnetic excitation which renders the circuit parity‐time symmetric with exceptional points tunable by the current strength in the spacer. Heat flow at these points can be enhanced, be non‐reciprocal, or may oscillate between the information channels enabling controlled thermal diode and thermal gate operations. The findings point to a new route for exploiting heat for useful work on the nanoscale. [ABSTRACT FROM AUTHOR]

Physical reservoir computing, which is a promising method for the implementation of highly efficient artificial intelligence devices, requires a physical system with nonlinearity, fading memory, and the ability to map in high dimensions. Although it is expected that spin wave interference can perform as highly efficient reservoir computing in some micromagnetic simulations, there has been no experimental verification to date. Herein, reservoir computing is demonstrated that utilizes multidetected nonlinear spin wave interference in an yttrium‐iron‐garnet single crystal. The subject computing system achieves excellent performance when used for hand‐written digit recognition, second‐order nonlinear dynamical tasks, and nonlinear autoregressive moving average (NARMA). It is of particular note that normalized mean square errors for NARMA2 and second‐order nonlinear dynamical tasks are 1.81 × 10−2 and 8.37 × 10−5, respectively, which are the lowest figures for any experimental physical reservoir so far reported. Said high performance is achieved with higher nonlinearity and the large memory capacity of interfered spin wave multidetection. [ABSTRACT FROM AUTHOR]

We report an inelastic neutron scattering study of candidate multiferroic ErFeO 3 , a compound that has been previously reported to have three different magnetic states and undergoes signatures of Fe 3 + − Er 3 + cooperative coupling. The spectrum at low energy transfer is dominated by excitations of the Er 3 + character, even above the Er 3 + antiferromagnetic ordering temperature of 4.5 K. In addition, a crystalline electric field excitation at 6 meV exhibits additional energy splitting upon cooling through 4.5 K with mode-dependent polarization. This indicates different moment directions for these modes, an interesting consequence of C y ordering of the Er 3 + moments. [ABSTRACT FROM AUTHOR]

Spin wave dynamics form the foundation of spin-torque oscillator (STO) modulation. In addition to the uniform spin wave mode with wave vector k = 0, multiple spin wave modes with different wave vectors and frequencies coexist in the nanoscale STO. To characterize these spin wave modes and the interactions between them, the distribution and evolution of spin wave intensity in k space need to be investigated together with spin wave dispersion of the individual mode, stressing energy degeneracy. To this end, using micromagnetic simulation, we studied the dynamics of the discrete spin wave modes in a nanoscale STO with structure enhancing spin wave propagation. Simulation using the object oriented micromagnetic framework demonstrated that although they were generated with different spin currents, spin wave modes evolved similarly in k space, according to the wave vector. Furthermore, magnetization pinning at the corners of yttrium iron garnet led to two-magnon scattering. This interaction affects spin wave dynamics in two ways: multivalued dispersion occurs with two-magnon scattering and the uniform mode can become weaker than the near-uniform modes (spin wave modes with wave vector close to zero) in the strong excitation region. The latter phenomenon is supported by the results of studies on the spin wave dispersion of the individual mode, which demonstrate the energy degeneracy between the uniform mode and the near-uniform modes. [ABSTRACT FROM AUTHOR]

We study the quantum phase transitions of frustrated antiferromagnetic Heisenberg spin-1 systems on the 3/4 and 3/5 skewed two leg ladder geometries. These systems can be viewed as arising by periodically removing rung bonds from a zigzag ladder. We find that in large systems, the ground state (gs) of the 3/4 ladder switches from a singlet to a magnetic state for J 1 ≥ 1.82 ; the gs spin corresponds to the ferromagnetic alignment of effective S = 2 objects on each unit cell. The gs of antiferromagnetic exchange Heisenberg spin-1 system on a 3/5 skewed ladder is highly frustrated and has spiral spin arrangements. The amplitude of the spin density wave in the 3/5 ladder is significantly larger compared to that in the magnetic state of the 3/4 ladder. The gs of the system switches between singlet state and low spin magnetic states multiple times on tuning J 1 in a finite size system. The switching pattern is nonmonotonic as a function of J 1 and depends on the system size. It appears to be the consequence of a higher J 1 favoring a higher spin magnetic state and the finite system favoring a standing spin wave. For some specific parameter values, the magnetic gs in the 3/5 system is doubly degenerate in two different mirror symmetry subspaces. This degeneracy leads to spontaneous spin-parity and mirror symmetry breaking, giving rise to spin current in the gs of the system. [ABSTRACT FROM AUTHOR]

Using artificially controlled ferromagnet (FM)–semiconductor (SC) interfaces, we study the decay of the nonlocal spin signals with increasing temperature in SC-based lateral spin-valve devices. When more than five atomic layers of Fe are inserted at the FM/SC interfaces, the temperature-dependent spin injection/detection efficiency (P inj / det ) can be interpreted in terms of the T 3 2 law, meaning a model of the thermally excited spin waves in the FM electrodes. For the FM/SC interfaces with the insufficient insertion of Fe atomic layers, on the other hand, the decay of P inj / det is more rapid than the T 3 2 curve. Using magneto-optical Kerr effect measurements, we find that more than five atomic layers of Fe inserted between FM and SC enable us to enhance the ferromagnetic nature of the FM/SC heterointerfaces. Thus, the ferromagnetism in the ultra-thin FM layer just on top of SC is strongly related to the temperature-dependent nonlocal spin transport in SC-based lateral spin-valve devices. We propose that the sufficient ferromagnetism near the FM/SC interface is essential for high-performance FM–SC hybrid devices above room temperature. [ABSTRACT FROM AUTHOR]

In the last decades, collinear magnetic insulating systems have emerged as promising energy-saving information carriers. Their elementary collective spin excitations, i.e., magnons, can propagate for long distances bypassing the Joule heating effects that arise from electron scattering in metal-based devices. This Tutorial article provides an introduction to theoretical and experimental advances in the study of magnonics in collinear magnetic insulating systems. We start by outlining the quantum theory of spin waves in ferromagnetic and antiferromagnetic systems, and we discuss their quantum statistics. We review the phenomenology of spin and heat transport of the coupled coherent and incoherent spin dynamics and the interplay between magnetic excitations and lattice degrees of freedom. Finally, we introduce the reader to the key ingredients of two experimental probes of magnetization dynamics, spin transport and NV-center relaxometry setups, and discuss experimental findings relevant to the outlined theory. [ABSTRACT FROM AUTHOR]

Spin-wave based computing requires materials with low Gilbert damping, such as Ni 80 Fe 20 (Permalloy) or yttrium iron garnet, in order to allow for spin-wave propagation on a length scale comparable to the device size. Many devices, especially those that rely on spin–orbit effects for operation, are subject to intense Joule heating, which can exacerbate electromigration and induce local phase changes. Here, the effect of annealing on the Gilbert damping coefficient α of 36 nm Py thin films grown on a Si substrate is examined. Ferromagnetic resonance measurements, high resolution transmission electron microscopy, as well as energy dispersive x-ray spectroscopy have been employed to determine α while also studying structural changes in the thin films. The Gilbert damping parameter was found to increase sixfold when annealed at 350 ° C, which was linked to the diffusion of Ni atoms into the Si substrate on a length scale of up to 50 nm. The results demonstrate that magnonic devices have to be treated with caution when Joule heating occurs due to its detrimental effects on the magnonic properties, but the effect can potentially be exploited in the fabrication of magnonic devices by selectively modifying the magnonic damping locally. [ABSTRACT FROM AUTHOR]

Spin waves, whose quanta are called magnons, are propagating excitations of magnetic materials. Magnonics is an emerging field of modern condensed matter physics that aims to study and utilize the properties and behaviors of magnons. The topological magnon band is an interesting topic of magnonics, and nontrivial topology is usually accompanied with many exotic phenomena such as emergence of robust edge states and the magnon Hall effect. In this Tutorial, using a honeycomb ferromagnet as a prototypical platform, we pedagogically demonstrate how to compute the magnon spectra and the topological invariants characterizing the topology of the magnon bands. We also briefly discuss some numerical techniques. [ABSTRACT FROM AUTHOR]

The topological one-way waveguide mode of the acoustic wave has recently been demonstrated in various meta-structure systems. Here, we show that in a topological phononic crystal with a symmetry-broken acoustic unit cell, the topological state possesses not just a "spin-like" pseudospin mode but also real spin angular momentum. By rotating the double-square units, the band of the phononic crystal will become inverse and induce both topological phase transition and spin angular momentum reversal. As such, by putting two topologically different systems together, the spin angular momentum dependent one-way interface modes can be selectively excited by acoustic spin sources, exhibiting robust transport protected by tight spin-momentum locking. The spin angular momentum density distribution in the unit cell and edge states shows that in addition to the pseudospin, there is a strong correlation between the real spin angular momentum and topological properties in this acoustic system, producing the topologically selective acoustic torque. Revealing the real spin angular momentum and associated acoustic spin torque properties of these topological phononic and acoustic systems will give people a more general understanding about symmetric breaking wave systems and help people to explore more potential applications of acoustic spins in various topological systems. [ABSTRACT FROM AUTHOR]

A spin-wave delay-line active-ring oscillator has recently been proposed as a suitable substrate to implement the physical reservoir computing model. The concept displays the required properties of fading memory and nonlinearity characteristic to the model. In this paper, we improve the concept by increasing the signal delay time in the yttrium-iron garnet film by more than four times, and we examine further the improved system by evaluating experimentally the performance on two benchmark classification tasks. The short-term memory (STM) task evaluates the linear memory characteristics of the RC, while the parity-check (PC) task evaluates the nonlinear computing capability. Adequate performance on both is achieved, and the linear memory is shown to be strongly dependent on the synchronization between the reservoir computer (RC) inputs and the active-ring circulation time. The extended delay time and other major improvements result in STM and PC capacities reaching maximum values of 4.68 and 1.74, respectively. [ABSTRACT FROM AUTHOR]

In magnonics, magnetic waves and oscillations are exploited for signal and information processing at microwave frequencies. A magnonic metamaterial is employed to configure different microwave bands by spatial engineering of magnetizations using different magnetic states or magnetic couplings. Magnetic field hysteretic variation of microwave responses has conventionally been used for tunable microwave operations. The use of such bias magnetic fields hinders the device integration of microwave magnonic devices. Here, we discuss a route to eliminating the requirement of bias magnetic field and simple initialization process for reconfigurable microwave operations. The distinct microwave responses are associated with different remanent magnetic states which are engineered by shape induced magnetic anisotropy rather than the conventional dipolar coupling driven magnetic states. However, the origin of the shift in the microwave spectra is associated with the variation of dipolar coupling for nanomagnetic networks, multilayer nanomagnets, and their arrays. This perspective provides an outlook on current challenges and potential future scopes of magnonic devices. We discuss some of our recent demonstrations toward the realizations of reconfigurable magnonic devices without any external bias magnetic field. Self-biased nanomagnets are also shown to have applications in designing a waveguide for spin wave transport and spin wave gating which operates without any bias magnetic field. [ABSTRACT FROM AUTHOR]

The present work focuses on the effect of vanadium dioxide (VO2) films exhibiting a metal–insulator transition (MIT) on the performance characteristics of the magnetic multilayers. It has been shown that the MIT provides a novel mechanism for controlling the microwave spin-wave dynamics in the yttrium iron garnet (YIG) films. In particular, the low and high levels of microwave attenuation of spin waves transmitted through the YIG–VO2 bilayer has been observed due to a variation of the VO2 conductivity within a narrow temperature range. This effect has been utilized to realize fully reconfigurable magnonic crystals composed of the thickness-modulated YIG and regular VO2 films. A promising functionality of the proposed waveguiding structures arises from a controllability of wave intensity, which provides an altering of the frequency response from an original band structure to a full rejection of spin waves. Numerical simulations taking into account both the YIG film saturation magnetization and the VO2 film conductivity have confirmed the experimentally observed spin-wave dynamics. An interest in ferrite–VO2 bilayers arises not only from possible practical applications but also from a variety of fundamental scientific problems devoted to the physics of wave phenomena in planar thin-film magnetic multilayers. [ABSTRACT FROM AUTHOR]

A three-input majority gate, which operates on the basis of majority decisions, can function as multifunctional Boolean logic gates. Here, we report a micromagnetic simulation study of a specially devised magnonic majority-logic gate that utilizes channeling of spin waves into narrow domain walls. Our model system is a four-armed cross structure where low-energy spin waves are guided and channeled along Néel-type domain walls and then interact with a single magnetic vortex positioned at the cross-point. After exciting spin waves simultaneously from the ends of three individual arms where input binary digits are encoded using spin-wave phase information, the phases of spin waves passing through the cross-point (after being scattered from the vortex) are measured as output binary digits at the end of the remaining single output arm. Consequently, the majority of the input variables determines the output signal, which is a clear sign of a majority gate. Furthermore, by setting a control input, our proposed single structure can perform multiple operations of AND-, OR-, NAND-, and NOR-gates. Finally, the gate structure and channeling spin waves into domain walls/their interaction with a vortex core have the additional merits of being free of the Joule heating typically encountered in conventional electronic devices and of having long coherence lengths. [ABSTRACT FROM AUTHOR]

This paper provides a tutorial overview over recent vigorous efforts to develop computing systems based on spin waves instead of charges and voltages. Spin-wave computing can be considered a subfield of spintronics, which uses magnetic excitations for computation and memory applications. The Tutorial combines backgrounds in spin-wave and device physics as well as circuit engineering to create synergies between the physics and electrical engineering communities to advance the field toward practical spin-wave circuits. After an introduction to magnetic interactions and spin-wave physics, the basic aspects of spin-wave computing and individual spin-wave devices are reviewed. The focus is on spin-wave majority gates as they are the most prominently pursued device concept. Subsequently, we discuss the current status and the challenges to combine spin-wave gates and obtain circuits and ultimately computing systems, considering essential aspects such as gate interconnection, logic level restoration, input–output consistency, and fan-out achievement. We argue that spin-wave circuits need to be embedded in conventional complementary metal–oxide–semiconductor (CMOS) circuits to obtain complete functional hybrid computing systems. The state of the art of benchmarking such hybrid spin-wave–CMOS systems is reviewed, and the current challenges to realize such systems are discussed. The benchmark indicates that hybrid spin-wave–CMOS systems promise ultralow-power operation and may ultimately outperform conventional CMOS circuits in terms of the power-delay-area product. Current challenges to achieve this goal include low-power signal restoration in spin-wave circuits as well as efficient spin-wave transducers. [ABSTRACT FROM AUTHOR]

Magnetic droplet solitons are dynamical magnetic textures that form due to an attractive interaction between spin waves in thin films with perpendicular magnetic anisotropy. Spin currents and the spin torques associated with these currents enable their formation as they provide a means to excite non-equilibrium spin-wave populations and compensate their decay. Recent years have seen rapid advances in experiments that realize and study magnetic droplets. Important advances include the first direct x-ray images of droplets, determination of their threshold and sustaining currents, measurement of their generation and annihilation time, and evidence for drift instabilities, which can limit their lifetime. This perspective discusses these studies and contrasts these solitons to other types of spin-current excitations, such as spin-wave bullets, and static magnetic textures, including magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as current controlled microwave frequency oscillators with potential applications in neuromorphic chips as nonlinear oscillators with memory. [ABSTRACT FROM AUTHOR]

Two-dimensional materials are ideal candidates to host Charge Density Waves (CDWs) that exhibit paramagnetic limiting behavior, similar to the well-known case of superconductors. Here, we study how CDWs in two-dimensional systems can survive beyond the Pauli limit when they are subjected to a strong magnetic field by developing a generalized mean-field theory of CDWs under Zeeman fields that includes incommensurability, imperfect nesting, and temperature effects and the possibility of a competing or coexisting Spin Density Wave (SDW) order. Our numerical calculations yield rich phase diagrams with distinct high-field phases above the Pauli limiting field. For perfectly nested commensurate CDWs, a q -modulated CDW phase that is completely analogous to the superconducting Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase appears at high fields. In the more common case of imperfect nesting, the commensurate CDW ground state undergoes a series of magnetic-field-induced phase transitions first into a phase where commensurate CDW and SDW coexist and subsequently into another phase where CDW and SDW acquire a q -modulation that is, however, distinct from the pure FFLO CDW phase. The commensurate CDW + SDW phase occurs for fields comparable to but less than the Pauli limit and survives above it. Thus, this phase provides a plausible mechanism for the CDW to survive at high fields without the need for forming the more fragile FFLO phase. We suggest that the recently discovered 2D materials like the transition metal dichalcogenides offer a promising platform for observing such exotic field-induced CDW phenomena. [ABSTRACT FROM AUTHOR]

The spin–orbit torque induced by a topological insulator (TI) is theoretically examined for spin wave generation in a neighboring antiferromagnetic thin film. The investigation is based on the micromagnetic simulation of Néel vector dynamics and the analysis of transport properties in the TI. The results clearly illustrate that propagating spin waves can be achieved in the antiferromagnetic thin-film strip through localized excitation, traveling over a long distance. The oscillation amplitude gradually decays due to the non-zero damping as the Néel vector precesses around the magnetic easy axis with a fixed frequency. The frequency is also found to be tunable via the strength of the driving electrical current density. While both the bulk and the surface states of the TI contribute to induce the effective torque, the calculation indicates that the surface current plays a dominant role over the bulk counterpart except in the heavily degenerate cases. Compared to the more commonly applied heavy metals, the use of a TI can substantially reduce the threshold current density to overcome the magnetic anisotropy, making it an efficient choice for spin wave generation. The Néel vector dynamics in the nano-oscillator geometry are examined as well. [ABSTRACT FROM AUTHOR]

Using an atomistic spin model, we have simulated spin wave injection and propagation into antiferromagnetic IrMn from an exchange coupled CoFe layer. The spectral characteristics of the exited spin waves have a complex beating behavior arising from the non-collinear nature of the antiferromagnetic order. We find that the frequency response of the system depends strongly on the strength and frequency of oscillating field excitations. We also find that the strength of excited spin waves strongly decays away from the interfacial layer with a frequency dependent attenuation. Our findings suggest that spin waves generated by coupled ferromagnets are too weak to reverse IrMn in their entirety even with resonant excitation of a coupled ferromagnet. However, efficient spin wave injection into the antiferromagnet is possible due to the non-collinear nature of the IrMn spin ordering. [ABSTRACT FROM AUTHOR]

Field- and fluence-dependent spin-wave dynamics in full-Heusler Co2FeAl0.5Si0.5 films are studied by using time-resolved magneto-optical polar Kerr spectroscopy. Volume magnetostatic spin-wave (VMSW) and perpendicular standing spin-wave (PSSW) modes are excited in the films with thicknesses of 60 and 100 nm, while only the Kittel mode is observed in the films with thicknesses of 150 and 200 nm. The amplitudes of all three spin-wave modes increase with increasing field and fluence, and the frequencies slightly decrease with increasing fluence as expected. The lifetimes and effective damping are found to be modulated by both the external field and excitation fluence. The effective damping of VMSW and Kittel modes presents strong field dependences that are significantly different from each other and can be attributed to the field-dependent group velocity and magnetic inhomogeneity, respectively. In addition, the effective damping of VMSW and PSSW modes increases with increasing fluence, showing a dominant mechanism of electron–phonon scattering enhancement. However, that of the Kittel mode decreases with increasing fluence and further demonstrates the dominant contribution from magnetic inhomogeneity in this case, which is inferred to suppress the excitation of the VMSW mode. [ABSTRACT FROM AUTHOR]

We theoretically study the interaction of magnons, quanta of spin waves, and a domain wall in a one-dimensional easy-axis antiferromagnet in the presence of an external magnetic field applied along the easy axis. To this end, we begin by obtaining the exact solution for spin waves in the background of a domain wall magnetized by an external field. The finite magnetization inside the domain wall is shown to give rise to reflection of magnons scattering off the domain wall, deviating from the well-known result of reflection-free magnons in the absence of a magnetic field. For practical applications of the predicted reflection of magnons, we show that the magnon reflection contributes to the thermally driven domain-wall motion. Our work leads us to envision that inducing a finite magnetization in antiferromagnetic solitons such as vortices and skyrmions can be used to engender phenomena that do not occur in the absence of magnetization. [ABSTRACT FROM AUTHOR]

We studied, by micromagnetic simulations, the characteristic propagation behaviors of specific spin-wave modes along narrow domain walls in a specially designed thin-film-nanostrip cross-structure waveguide as well as their novel interaction behaviors with a single magnetic vortex placed at the cross-point. Only certain specific modes of spin waves well propagate along the given domain walls and then interact with the magnetic vortex. Through this robust interaction, vortex-gyration motions are also stimulated, which exhibit circular- and/or elliptical-shape core trajectories at the same frequencies as those of the pumping spin waves. The elliptical core trajectories of the stimulated vortex gyrations can be interpreted by the superposition of different amplitudes and phases of the clockwise and counterclockwise circular eigenmodes. According to the action–reaction effect, the phase and the amplitude of the propagating spin waves that pass through the vortex structure are modified differently into different arms of the nanostrip cross-structure. Thereby, the propagating spin waves are allowed to be transmitted and scattered with contrasting phases and amplitudes in different branch arms. This work provides a fundamental understanding of the interaction of spin waves propagating along domain walls with a magnetic soliton and also suggests potential applications to magnonic information processing devices. [ABSTRACT FROM AUTHOR]

Spin-wave bandpass filters with small sizes on the basis of thin Y 3 Fe 5 O 12 [yttrium-iron garnet (YIG)] films on Gd 3 Ga 5 O 12 [gadolinium-gallium garnet (GGG)] and SiO 2 / Si substrates have been constructed. A thin YIG film with a thickness of 0.8 μ m on SiO 2 / Si substrates has been grown by the ion-beam sputtering. It is found that the coplanar antenna structure can be successfully used to construct tunable small-sized narrowband bandpass filters based on spin waves. The filter transmission characteristic has a nonreciprocity when the direction of energy propagation changes. Spin-wave filter characteristics are analyzed using the transmission-matrix formalism. [ABSTRACT FROM AUTHOR]

The field of magnonics, which utilizes propagating spin waves for nanoscale transmission and processing of information, has been significantly advanced by the advent of the spin–orbit torque. The latter phenomenon allows one to overcome two main drawbacks of magnonic devices—low energy efficiency of the conversion of electrical signals into spin-wave signals and fast spatial decay of spin waves in thin-film waveguiding structures. At first glance, the excitation and amplification of spin waves by spin–orbit torques seem to be straightforward. Recent research indicates, however, that the lack of the mode selectivity in the interaction of spin currents with dynamic magnetic modes and the onset of dynamic nonlinear phenomena represent significant obstacles. Here, we discuss the possible route to overcoming these limitations, based on the suppression of nonlinear spin-wave interactions in magnetic systems with perpendicular magnetic anisotropy. We show that this approach enables efficient excitation of coherent magnetization dynamics and propagating spin waves in extended spatial regions and is expected to enable practical implementation of complete compensation of spin-wave propagation losses. [ABSTRACT FROM AUTHOR]

We study magnetic, transport, and thermal properties of Co2C and Co3C nanocomposites mixed in a 1:1 ratio. The nanocomposite has clusters with an average diameter of 40 ± 15 nm. We show that the behavior of the nanocomposite is completely different from that of only Co3C or Co2C. We observed that with decreasing temperature, the saturation magnetization MS(T) increases, with a steep rise seen below 100 K. A detailed analysis shows that the increase in MS(T) down to 100 K is explained via a surface spin freezing model. However, below 100 K, the steep increase in MS(T) is explained by a finite size effect related to the confinement of spin waves within nanoparticles. Heat capacity measurements show a broad peak at 100 K along with a low temperature anomaly at 43 K (=Tex). Resistance measurements of the nanocomposite show metallic behavior at high T with an anomalous feature appearing at Tex, which is near the T regime, where MS(T) begins to increase steeply. A measurement of the temperature gradients across the sample thickness indicates an abrupt change in thermal conductivity at Tex. Our results suggest a transformation from a magnetically coupled state with a continuous spectrum of spin waves into a magnetically decoupled state below 100 K with confined spin waves. [ABSTRACT FROM AUTHOR]

The theory of spin-wave resonance in gradient ferromagnetic films with magnetic parameters varying in space described by both concave and convex quadratic functions is developed. Gradient structures such as a potential well, a potential barrier, and a monotonic change in potential between the film surfaces for both quadratic functions are considered. The waveforms of oscillations m n (z) , the laws of the dependence of discrete frequencies ω n , and relative susceptibilities χ n / χ 1 0 of spin-wave resonances on the resonance number n are studied. It is shown that the law ω n ∝ n for n < n c , where n c is the resonance level near the upper edge of the gradient inhomogeneity, which is well known for a parabolic potential well, is also valid for the potential barrier and for the monotonic change in potential, if these structures are formed by a concave quadratic function. It is shown that the law ω n ∝ (n − 1 / 2) 1 / 2 , which we numerically derived and approximated by the analytical formula, is valid for all three structures formed by a convex quadratic function. It is shown that the magnetic susceptibility χ n of spin-wave resonances for n < n c is much greater than the susceptibility of resonances in a uniform film. An experimental study of both laws ω n (n) and χ n (n) would allow one to determine the type of quadratic function that formed the gradient structure and the form of this structure. The possibility of creating gradient films with different laws ω n (n) and the high magnitude of the high-frequency magnetic susceptibility χ n (n) at n < n c make these metamaterials promising for practical applications. [ABSTRACT FROM AUTHOR]

This work is focused on the numerical investigation of spin waves that propagate in nonlinear ferromagnet/superconductor bilayered films and periodic structures. The nonlinearity in these hybrid structures emerges due to the non-monotonous dependence of magnetization of a superconducting subsystem on the magnetic field, which is characterized by the superconducting critical field. It is shown that at relatively high amplitudes of spin waves in comparison to the superconducting critical field, the spin-wave spectrum changes drastically: the spin-wave spectral line can either bifurcate or stretch continuously depending on the type of considered superconductor. In addition, in the case of propagation of spin waves with relatively high amplitude in periodic magnonic metamaterials, additional zero-group-velocity modes appear that are known as flatbands. Overall, these findings suggest a versatile way for tunability of the spin-wave spectrum in nonlinear ferromagnet/superconductor structures by changing the excitation signal in respect to the superconducting critical field. [ABSTRACT FROM AUTHOR]

Abstract Devices for performing computation and logic operations with low‐energy consumption are of key importance for environmentally friendly data processing and information technology. Here, a design for magnetic elements that use excess heat to perform logic operations is presented. The basic information channel is coupled non‐conductive magnetic stripes with a normal metal spacer. The thermal information signal is embodied in magnetic excitations and it can be transported, locally enhanced, and controllably steered by virtue of charge current pulses in the spacer. Functionality of essential thermal logic gates is demonstrated by material‐specific simulations. The operation principle takes advantage of the special material architecture with a balanced gain/loss mechanism for magnetic excitation which renders the circuit parity‐time symmetric with exceptional points tunable by the current strength in the spacer. Heat flow at these points can be enhanced, be non‐reciprocal, or may oscillate between the information channels enabling controlled thermal diode and thermal gate operations. The findings point to a new route for exploiting heat for useful work on the nanoscale.

[Display omitted] Atomically thin van der Waals magnetic materials have not only provided a fertile playground to explore basic physics in the two-dimensional (2D) limit but also created vast opportunities for novel ultrafast functional devices. Here we systematically investigate ultrafast magnetization dynamics and spin wave dynamics in few-layer topological antiferromagnetic MnBi 2 Te 4 crystals as a function of layer number, temperature, and magnetic field. We find laser-induced (de)magnetization processes can be used to accurately track the distinct magnetic states in different magnetic field regimes, including showing clear odd–even layer number effects. In addition, strongly field-dependent AFM magnon modes with tens of gigahertz frequencies are optically generated and directly observed in the time domain. Remarkably, we find that magnetization and magnon dynamics can be observed in not only the time-resolved magneto-optical Kerr effect but also the time resolved reflectivity, indicating strong correlation between the magnetic state and electronic structure. These measurements present the first comprehensive overview of ultrafast spin dynamics in this novel 2D antiferromagnet, paving the way for potential applications in 2D antiferromagnetic spintronics and magnonics as well as further studies of ultrafast control of both magnetization and topological quantum states. [ABSTRACT FROM AUTHOR]

Chirality of antiferromagnetic spin waves as an intrinsic degree of freedom has been attracting considerable attention due to its potential applications for magnonic devices. In this paper, atomistic-scale dynamics simulations were conducted to investigate the chirality of spin wave resonant modes in ferrimagnetic alloy GdxFe1−x (0 < x <1) under different proportion x and external magnetic fields near the angular momentum compensation point. Simulation results reveal that as the proportion of Gd increases, the resonance mode of spin waves undergoes two distinct handedness flipping at magnetization compensation point and angular momentum compensation point. When the proportion x deviates from the magnetization compensation point, a frequency degeneracy point emerges at a non-zero magnetic field, indicating that the chirality of spin waves can also be switched by an external magnetic field. A theoretical analysis is developed to explain the observed phenomena. These findings provide valuable insights into the control and manipulation of spin wave chirality in ferrimagnetic alloys, with potential implications for the development of spin-based devices and technologies. [ABSTRACT FROM AUTHOR]

The high‐frequency optical mode of α‐Fe2O3 is examined, and it is reported that Dzyaloshinskii−Moriya (DM) interaction generates a new type of torque on the magnetic resonance. Using a continuous‐wave terahertz interferometer, the optical mode spectra is measured, where the asymmetric absorption with a large amplitude and broad linewidth is observed near the magnetic transition point, Morin temperature (TM ≈ 254.3 K). Based on the spin wave model, the spectral anomaly is attributed to the DM interaction‐induced torque, enabling to extract the strength of DM interaction field of 4 T. This work opens a new avenue to characterize the spin resonance behaviors at an antiferromagnetic singular point for next‐generation and high‐frequency spin‐based information technologies. [ABSTRACT FROM AUTHOR]

The high‐frequency optical mode of α‐Fe2O3 is examined, and it is reported that Dzyaloshinskii−Moriya (DM) interaction generates a new type of torque on the magnetic resonance. Using a continuous‐wave terahertz interferometer, the optical mode spectra is measured, where the asymmetric absorption with a large amplitude and broad linewidth is observed near the magnetic transition point, Morin temperature (TM ≈ 254.3 K). Based on the spin wave model, the spectral anomaly is attributed to the DM interaction‐induced torque, enabling to extract the strength of DM interaction field of 4 T. This work opens a new avenue to characterize the spin resonance behaviors at an antiferromagnetic singular point for next‐generation and high‐frequency spin‐based information technologies. [ABSTRACT FROM AUTHOR]

Waves exhibit unique characteristics, such as diffraction and interference, which distinguishes them from the particle nature of electrons currently used for binary and sequential data processing and storage. In the solid state, wave properties can be found in electron spin waves in semiconductors or magnons in magnetic materials. These are useful for communication, processing and storage, and allow multiplexing of the information. Given this perspective, after introducing the information theory of wave-parallel computing and arguing the fundamental properties necessary for implementation with wave-based information carriers, we specifically examine how electron spin waves and magnons can be used as information carriers for processing and storage. Then, after explaining the fundamental physics of the electron spin wave based on the persistent spin helix state, we assess the potential of magnon-assisted magnetization switching for realizing the selective writing and reading of multiplexed information. Ferromagnet/semiconductor hybrid structures are emphasized as a platform for generating and controlling both electron spin waves and magnons. Interconversion among light helicity, electron spin waves and magnons is also discussed. Finally, we show several challenges and provide an outlook on the key steps that must be demonstrated for implementing spin-based wave-parallel computing. [ABSTRACT FROM AUTHOR]

Depending on their other constituent elements, Fe-based amorphous materials can exhibit good soft magnetic properties. By determining the directional coefficient b for the relationship of μ0M(μ0H)1/2 according to the best linear fit, it is possible to determine the parameter of spin wave stiffness Dspf. This parameter, amongst others, is related to the distribution of magnetic atoms around the central atom, which is reflected in the value of saturation magnetisation. This work has examined the structure of specially prepared alloy samples and analysed the influence of the spin wave stiffness parameter on the value of saturation magnetisation. Three alloys with different constitutions, based on the Fe matrix, were analysed. [ABSTRACT FROM AUTHOR]

In this paper, we obtain bounds on the Wilson loop expectations in 4D |$U(1)$| lattice gauge theory, which quantify the effect of topological defects. In the case of a Villain interaction, by extending the non-perturbative technique introduced in [ 24 ], we obtain the following estimate for a large loop |$\gamma $| at low temperatures: |$ |\langle W_\gamma \rangle _{\beta }|\leq \exp \Big (-\frac {C_{GFF}} {2\beta }(1+C \beta e^{- 2\pi ^2 \beta })(|\gamma |+o(|\gamma |)) \Big)\,.$| Our result is in line with recent works [ 4 , 9 , 13 , 15 ] which analyze the case where the gauge group is discrete. In the present case where the gauge group is continuous and Abelian, the fluctuations of the gauge field decouple into a Gaussian part, related to the so-called free electromagnetic wave [ 11 , 23 ], and a gas of topological defects. As such, our work gives new quantitative bounds on the fluctuations of the latter which complement the works by Guth and Frölich-Spencer [ 17 , 27 ]. Finally, we improve, also in a non-perturbative way, the correction term from |$e^{-2\pi ^2\beta }$| to |$e^{-\pi ^2\beta }$| in the case of the free-energy of the system. This provides a matching lower-bound with the prediction of Guth [ 27 ] based on renormalization group techniques. [ABSTRACT FROM AUTHOR]

The use of a complex ferromagnetic system to manipulate GHz surface acoustic waves (SAWs) is a rich current topic under investigation, but the high‐power nonlinear regime is under‐explored. Focused SAWs are introduced, which provide a way to access this regime with modest equipment. The symmetry of the magneto‐acoustic interaction can be tuned by interdigitated transducer design which can introduce additional strain components. Here, the impact of focused acoustic waves versus standard unidirectional acoustic waves in significantly enhancing the magnon‐phonon coupling behavior is compared. Analytical simulation results based on the modified Landau–Lifshitz–Gilbert theory show good agreement with experimental findings. Nonlinear input power dependence of the transmission through the device is also reported. This experimental observation is supported by the micromagnetic simulation using mumax3 to model the nonlinear dependence. These results pave the way for extending the understanding and design of acoustic wave devices for the exploration of acoustically driven spin wave resonance physics. [ABSTRACT FROM AUTHOR]

Superconductors are materials with zero electrical resistivity and the ability to expel magnetic fields, which is known as the Meissner effect. Their dissipationless diamagnetic response is central to magnetic levitation and circuits such as quantum interference devices. In this work, we used superconducting diamagnetism to shape the magnetic environment governing the transport of spin waves—collective spin excitations in magnets that are promising on-chip signal carriers—in a thin-film magnet. Using diamond-based magnetic imaging, we observed hybridized spin-wave– Meissner-current transport modes with strongly altered, temperature-tunable wavelengths and then demonstrated local control of spin-wave refraction using a focused laser. Our results demonstrate the versatility of superconductor-manipulated spin-wave transport and have potential applications in spin-wave gratings, filters, crystals, and cavities. [ABSTRACT FROM AUTHOR]

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 μ m 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. [ABSTRACT FROM AUTHOR]

Ferromagnetic insulators with ultra-low damping and tunable magnetic properties are of great interest for the study of spin wave-based phenomena as well as for applications in spin wave spintronics. We have developed epitaxial spinel structure ferrite thin films of Li0.5(AlxFe2.5−x)O4 (LAFO) with ultra-low magnetic damping. The degree of Al substitution tunes the saturation magnetization and in-plane magnetic anisotropy while maintaining excellent epitaxy and crystalline quality as well as low magnetic damping. All LAFO films, deposited on (001)-oriented MgAl2O4 (MAO), are under epitaxial compressive strain, giving rise to an easy magnetic axis in-plane and a hard out-of-plane axis. Element-specific x-ray magnetic circular dichroism measurements confirm that the magnetism originates from the majority of Fe3+ cations occupying the octahedral sites, which are displaced by increased Al3+ substitution. Broadband ferromagnetic resonance reveals the lowest Gilbert damping parameters of 5 × 10 − 4 for films 10–15 nm thick. Our films demonstrate the robustness of the low loss dynamic properties of Li0.5(AlxFe2.5−x)O4 that are promising for spin wave applications. [ABSTRACT FROM AUTHOR]

Spin waves in nanostructures have great potential to be future spintronic information carriers. Here, we report the excitation and modulation of exchange spin waves in Co20Fe60B20 (CoFeB) films by varying magnetic anisotropy. In a 50 nm-thick CoFeB film, the effective excitation of perpendicular standing spin waves (PSSWs) is achieved due to the uniaxial anisotropy induced by oblique sputtering. Additionally, patterning the films into a periodic array of rectangles enables the excitation of both exchange-dominated surface spin waves and PSSWs, with the modulation of spin waves achievable by altering the length–width ratio of the rectangle. It is worth noting that PSSWs are present in the easy axis, whereas surface spin waves are observed in the hard axis, emphasizing the significant influence of shape anisotropy on spin waves. Furthermore, we demonstrate the existence of PSSW in a CoFeB/Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3 (PMN-PT) multiferroic heterostructure. The resonance field of PSSW can be shifted by applying electric fields, which originates from the strain anisotropy driven by the piezoelectric effect. These findings are expected to provide valuable insights for the development of energy-efficient spintronic devices and high-frequency data processing systems. [ABSTRACT FROM AUTHOR]

Many-electron systems undergo a collective Larmor precession in the presence of a magnetic field. In a paramagnetic metal, the resulting spin wave provides insight into the correlation effects generated by the electron-electron interaction. Here, we use dynamical mean-field theory to investigate the collective Larmor precession in the strongly correlated regime, where dynamical correlation effects such as quasiparticle lifetimes and non-quasiparticle states are essential. We study the spin excitation spectrum, which includes a dispersive Larmor mode as well as electron-hole excitations that lead to Stoner damping. We also extract the momentum-resolved damping of slow spin waves. The accurate theoretical description of these phenomena relies on the Ward identity, which guarantees a precise cancellation of self-energy and vertex corrections at long wavelengths. Our findings pave the way towards a better understanding of spin wave damping in correlated materials. The authors provide an application of dynamical mean-field theory to the spin dynamics in strongly correlated electron systems showing the impact of dynamic electron-electron self-energies and vertex functions on the Larmor mode and damping processes. The results show the superior nature of the methodology against simpler random-phase approximation techniques. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the nonreciprocal microwave amplification using a cavity magnonic system, consisting of a passive cavity (i.e., the split-ring resonator), an active feedback circuit integrated with an amplifier, and a ferromagnetic spin ensemble (i.e., a yttrium–iron–garnet sphere). Combining the amplification provided by the active circuit and the nonreciprocity supported by the cavity magnonics, we implement a nonreciprocal amplifier with the functions of both unidirectional amplification and reverse isolation. The microwave signal is amplified by 11.5 dB in the forward propagating direction and attenuated in the reverse direction by −34.7 dB, giving an isolation ratio of 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum technologies, where the device can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the backscattered external noise. Also, it is promising to explore more functions and applications using a cavity magnonic system with a real gain. [ABSTRACT FROM AUTHOR]

Partial wave decomposition is one of the main tools within the modern S-matrix studies. We present a method to compute partial waves for 2 → 2 scattering of spinning particles in arbitrary spacetime dimension. We identify partial waves as matrix elements of the rotation group with definite covariance properties under a subgroup. This allows to use a variety of techniques from harmonic analysis in order to construct a novel algebra of weight-shifting operators. All spinning partial waves are generated by the action of these operators on a set of known scalar seeds. The text is accompanied by a Mathematica notebook to automatically generate partial waves. These results pave the way to a systematic studies of spinning S-matrix bootstrap and positivity bounds. [ABSTRACT FROM AUTHOR]

Dispersion of spin waves in the amorphous ferromagnetic alloy Fe48Ni34P18 can be described within the model of a ferromagnet with random anisotropy: (q) = Aq2 + gμBH + δω(q), where δω(q) is an additional term linear in |q|. The method of small-angle scattering of polarized neutrons is used to prove the importance of the additional term δω(q) in dispersion. The measurements are carried out for different values of the external magnetic field H and neutron wavelength λ. The scattering map of neutrons represents a circle centered at the point q = 0. The stiffness A of spin waves is derived directly from the λ-dependence of the radius of this circle. The spin-wave stiffness A of the amorphous alloy weakly decreases from 140 to 110 meV Å2 as temperature increases from 50 to 300 K. The field dependence of the radius demonstrates the presence of an additional term δω(q) in the form of an energy gap that is almost independent of field and temperature. The value of the additional term is Δ = 0.015 ± 0.002 meV. [ABSTRACT FROM AUTHOR]

It is shown that the energy of a ferromagnetic film deposited onto a paramagnetic or superconducting substrate acquires a contribution in the form of the Dzyaloshinskii–Moriya interaction. This contribution appears as a result of the magnetostatic interaction of the magnetization of the ferromagnetic film with the magnetization induced by it in a paramagnet or by the supercurrent in the superconductor and leads to the removal of the chiral degeneracy, nonreciprocity of spin waves, and the formation of chiral states such as magnetic skyrmions. Our estimates indicate the possibility of experimental observation of predicted effects. [ABSTRACT FROM AUTHOR]

The antiferromagnetic (AFM) spin waves are promising for being utilized in highspeed and energy-efficient information processing. However, the excitation and detection of terahertz spin waves in AFM systems is challenging. Here, we demonstrate low-frequency Raman spectroscopy as a powerful tool for spin-wave detection in AFM systems. We present a systematic study of AFM magnons in Cr2O3, a prototypical uniaxial antiferromagnet, via Raman measurements down to 2.3 cm-1 (69 GHz). We resolved the magnon Zeeman splitting and the spin-flop transition. We further determined the sign of angular momentum of the magnon branches via polarization-resolved Raman processes. We also obtained the anisotropy energy, the g-factor, and the spin-flop field of Cr2O3 as a function of temperatures and magnetic fields. A spin-wave renormalization theory accounts for all experimental observations. [ABSTRACT FROM AUTHOR]

In this experimental study, we explore the potential implementation of logic operations using the interference of propagating spin waves within a device composed of intersecting yttrium iron garnet waveguides with submicrometer width. Our investigation reveals the significant influence of finite-size effects on the performance of the microscopic devices. In particular, we observe that their efficiency depends on the wavelengths of the involved spin waves in relation to the size of the interference region and is reduced by multimode spin-wave propagation. These findings highlight crucial factors to be considered when designing magnonic nanodevices operating with short-wavelength spin waves, providing valuable insights for optimizing their performance in practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Progress in Physics / Wulixue Jinzhan is the property of Progress in Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)