Detection Of Spin Waves Research Articles

Acoustically driven ferromagnetic resonance in YIG thin films

Acoustically driven ferromagnetic resonance (ADFMR) is a platform that enables efficient generation and detection of spin waves via magnetoelastic coupling with surface acoustic waves (SAWs). While previous studies successfully achieved ADFMR in ferromagnetic metals, there are only few reports on ADFMR in magnetic insulators such as yttrium iron garnet (Y3Fe5O12, YIG) despite more favorable spin wave properties, including low damping and long coherence length. The growth of high-quality YIG films for ADFMR devices is a major challenge due to poor lattice-matching and thermal degradation of the piezoelectric substrates during film crystallization. In this work, we demonstrate ADFMR of YIG thin films on LiNbO3 (LNO) substrates. We employed a SiOx buffer layer and rapid thermal annealing for crystallization of YIG films with minimal thermal degradation of LNO substrates. Optimized ADFMR device designs and time-gating measurements were used to enhance the ADFMR signal and overcome the intrinsically low magnetoelastic coupling of YIG. YIG films have a polycrystalline structure with an in-plane easy direction due to biaxial stresses induced during cooling after crystallization. The YIG device shows clear ADFMR patterns with maximum absorption for H ≈ 160 mT parallel to SAW propagation, which is consistent with our simulation results based on existing theoretical models. These results expand possibilities for developing efficient spin wave devices with magnetic insulators.

Spin wave excitation and detection using different meander-shaped antennas: experiment and simulation

The excitation and detection of spin waves (SWs) with specific wavenumbers is very important not only for fundamental SW research but also for the development of future SW devices. Conventional SW theoretical and numerical studies focused on the excitation of dynamic magnetization in waveguides, and did not address the practical limitations imposed by the geometry and configuration of the detection antenna. Using the finite element method, we calculated the induced current with meander-shaped antennas on the detection side, and succeeded in simulating the wavenumber filter effect of SW signals on detection. This was confirmed using experimental measurements on permalloy waveguides. In addition, we investigated, using simulation and experimentally, the effects of combinations of different meander-shaped antennas and broadband signal-ground antennas for excitation and detection. It is found advantageous to set the meander antenna on the detection side to enable filtering and selectivity of SW wavenumber. These findings are important for the development of SW devices.

Single spin magnetometry and relaxometry applied to antiferromagnetic materials

Despite the considerable interest for antiferromagnets that appeared with the perspective of using them for spintronics, their experimental study, including the imaging of antiferromagnetic textures, remains a challenge. To address this issue, quantum sensors, and, in particular, the nitrogen-vacancy (NV) defects in diamond have become a widespread technical solution. We review here the recent applications of single NV centers to study a large variety of antiferromagnetic materials, from quantitative imaging of antiferromagnetic domains and non-collinear states, to the detection of spin waves confined in antiferromagnetic textures and the non-perturbative measurement of spin transport properties. We conclude with recent developments improving further the magnetic sensitivity of scanning NV microscopy, opening the way to detailed investigations of the internal texture of antiferromagnetic objects.

Optical spin-wave detection beyond the diffraction limit

Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, their wave-like nature allows for novel computing paradigms. Conventional methods to detect propagating spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser unless near-field techniques are used. In this article, we demonstrate the magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700nm in 20nm thick Ni80Fe20 strips using a diffraction-limited laser spot with a diameter of 10μm. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing phase-sensitive, wavevector-selective spin-wave detection in the time domain, thus providing a complementary approach to existing techniques such as Brillouin light scattering. This should open up new avenues toward the integration of the burgeoning fields of photonics and magnonics and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research.

Topological states and quantum effects in magnonics

In recent years, with the rapid development of the emerging technologies including the internet of things, cloud computing, big data, and artificial intelligence, higher computing capability is required. Traditional semiconductor devices are confronting huge challenges brought by device miniaturization, energy consumption, heat dissipation, etc. Moore’s law which succeeds in guiding downscaling and upgrading of microelectronics is nearing its end. A new information carrier, instead of electrons, is required urgently for information transmission and processing. Spin waves are collectively excited waves in ordered magnets, and the quantized quasi particle is referred to as magnon. The propagation of magnons does not involve electron motion and produces no Joule heating, which can solve the increasing significant issues of heating dissipation in electronic devices. Thus, magnon-based devices have important application prospects in low-power information storage and computing. In this review, we first introduce the recent advances in the excitation, propagation, manipulation, detection of spin waves and magnon-based devices. Then, we mainly discuss the researches of our group. This part is described from four aspects: 1) Chiral magnonics, including the chiral propagarion of magnetostatic spin waves, Dzyaloshinskii-Moriya interaction(DMI)-induced nonreciprocity of spin waves, spin-wave propagation at chiral interface, magnonic Goos-Hänchen effect, spin-wave lens, and magnonic Stern-Gerlach effect; 2) nonlinear magnonics, including three-magnon processes induced by DMI and noncollinear magnetic textures, skyrmion-induced magnonic frequency comb, twisted magnon frequency comb, and Penrose superradiance; 3) topological magnonics, including magnon Hall effect, magnonic topological insulator, magnonic topological semimetal, topological edge states and high-order corner states of magnetic solitons arranged in different crystal lattices; 4) quantum magnonics, including quantum states of magnon, magnon-based hybrid quantum systems, and cavity magnonics. Finally, the future development and prospect of magnonics are analyzed and discussed.

Spectrally Selective Detection of Short Spin Waves in Magnetoplasmonic Nanostructures via the Magneto-Optical Intensity Effect.

A method of spectrally selective detection of short spin waves (or magnons) by means of the transverse magneto-optical (MO) intensity effect in transmission in the magnetoplasmonic nanostructure is proposed. We considered the spin waves with a wavelength equal to or less than (by an integer number of times) the period of the plasmonic structure, that is, of the order of hundreds of nanometers or 1–2 m. The method is based on the analysis of the MO effect spectrum versus the modulation of the sample magnetization (created by the spin wave) and related spatial symmetry breaking in the magnetic layer. The spatial symmetry breaking leads to the appearance of the MO effect modulation at the normal incidence of light in the spectral range of the optical states (the SPP and the waveguide modes) and the breaking of the antisymmetry of the effect with respect to the sign of the incidence angle of light. We reveal that the magnitude of the MO effect varies periodically depending on the spatial shift of the spin wave with respect to the plasmonic grating. The period of this modulation is equal to the period of the spin wave. All these facts allow for the detection of spin waves of a certain wavelength propagating in a nanostructure by measuring the MO response.

Magnonic Crystal with Strips of Magnetic Nanoparticles: Modeling and Experimental Realization via a Dip-Coating Technique

In this article, we describe a magnonic crystal formed by magnetite nanoparticles. The periodic strip-like structure of the nanoparticles was fabricated on the surface of thin yttrium iron garnet single-crystal film grown on a gallium–gadolinium garnet substrate via dip-coating techniques. It was shown that such periodic structure induces the formation of the bandgaps in the transmission spectra of magnetostatic surface spin-waves (MSSW). The structure was simulated by the transfer matrix method. Spin-wave detection has been carried out by using a pair of microwave antennas and a vector network analyzer.

Imaging Spin‐Wave Damping Underneath Metals Using Electron Spins in Diamond

AbstractSpin waves in magnetic insulators are low‐damping signal carriers that can enable a new generation of spintronic devices. The excitation, control, and detection of spin waves by metal electrodes is crucial for interfacing these devices to electrical circuits. As such, it is important to understand metal‐induced damping of spin‐wave transport, but characterizing this process requires access to the underlying magnetic films. Here it is shown that electronic sensor spins in diamond enable imaging of spin waves that propagate underneath metals in magnetic insulators. This capability is then used to reveal a 100‐fold metal‐induced increase in spin‐wave damping. The damping enhancement is attributed to spin‐wave‐induced electrical currents as well as, above a certain frequency, three‐magnon scattering processes. This interpretation is supported by deriving expressions for the current‐induced damping and the three‐magnon threshold from the Landau–Lifshitz–Gilbert equation that agree well with the observations. The detection of buried scattering centers further highlights the technique's power for assessing spintronic device quality. These results open new avenues for studying metal – spin‐wave interactions and provide access to interfacial processes such as spin‐wave injection via the spin‐Hall effect.

Parametric excitation and mode control using an Oersted field in a NiFe nanowire

Parametric pumping is a nonlinear wave phenomenon and a promising technique for electronic devices based on spin waves, so-called “magnonics”. For parametric excitation, a magnetic nanowire system that has a built-in dc current line to produce an Oersted field is designed, and for spin wave detection, a micro-Brillouin light scattering (μ-BLS) system is used. A spin wave with a frequency of fsw = 5.6 GHz is observed when a pumping microwave with a frequency of fmw = 11.2 GHz is applied. The wave is found to be of the n = 1 width mode (n is the antinode number), and its mode changes to an edge-localized (or possibly n > 1) mode when the Oersted field (or current) varies. Joule heating effects are not observed in the pumping process. Thus, spin wave mode control by the built-in current would be a convenient and useful method to enhance the efficiency and compatibility in applications of spin-based electronics.

Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet

In the Landau levels of a two-dimensional electron system or when flat bands are present, e.g. in twisted van der Waals bilayers, strong electron-electron interaction gives rise to quantum Hall ferromagnetism with spontaneously broken symmetries in the spin and isospin sectors. Quantum Hall ferromagnets support a rich variety of low-energy collective excitations that are instrumental to understand the nature of the magnetic ground states and are also potentially useful as carriers of quantum information. Probing such collective excitations, especially their dispersion {\omega}(k), has been experimentally challenging due to small sample size and measurement constraints. In this work, we demonstrate an all-electrical approach that integrates a Fabry-P\'erot cavity with non-equilibrium transport to achieve the excitation, wave vector selection and detection of spin waves in graphene heterostructures. Our experiments reveal gapless, linearly dispersed spin wave excitations in the E = 0 Landau level of bilayer graphene, thus providing direct experimental evidence for a predicted canted antiferromagnetic order. We show that the gapless spin wave mode propagates with a high group velocity of several tens of km/s and maintains phase coherence over a distance of many micrometers. Its dependence on the magnetic field and temperature agree well with the hydrodynamic theory of spin waves. These results lay the foundation for the quest of spin superfluidity in this high-quality material. The resonant cavity technique we developed offers a powerful and timely method to explore the collective excitation of many spin and isospin-ordered many-body ground states in van der Waals heterostructures and open the possibility of engineering magnonic devices.

High spin mixing conductance and spin interface transparency at the interface of a Co2Fe0.4Mn0.6Si Heusler alloy and Pt

Ferromagnetic materials exhibiting low magnetic damping (α) and moderately high-saturation magnetization are required from the viewpoints of generation, transmission, and detection of spin waves. Since spin-to-charge conversion efficiency is another important parameter, high spin mixing conductance ({g_{r}^{uparrow downarrow}}) is the key for efficient spin-to-charge conversion. Full Heusler alloys, e.g., Co2Fe0.4Mn0.6Si (CFMS), which are predicted to be 100% spin-polarized, exhibit low α. However, g_r^{ uparrow downarrow } at the interface between CFMS and a paramagnet is not fully understood. Here, we report investigations of spin pumping and the inverse spin Hall effect in CFMS/Pt bilayers. Damping analysis indicates the presence of significant spin pumping at the interface of CFMS and Pt, which is also confirmed by the detection of an inverse spin Hall voltage. We show that in CFMS/Pt, g_r^{ uparrow downarrow } (1.70 × 1020 m−2) and the interface transparency (83%) are higher than the values reported for other ferromagnetic/heavy metal systems. We observed a spin Hall angle of ~0.026 for the CFMS/Pt bilayer system.

Spin Wave Excitation, Detection, and Utilization in the Organic-Based Magnet, V(TCNE)x (TCNE = Tetracyanoethylene).

Spin waves, quantized as magnons, have low energy loss and magnetic damping, which are critical for devices based on spin-wave propagation needed for information processing devices. The organic-based magnet [V(TCNE)x ; TCNE = tetracyanoethylene; x ≈ 2] has shown an extremely low magnetic damping comparable to, for example, yttrium iron garnet (YIG). The excitation, detection, and utilization of coherent and non-coherent spin waves on various modes in V(TCNE)x is demonstrated and show that the angular momentum carried by microwave-excited coherent spin waves in a V(TCNE)x film can be transferred into an adjacent Pt layer via spin pumping and detected using the inverse spin Hall effect. The spin pumping efficiency can be tuned by choosing different excited spin wave modes in the V(TCNE)x film. In addition, it is shown that non-coherent spin waves in a V(TCNE)x film, excited thermally via the spin Seebeck effect, can also be used as spin pumping source that generates an electrical signal in Pt with a sign change in accordance with the magnetization switching of the V(TCNE)x . Combining coherent and non-coherent spin wave detection, the spin pumping efficiency can be thermally controlled, and new insight is gained for the spintronic applications of spin wave modes in organic-based magnets.

Spinwave detection by nitrogen-vacancy centers in diamond as a function of probe–sample separation

Magnetic field noise from magnons can reduce the lifetimes of proximate spins and degrade the performance of spin based technologies. However, spatial and temporal averaging over the area of typical field sensors makes measuring magnetic field noise challenging. Here, we use an ensemble of nitrogen-vacancy (NV) point-defects in diamond to measure the spectral profile of thermally excited spinwave noise at room temperature as a function of the distance away from a 20 nm thick Permalloy (Py) thin film. We systematically vary the separation between the NV and Py layers using a silicon-dioxide wedge and measure the longitudinal relaxation rate of the NV center ms = 0 state as a function of the separation. The measured spinwave-induced relaxation of an ensemble of NV centers is well described by a magnetostatic model of dipole fields from the spinwaves. We furthermore find that our all-optical, nonperturbative measurements of the spinwave noise can be used to extract information about the ferromagnetic source, such as magnetization, damping, and fluctuating amplitude. This technique is amenable to application with stand-off from ferromagnetic elements and from buried structures.

Electrical generation and detection of spin waves in polycrystalline YIG/Pt grown on silicon wafers

We studied the magnetic properties of polycrystalline Y3Fe5O12 (YIG) thin films (less than 100 nm) deposited on thermally oxidized silicon wafer by magnetron sputtering and followed by the post-annealing process. Our ferromagnetic resonance (FMR) results demonstrate that sputtering at room temperature combined with the post-annealing treatment can be an efficient method to achieve large-area (inch scale) and highly uniform YIG thin films with a low damping constant α ∼ 7 × 10−3 on cheap oxidized Si wafer. Furthermore, our spin pumping experiments demonstrate that the polycrystalline YIG/Pt system has a good spin mixing conductance, where spin current can be effectively injected into the adjacent Pt layer from YIG through the interface. Then the electrical detection of magnetic properties (e.g., spin waves) of insulating YIG film can be achieved via the inverse spin Hall effect of Pt. The electrical detection of spin waves in the large-area polycrystalline YIG/Pt on silicon wafer may help to develop new spintronic devices (e.g., magnon-based devices) by utilizing the complementary metal-oxide-semiconductor (CMOS) technology.

Thermally controlled confinement of spin wave field in a magnonic YIG waveguide

Methods for detecting spin waves rely on electrodynamical coupling between the spin wave dipolar field and an inductive probe. While this coupling is usually treated as constant, in this work, we experimentally and theoretically show that it is indeed temperature dependent. By measuring the spin wave magnetic field as a function of temperature of, and distance to the sample, we demonstrate that there is both a longitudinal and transversal confinement of the field near the YIG-Air interface. Our results are relevant for spin wave detection, in particular in the field of spin wave caloritronics.

Pulsed spin wave propagation in a magnonic crystal

Amplitude, frequency, and time domain characteristics have been mapped for short spin wave pulses inside a magnonic crystal. A space- and time-resolved magnetoinductive probing system has been used to detail the spin wave spectral, propagation, and evolution characteristics in a geometrically structured yttrium iron garnet film. Experiments have been performed using magnetostatic surface spin waves excited in a chemically-etched magnonic crystal, ultrafast pulsed excitation of the spin waves, and direct spin wave detection using a scannable magnetoinductive probe connected to a synchronized fast oscilloscope. The results show how the frequency discriminating effect of a magnonic bandgap decreases as the excitation pulse width decreases. They also show how the use of rectangular pulses compromise the magnonic crystal performance because of the high frequency components of such pulses. Space and time maps show how these components are transmitted without additional damping.

Phase detection of spin waves in yttrium iron garnet and metal induced nonreciprocity

We report experiments which characterize spin wave propagation in a thin (111) yttrium iron garnet film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film, we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eshbach mode; these arise from avoided crossings associated with the higher, exchange split, standing wave modes along the film normal, the positions of which correlate with the direct absorption measurements of their positions. This information allows a determination of the exchange parameter. Using this technique, we examine the nonreciprocity in spin wave propagation that results from an adjacent metal layer.

Acoustic excitation and electrical detection of spin waves and spin currents in hypersonic bulk waves resonator with YIG/Pt system

We report on the self-consisted semi-analytical theory of magnetoelastic excitation and electrical detection of spin waves and spin currents in hypersonic bulk acoustic waves resonator with ZnO-GGG-YIG/Pt layered structure. Electrical detection of acoustically driven spin waves occurs due to spin pumping from YIG to Pt and inverse spin Hall (ISHE) effect in Pt as well as due to electrical response of ZnO piezotransducer. The frequency-field dependences of the resonator frequencies and ISHE voltage $U_{ISHE}$ are correlated with experimental ones observed previously. Their fitting allows to determine some magnetic and magnetoelastic parameters of YIG. The analysis of the YIG film thickness influence on $U_{ISHE}$ gives the possibility to find the optimal thickness for maximal $U_{ISHE}$ value.

Electroacoustic Excitation of Spin Waves and Their Detection due to the Inverse Spin Hall Effect

Abstract—In this paper, we present theoretical and experimental results on the excitation and detection of spin waves and spin currents in multifrequency bulk acoustic wave resonators containing iron–yttrium garnet (YIG) films in contact with the Pt film. Acoustically excited magnetic precession under the resonator conditions was established to produce spin pumping that also has a resonance character. A significant asymmetry in the frequency dependence of the voltage signal detected on the Pt film is revealed with respect to the frequency of the magnetoelastic resonance and is confirmed by theoretical calculations. Acoustic resonator spectroscopy in combination with the electric detection of magnetic dynamics using the inverse spin Hall effect is shown to be of interest for studying the dispersion of spin waves, as well as magnetic and magnetoelastic parameters of ferromagnetic films.

Electrical generation and detection of spin waves in a quantum Hall ferromagnet.

Spin waves are collective excitations of magnetic systems. An attractive setting for studying long-lived spin-wave physics is the quantum Hall (QH) ferromagnet, which forms spontaneously in clean two-dimensional electron systems at low temperature and in a perpendicular magnetic field. We used out-of-equilibrium occupation of QH edge channels in graphene to excite and detect spin waves in magnetically ordered QH states. Our experiments provide direct evidence for long-distance spin-wave propagation through different ferromagnetic phases in the N = 0 Landau level, as well as across the insulating canted antiferromagnetic phase. Our results will enable experimental investigation of the fundamental magnetic properties of these exotic two-dimensional electron systems.