Showing papers on "Spin wave published in 2014"
TL;DR: Interesting dynamic features including classical Rabi-like oscillation, magnetically induced transparency, and the Purcell effect are demonstrated in this highly versatile platform, highlighting its great potential for coherent information processing.
Abstract: We realize a cavity magnon-microwave photon system in which a magnetic dipole interaction mediates strong coupling between the collective motion of a large number of spins in a ferrimagnet and the microwave field in a three-dimensional cavity. By scaling down the cavity size and increasing the number of spins, an ultrastrong coupling regime is achieved with a cooperativity reaching 12 600. Interesting dynamic features including classical Rabi-like oscillation, magnetically induced transparency, and the Purcell effect are demonstrated in this highly versatile platform, highlighting its great potential for coherent information processing.
738 citations
TL;DR: Large normal-mode splitting between a magnetostatic mode (the Kittel mode) in a ferromagnetic sphere of yttrium iron garnet and a microwave cavity mode is demonstrated.
Abstract: We demonstrate large normal-mode splitting between a magnetostatic mode (the Kittel mode) in a ferromagnetic sphere of yttrium iron garnet and a microwave cavity mode. Strong coupling is achieved in the quantum regime where the average number of thermally or externally excited magnons and photons is less than one. We also confirm that the coupling strength is proportional to the square root of the number of spins. A nonmonotonic temperature dependence of the Kittel-mode linewidth is observed below 1 K and is attributed to the dissipation due to the coupling with a bath of two-level systems.
697 citations
TL;DR: It is demonstrated that the density of magnons flowing from the transistor’s source to its drain can be decreased three orders of magnitude by the injection of Magnon–magnon interactions into the transistor's gate.
Abstract: An attractive direction in next-generation information processing is the development of systems employing particles or quasiparticles other than electrons--ideally with low dissipation--as information carriers. One such candidate is the magnon: the quasiparticle associated with the eigen-excitations of magnetic materials known as spin waves. The realization of single-chip all-magnon information systems demands the development of circuits in which magnon currents can be manipulated by magnons themselves. Using a magnonic crystal--an artificial magnetic material--to enhance nonlinear magnon-magnon interactions, we have succeeded in the realization of magnon-by-magnon control, and the development of a magnon transistor. We present a proof of concept three-terminal device fabricated from an electrically insulating magnetic material. We demonstrate that the density of magnons flowing from the transistor's source to its drain can be decreased three orders of magnitude by the injection of magnons into the transistor's gate.
694 citations
TL;DR: The spin Hall angles largely vary as Z(4) (Z: atomic number), corroborating the role of spin-orbit coupling in spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au.
Abstract: We have investigated spin pumping from ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ thin films into Cu, Ag, Ta, W, Pt, and Au with varying spin-orbit coupling strengths. From measurements of Gilbert damping enhancement and inverse spin Hall signals spanning 3 orders of magnitude, we determine the spin Hall angles and interfacial spin mixing conductances for the six metals. The spin Hall angles largely vary as ${Z}^{4}$ ($Z$: atomic number), corroborating the role of spin-orbit coupling. Amongst the four 5d metals, the variation of the spin Hall angle is dominated by the sensitivity of the $d$-orbital moment to the $d$-electron count, confirming theoretical predictions.
470 citations
TL;DR: The latest developments in the study of a quantum spin liquid are described, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found.
Abstract: The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare-earth pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic state with an emergent gauge freedom. Spin ices provide one of very few experimentally realized examples of fractionalization because their elementary excitations can be regarded as magnetic monopoles and, over some temperature range, spin ice materials are best described as liquids of these emergent charges. In the presence of quantum fluctuations, one can obtain, in principle, a quantum spin liquid descended from the classical spin ice state characterized by emergent photon-like excitations. Whereas in classical spin ices the excitations are akin to electrostatic charges with a mutual Coulomb interaction, in the quantum spin liquid these charges interact through a dynamic and emergent electromagnetic field. In this review, we describe the latest developments in the study of such a quantum spin ice, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found.
358 citations
TL;DR: Four CuAu-I-type metallic antiferromagnets are investigated for their potential as spin current detectors using spin pumping and inverse spin Hall effect, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of thespin Hall effect in their antiferromeagnetic alloys.
Abstract: We investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship $\mathrm{PtMn}g\mathrm{IrMn}g\mathrm{PdMn}g\mathrm{FeMn}$, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spin Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.
351 citations
TL;DR: In this paper, a theoretical model for the longitudinal spin-Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator (FMI) such as yttrium iron garnet (YIG), and a normal metal (NM), such as platinum (Pt), was presented.
Abstract: We present a theoretical model for the longitudinal spin-Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator (FMI), such as yttrium iron garnet (YIG), and a normal metal (NM), such as platinum (Pt), that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the FMI. We show that the spin current pumped into the NM layer by the magnon accumulation in the FMI provides continuity of the spin current at the FMI/NM interface and is essential for the existence of the longitudinal spin-Seebeck effect. The results of the theory are in good agreement with experimental data for the variation of the LSSE with the sample temperature and with the FMI layer thickness in YIG/Pt bilayers.
256 citations
TL;DR: In this paper, the authors present an experimental study of spin-wave excitation and propagation in microstructured waveguides consisting of a 100nm thick yttrium iron garnet/platinum bilayer.
Abstract: We present an experimental study of spin-wave excitation and propagation in microstructured waveguides consisting of a 100 nm thick yttrium iron garnet/platinum (Pt) bilayer. The life time of the spin waves is found to be more than an order of magnitude higher than in comparably sized metallic structures, despite the fact that the Pt capping enhances the Gilbert damping. Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the spin-wave mode structure for different excitation frequencies. An exponential spin-wave amplitude decay length of 31 μm is observed which is a significant step towards low damping, insulator based micro-magnonics.
177 citations
TL;DR: In this paper, a multiferroic element consisting of a magnetostrictive Ni film and a piezoelectric [Pb(Mg1/3Nb2/3)O3](1−x)−[PbTiO3]x substrate was used for the demonstration of voltage-driven spin wave excitation.
Abstract: In this work, we report on the demonstration of voltage-driven spin wave excitation, where spin waves are generated by multiferroic magnetoelectric (ME) cell transducers driven by an alternating voltage, rather than an electric current. A multiferroic element consisting of a magnetostrictive Ni film and a piezoelectric [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x substrate was used for this purpose. By applying an AC voltage to the piezoelectric, an oscillating electric field is created within the piezoelectric material, which results in an alternating strain-induced magnetic anisotropy in the magnetostrictive Ni layer. The resulting anisotropy-driven magnetization oscillations propagate in the form of spin waves along a 5 μm wide Ni/NiFe waveguide. Control experiments confirm the strain-mediated origin of the spin wave excitation. The voltage-driven spin wave excitation, demonstrated in this work, can potentially be used for low-dissipation spin wave-based logic and memory elements.
172 citations
TL;DR: In this paper, the thermal Hall conductivity of magnons described by a noninteracting boson Hamiltonian is derived by the linear response theory, which covers various spin waves, such as spin waves in antiferromagnets and magnetostatic spin waves.
Abstract: Thermal Hall conductivity of magnons described by a noninteracting boson Hamiltonian is derived by the linear response theory. The thermal Hall conductivity is expressed by the Berry curvature in momentum space, which also has the prevailing form for bosonic systems. This theory covers various spin waves, such as spin waves in antiferromagnets and magnetostatic spin waves. As an example, we calculate the thermal Hall conductivity by the magnetostatic spin wave in yttrium iron garnet and reveal its dependence on a magnetic field and temperature.
168 citations
TL;DR: In this paper, the dynamics of individual magnetic skyrmions confined in ultrathin film dots is studied theoretically, and particular attention is given to the dynamic response of the skyrms to perpendicular magnetic anisotropy.
Abstract: The dynamics of individual magnetic skyrmions confined in ultrathin film dots is studied theoretically. The systems considered are transition-metal ferromagnets possessing perpendicular magnetic anisotropy and particular attention is given to the dynamic response of the skyrmions to perpendicular ac fields. By using micromagnetics simulations, it is shown that breathing modes can hybridize with geometrically quantized spin wave eigenmodes of the circular dots, leading to distinct features in the power spectrum that differ from the behavior expected for uniformly magnetized systems. The static field dependence of the breathing mode frequency offers a direct means of detecting and characterizing such skyrmion states in experiment.
TL;DR: In this paper, the authors studied the dynamics of magnons in the presence of a single skyrmion in chiral magnets featuring Dzyaloshinskii-Moriya interaction.
Abstract: We study theoretically the dynamics of magnons in the presence of a single skyrmion in chiral magnets featuring Dzyaloshinskii-Moriya interaction. We show by micromagnetic simulations that the scattering process of magnons by a skyrmion can be clearly defined although both originate in the common spins. We find that (i) the magnons are deflected by a skyrmion, with the angle strongly dependent on the magnon wave number due to the effective magnetic field of the topological texture, and (ii) the skyrmion motion is driven by magnon scattering through exchange of the momenta between the magnons and a skyrmion: the total momentum is conserved. This demonstrates that the skyrmion has a well-defined, though highly non-Newtonian, momentum.
TL;DR: In this article, it was shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current Idc flowing through the adjacent normal metal with strong spin-orbit interaction.
Abstract: It is demonstrated that the threshold current for damping compensation can be reached in a 5 μm diameter YIG(20 nm)|Pt(7 nm) disk. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of Idc using a magnetic resonance force microscope (MRFM). It is shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current Idc flowing through the adjacent normal metal with strong spin-orbit interaction. Complete compensation of the damping of the fundamental mode by spin-orbit torque is reached for a current density of ∼3×1011 A⋅m−2, in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime
TL;DR: The drift velocity of a moving domain wall is calculated as a result of spin wave-mediated forces and it is shown that the domain wall moves in opposite directions for linearly and circularly polarized waves.
Abstract: Spin waves in antiferromagnets are linearly or circularly polarized. Depending on the polarization, traversing spin waves alter the staggered field in a qualitatively different way. We calculate the drift velocity of a moving domain wall as a result of spin wave-mediated forces and show that the domain wall moves in opposite directions for linearly and circularly polarized waves. The analytical results agree with micromagnetic simulations of an antiferromagnetic domain wall driven by a localized, alternating magnetic field.
TL;DR: The results provide a practical route for the implementation of integrated magnonic circuits utilizing spin transfer, utilizing dipolar field-induced magnonic nanowaveguides that exhibit good spectral matching with spin-torque nano-oscillators and enable efficient directional transmission of spin waves.
Abstract: Magnonic nano-waveguides created by dipolar fields enable efficient coupling and transmission of spin waves generated by spin-torque nano-oscillators.
Journal Article•
TL;DR: Direct imaging of standing spin waves in individual chains of ferromagnetically coupled S = 2 Fe atoms, assembled one by one on a Cu(2)N surface using a scanning tunnelling microscope, opens the way towards atomic-scale imaging of other types of spin excitation, such as spinon pairs and fractional end-states, in engineered spin chains.
Abstract: The excitations that determine the low-temperature properties of ferromagnetic materials are called spin waves. Using a combination of inelastic electron tunnelling spectroscopy and numerical simulations, the spin waves occurring in a one-dimensional chain of iron atoms deposited on Cu2N are now imaged, and their dynamics examined.
TL;DR: An analytical solution to the complex problem of spin waves interacting with a domain wall elucidates how domain walls in an antiferromagnet can be propelled by reflected magnons and, less obviously, by magnons that are passing through them.
Abstract: An analytical solution to the complex problem of spin waves interacting with a domain wall elucidates how domain walls in an antiferromagnet can be propelled by reflected magnons and, less obviously, by magnons that are passing through them.
TL;DR: In this article, the spin current is injected into the ferromagnetic insulator from one side by a metallic reservoir with a nonequilibrium spin accumulation and ejected into another metallic reservoir located downstream.
Abstract: Superfluid spin transport---dissipationless transport of spin---is theoretically studied in a ferromagnetic insulator with easy-plane anisotropy. We consider an open geometry where the spin current is injected into the ferromagnet from one side by a metallic reservoir with a nonequilibrium spin accumulation and ejected into another metallic reservoir located downstream. Spin transport is studied using a combination of magnetoelectric circuit theory, Landau-Lifshitz-Gilbert phenomenology, and microscopic linear-response theory. We discuss how spin superfluidity can be probed in a magnetically mediated negative electron-drag experiment.
TL;DR: In this article, the authors compute the internal modes of a skyrmion in the ferromagnetic background state by numerical diagonalization of the dynamical matrix and find several internal modes below the magnon continuum, such as the mode corresponding to the translational motion and different kinds of breathing modes.
Abstract: A spin texture called skyrmion has been recently observed in certain chiral magnets without inversion symmetry. The observed skyrmions are extended objects with typical linear sizes of 10 nm to 100 nm that contain $10^3$ to $10^5$ spins and can be deformed in response to external perturbations. Weak deformations are characterized by the internal modes which are localized around the skyrmion center. Knowledge of internal modes is crucial to assess the stability and rigidity of these topological textures. Here we compute the internal modes of a skyrmion in the ferromagnetic background state by numerical diagonalization of the dynamical matrix. We find several internal modes below the magnon continuum, such as the mode corresponding to the translational motion, and different kinds of breathing modes. The number of internal modes is larger for lower magnetic fields. Indeed, several modes become gapless in the low field region indicating that the single skyrmion solution becomes unstable, although a skyrmion lattice is thermodynamically stable. On the other hand, at high fields only three internal modes exist and the skyrmion is stable even at higher fields when the ferromagnetic state is thermodynamically stable. We also show that the presence of out-of-plane easy-axis anisotropy stabilizes the single skyrmion solution. Finally, we discuss the effects of damping and possible experimental observations of these internal modes.
TL;DR: In this paper, a linear response formulation of the dc spin pumping was developed in view of describing many-body effects caused by spin fluctuations in the spin sink, and it was shown that when an itinerant ferromagnet near a spin sink was used as the spin sinks, the spin pumping is largely increased owing to the fluctuation enhancement of the spin conductance across the precessing ferromagneticnet/spin sink interface.
Abstract: A linear-response formulation of the dc spin pumping, i.e., a spin injection from a precessing ferromagnet into an adjacent spin sink, is developed in view of describing many-body effects caused by spin fluctuations in the spin sink. It is shown that when an itinerant ferromagnet near ${T}_{\mathrm{C}}$ is used as the spin sink, the spin pumping is largely increased owing to the fluctuation enhancement of the spin conductance across the precessing ferromagnet/spin sink interface. As an example, the enhanced spin pumping from yttrium iron garnet into nickel palladium alloy (${T}_{C}\ensuremath{\simeq}20$ K) is analyzed by means of a self-consistent renormalization scheme, and it is predicted that the enhancement can be as large as tenfold.
TL;DR: In this paper, the Dzyaloshinskii-Moriya (DM) form was used to detect induced DM interactions in metallic multilayers and control spin-wave propagation in ultrathin nanostructures.
Abstract: Ultrathin metallic ferromagnets on substrates with strong spin-orbit coupling can exhibit induced chiral interactions of the Dzyaloshinskii-Moriya (DM) form. For systems with perpendicular anisotropy, the presence of DM interactions has important consequences for current-driven domain-wall motion and underpins possible spintronic applications involving skyrmions. We show theoretically how spin textures driven by the DM interaction allow nonreciprocal channeling of spin waves, leading to measurable features in magnetic wires, dots, and domain walls. Our results provide methods for detecting induced DM interactions in metallic multilayers and controlling spin-wave propagation in ultrathin nanostructures.
TL;DR: These results demonstrate that ferromagnet–normal metal junctions are efficient sources of pure spin currents in the gigahertz frequency range and show that the large a.c. component of the spin currents can be detected efficiently using the inverse spin Hall effect.
Abstract: In spin electronics, the spin degree of freedom is used to transmit and store information. To this end the ability to create pure spin currents—that is, without net charge transfer—is essential. When the magnetization vector in a ferromagnet–normal metal junction is excited, the spin pumping effect leads to the injection of pure spin currents into the normal metal. The polarization of this spin current is time-dependent and contains a very small d.c. component. Here we show that the large a.c. component of the spin currents can be detected efficiently using the inverse spin Hall effect. The observed a.c.-inverse spin Hall voltages are one order of magnitude larger than the conventional d.c.-inverse spin Hall voltages measured on the same device. Our results demonstrate that ferromagnet–normal metal junctions are efficient sources of pure spin currents in the gigahertz frequency range.
TL;DR: A quantum spin liquid is a spin state with no magnetic order even at the lowest temperatures as mentioned in this paper, and it can explain neutron scattering data on a 'kagome lattice' antiferromagnet, in addition to the usual fractionalized spinons.
Abstract: A quantum spin liquid is a spin state with no magnetic order even at the lowest temperatures. To explain neutron scattering data on a ‘kagome lattice’ antiferromagnet, visons (elementary excitations of vortices) must be included, in addition to the usual fractionalized spinons.
TL;DR: In this paper, the effects of spin-lattice coupling on the magnon spectrum of thin ferromagnetic films consisting of the magnetic insulator yttrium iron garnet were investigated.
Abstract: We calculate the effects of the spin-lattice coupling on the magnon spectrum of thin ferromagnetic films consisting of the magnetic insulator yttrium iron garnet. The magnon-phonon hybridization generates a characteristic minimum in the spin dynamic structure factor which quantitatively agrees with recent Brillouin light scattering experiments. We also show that at room temperature the phonon contribution to the magnon damping exhibits a rather complicated momentum dependence: In the exchange regime the magnon damping is dominated by Cherenkov type scattering processes, while in the long-wavelength dipolar regime these processes are subdominant and the magnon damping is two orders of magnitude smaller. We supplement our calculations by actual measurements of the magnon relaxation in the dipolar regime. Our theory provides a simple explanation of a recent experiment probing the different temperatures of the magnon and phonon gases in yttrium iron garnet.
TL;DR: In this article, an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments.
Abstract: We report an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity, and small induced damping, this AuW alloy may find applications in the nearest future.
TL;DR: In this paper, the authors proposed an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation to determine the spin wave spectrum of the magnetic C-site langasites with incomensurate order.
Abstract: Linear spin wave theory provides the leading term in the calculation of the excitation spectra of long-range ordered magnetic systems as a function of $1/\sqrt{S}$. This term is acquired using the Holstein-Primakoff approximation of the spin operator and valid for small $\delta S$ fluctuations of the ordered moment. We propose an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation for the incommensurability. Finally we show, how our model can determine the spin wave spectrum of the magnetic C-site langasites with incommensurate order.
TL;DR: It is demonstrated that one-way transparency can be realized for spin-wave excitations with sufficiently strong optical magnetoelectric effect, and the transparent and absorbing directions of light propagation can be reversed by external magnetic fields.
Abstract: The coupling between spins and electric dipoles governs magnetoelectric phenomena in multiferroics. The dynamical magnetoelectric effect, which is an inherent attribute of the spin excitations in multiferroics, drastically changes the optical properties of these compounds compared with conventional materials where light-matter interaction is expressed only by the dielectric permittivity or magnetic permeability. Here we show via polarized terahertz spectroscopy studies on multiferroic Ca2CoSi2O7, Sr2CoSi2O7 and Ba2CoGe2O7 that such magnetoeletric spin excitations exhibit quadrochroism, that is, they have different colours for all the four combinations of the two propagation directions (forward or backward) and the two orthogonal polarizations of a light beam. We demonstrate that one-way transparency can be realized for spin-wave excitations with sufficiently strong optical magnetoelectric effect. Furthermore, the transparent and absorbing directions of light propagation can be reversed by external magnetic fields. This magnetically controlled optical-diode function of magnetoelectric multiferroics may open a new horizon in photonics.
TL;DR: It is experimentally demonstrated that the spin-orbit interaction can be utilized for direct electric-field tuning of the propagation of spin waves in a single-crystal yttrium iron garnet magnonic waveguide, pointing to an important avenue for manipulating spin waves and developing electrically tunable magnonic devices.
Abstract: In a magnetic material with strong spin-orbit coupling, the phase of spin waves can be controlled with an electric field.
TL;DR: The spin dynamics of all ferromagnetic materials are governed by two types of collective excitations: spin waves and domain walls as mentioned in this paper, and the fundamental processes underlying these collective modes, such as exchange interactions and magnetic anisotropy, all originate at the atomic scale; yet, conventional probing techniques, based on neutron and photon scattering, provide high resolution in reciprocal space, and thereby poor spatial resolution.
Abstract: The spin dynamics of all ferromagnetic materials are governed by two types of collective excitations: spin waves and domain walls. The fundamental processes underlying these collective modes, such as exchange interactions and magnetic anisotropy, all originate at the atomic scale; yet, conventional probing techniques, based on neutron and photon scattering, provide high resolution in reciprocal space, and thereby poor spatial resolution. Here we present direct imaging of spin waves in individual chains of ferromagnetically coupled $S=2$ Fe atoms, assembled one by one on a Cu$_2$N surface using a scanning tunnelling microscope. We are able to map the spin dynamics of these designer nanomagnets with atomic resolution, in two complementary ways. First, atom to atom variations of the amplitude of the quantized spin wave excitations, predicted by theory, are probed using inelastic electron tunnelling spectroscopy. Second, we observe slow stochastic switching between two opposite magnetisation states, whose rate varies strongly depending on the location of the tip along the chain. Our observations, combined with model calculations, reveal that switches of the chain are initiated by a spin wave excited state which has its antinodes at the edges of the chain, followed by a domain wall shifting through the chain from one end to the other. This approach opens the way towards atomic scale imaging of other types of spin excitations, such as spinons and fractional end-states, in engineered spin chains.