Spin Wave Resonance Research Articles

Phase boundary exchange coupling in the mixed magnetic phase regime of a Pd-doped FeRh epilayer

Spin-wave resonance measurements were performed in the mixed magnetic phase regime of a Pd-doped FeRh epilayer that appears as the first-order ferromagnetic-antiferromagnetic phase transition takes place. It is seen that the measured value of the exchange stiffness is suppressed throughout the measurement range when compared to the expected value of the fully ferromagnetic regime, extracted via the independent means of a measurement of the Curie point, for only slight changes in the ferromagnetic volume fraction. This behavior is attributed to the influence of the antiferromagnetic phase: inspired by previous experiments that show ferromagnetism to be most persistent at the surfaces and interfaces of FeRh thin films, we modelled the antiferromagnetic phase as forming a thin layer in the middle of the epilayer through which the two ferromagnetic layers are coupled up to a certain critical thickness. The development of this exchange stiffness is then consistent with that expected from the development of an exchange coupling across the magnetic phase boundary, as a consequence of a thickness dependent phase transition taking place in the antiferromagnetic regions and is supported by complimentary computer simulations of atomistic spin-dynamics. The development of the Gilbert damping parameter extracted from the ferromagnetic resonance investigations is consistent with this picture.

Enhancement of Brillouin light scattering signal with anti-reflection layers on magnetic thin films

The significant enhancement of Brillouin light scattering (BLS) spectroscopy intensity in a ferromagnetic thin film with an additional dielectric anti-reflection layer is experimentally investigated. The anti-reflection layer thickness dependent BLS measurements on ferromagnetic layers are performed systematically. Consequently, we observe that BLS signals are dramatically enhanced by more than 450% at a specific dielectric layer thickness due to the pure optical effect. Because of the large signal enhancements, the errors of the spin wave resonance peak frequencies are noticeably reduced as well. Since many magnetic properties such as the saturation magnetization, the surface anisotropy, and the exchange stiffness constant are determined by the spin wave resonance frequencies from the BLS spectra, the additional anti-reflection layer can help to improve the reliability of BLS experiments. Especially, the BLS signal improvement plays a crucial role in the precise determination of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) energy density, since the iDMI energy density is calculated from the difference of Stokes and anti-Stokes resonance frequencies, which is typically order of 1 GHz.

Brillouin-Mandelstam spectroscopy of stress-modulated spatially confined spin waves in Ni thin films on piezoelectric substrates

We report the results of micro-Brillouin-Mandelstam light scattering spectroscopy of thermal magnons in the two-phase synthetic multiferroic structure consisting of a piezoelectric [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x (PMN-PT) substrate and a Ni thin film. The experimental data reveal the first two modes of the perpendicular standing spin waves (PSSW) spatially confined across the Ni thin film. A theoretical analysis of the frequency dependence of the PSSW peaks on the external magnetic field reveals the asymmetric boundary condition, i.e. pinning, for variable magnetization at different surfaces of the Ni thin film. The strain field induced by applying DC voltage to PMN-PT substrate leads to a downshift of PSSW mode frequency owing to the magneto-elastic effect in Ni, and corresponding changes in the spin-wave resonance conditions. The observed non-monotonic dependence of the PSSW frequency on DC voltage is related to an abrupt change of the pinning parameter at certain values of the voltage. The obtained results are important for understanding the thermal magnon spectrum in ferromagnetic films and the development of the low-power spin-wave devices and quantum sensors.

Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite

Coupling of spin-waves with electromagnetic cavity field is demonstrated in an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at 0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures were found at crossings of spin-wave resonances with Fabry-Perot cavity modes formed in samples. The obtained spectra are explained in terms of classical electrodynamics and a microscopic model.

Ferromagnetic resonance frequency and spin wave mode of asymmetric strip nanomagnet

Recently, the operating frequency of nanomagnetic logic device has reached the spin wave frequency of nanomagnets. Therefore, the dynamic magnetic properties of nanomagnets, which are excited by microwave magnetic field, have been explored by many researchers. In this paper, the micro-magnetic model of asymmetric strip nanomagnets under microwave excitation is established. By using the anisotropic stress field (along the <i>x</i>-axis direction) that is generated by a constant voltage and the SINC function microwave magnetic field (along the <i>y</i>-axis direction) to excite the nanomagnets at the same time, the effects of tilt angle and defect angle on the ferromagnetic resonance (FMR) spectrum and spin wave mode of the asymmetric strip nanomagnets are studied. Spectral analysis is performed on the micromagnetic simulation data. Simulation results show that as the tilt angle of the asymmetric strip nanomagnet increases, the ferromagnetic resonance frequency increases. What is more, this phenomenon is independent of the defect angle of the nanomagnet. When the tilt angle is constant, there exists a monotonically increasing relation between the ferromagnetic resonance frequency of the asymmetric strip nanomagnet and the defect angle. The spin wave modes of the nanomagnets differ a lot as defect angle changes. The asymmetric strip nanomagnet is compared with the rectangle nanomagnet, and the spin wave mode of the asymmetric strip nanomagnet is localized. Specifically, the spin wave mode of the asymmetric strip nanomagnets is asymmetric and the high precession region exists at the edge, which is termed asymmetric edge mode. The changes of the tilt angle lead to the changes in the demagnetizing field inside the nanomagnet, which gives rise to the movement of the edge mode. However, the center mode is not sensitive to the change of tilt angle. Finally, the magnetic loss of the model under the excitation of high frequency microwave magnetic field is analyzed and the reliability of the model is verified. These findings indicate that the defect angle and tilt angle can be used to tune the spin wave mode and the ferromagnetic resonance frequency of nanomagnets, and thus providing an important theoretical basis for designing the tunable microwave nanomagnetic devices.

Спин-волновой резонанс в синтетическом антиферромагнетике [(Co-=SUB=-0.88-=/SUB=-Fe-=SUB=-0.12-=/SUB=-)/Cu]-=SUB=-N-=/SUB=-

The synthetic antiferromagnet [(Co0.88Fe0.12)/Cu]N which is planar composite with ~ 60 nm thickness was researched by the spin-wave resonance technique in all angles range of the applied constant magnetic field relative to normal to the film surface. Our researches demonstrate that studied multilayer film is magnetic superlattice the microwave spectrums of which demonstrate two different exchange-coupled magnetic systems. Every of these subsystems are showing itself as a series spin-wave modes on measured microwave spectrums. The dependence of magnitude of the propagation linear range of standing spin exchange wave on specimen orientation in applied magnetic field was discovered

Ferromagnetic and Spin-Wave Resonance in the [CoFe/Cu]N Superlattice Thin (30-nm) Film

Angular dependences of the microwave absorption spectra of a (CoFe/Cu)N multilayer film have been studied by the ferromagnetic and spin-wave resonance techniques. The critical angle θc indicating the ranges of excitation of uniform and nonuniform spin modes, type of the boundary conditions, and surface anisotropy and exchange coupling constants have been established. It is shown that the accuracy of identification of individual modes in the spectra plays a key role in the analysis of the detected curves.

Ферромагнитный и спин-волновой резонанс в тонкой пленке (30 nm) сверхрешетки [CoFe/Cu]-=SUB=-N-=/SUB=-

Angular dependencies of the spectrum microwave absorption for the multilayer (CoFe/Cu)N film were studied by ferromagnetic and spin-wave resonance method. The critical angle which indicate the boundaries of ranges where the uniform and non-uniform spin modes are excited, the type of boundary conditions, the values of surface anisotropy constant and exchange interaction were defined in this work. It was shown that the precision of identification of every mode in SWR spectrum is key factor to analyze the measured curves

Effect of Structural Inhomogeneities on the Spin-Wave and Magnetic Properties of Monocrystalline Spinel Ferrite Films in the Microwave Range

We have studied magnetic parameters of monocrystalline manganese spinel ferrite films differing in composition and structural perfection and assessed the effect of dislocation distribution on the frequency dependence of the ferromagnetic resonance (FMR) linewidth in the microwave range. The results demonstrate that, if an external magnetic field is perpendicular to the film surface, electron paramagnetic resonance (EPR) absorption lines correspond to ferromagnetic and spin wave resonances (SWRs). SWR is due to nanostructural surface inhomogeneities. The EPR spectrum of a tangently magnetized film represents a single dipole exchange oscillation spectrum. Parameters of dipole and exchange modes have been determined.

Uncovering magnetic properties of NiFe/WTi multilayers by FMR and SWR analyses

Ferromagnetic resonance (FMR) was applied to uncover the magnetic properties of NiFe/WTi multilayers, which showed themselves up as ideal candidates to exemplify the several resonance modes [optic, uniform, and interface FMR modes, volume and surface spin wave resonance (SWR) modes] that can emerge from the probing materials during the measurements: an instructive work to describe what can be revealed by this powerful technique. The absorption modes excited by the microwave field were correlated to important magnetic parameters and characteristic of each multilayer studied by using the FMR and SWR theories and the associated fittings. In particular, the dependence of the damping constant on the thicknesses of magnetic and spacer layers, attributed to both the effects of spin-pumping and mixing of electrical conductance at the magnetic/non-magnetic interfaces, opens the possibility of tailoring the NiFe/WTi structures for specific device applications.

Ionic Liquid Gating Control of Spin Wave Resonance in La0.7Sr0.3MnO3 Thin Film

AbstractMagnonics or spin waves have the potential to serve as the carrier for future information communication. A controllable spin wave resonance (SWR) device is demonstrated in a Au/[DEME]+[TFSI]−/LSMO/STO capacitor heterostructure, which could be regulated by ionic liquid gating (ILG) method. The SWR critical angle φC, excitation position to perform uniform precession, is shifted in a reversible manner (thus recording “off” and “on”) with +1.5 V gating voltage (Vg), measured by quantitative angular dependent electron spin resonance (ESR) spectroscopy. Based on the modified Puszkarski's surface inhomogeneity model, the ILG control SWR at low Vg (Vg < 1.5 V) can be explained by a charge‐doping‐induced effective surface magnetic anisotropy change. Applying a higher Vg (Vg > 1.5 V) enhances the surface mode SWR and gradually diminishes the body mode SWR. Oxygen vacancies generate at higher Vg (Vg > 1.5 V) resulting in the modulation of superexchange between the Mn ions, evidenced by X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy characterization. This ILG control SWR presents a solution for energy efficient and low‐voltage control of magnonics and spin wave devices.

The effect of material defects on resonant spin wave modes in a nanomagnet

We have theoretically studied how resonant spin wave modes in an elliptical nanomagnet are affected by fabrication defects, such as small local thickness variations. Our results indicate that defects of this nature, which can easily result from the fabrication process, or are sometimes deliberately introduced during the fabrication process, will significantly alter the frequencies, magnetic field dependence of the frequencies, and the power and phase profiles of the resonant spin wave modes. They can also spawn new resonant modes and quench existing ones. All this has important ramifications for multi-device circuits based on spin waves, such as phase locked oscillators for neuromorphic computing, where the device-to-device variability caused by defects can be inhibitory.

Spin-Wave Resonance in (Fe0.82Ni0.18)/V Nanostructure

We have studied the transmission of millimeter-range electromagnetic waves through (Fe0.82Ni0.18)/V nanostructure. The dependences of the transmission coefficient in the external magnetic field have been measured. The curves have a minimum caused by energy absorption under the ferromagnetic resonance conditions at frequencies 26–35.6 and 37–38 GHz. In a narrow frequency interval near 36 GHz, a complex pattern of resonance phenomena associated with ferromagnetic and spin-wave resonances is observed. We have calculated the field dependence of the transmission coefficient. It has been established that the model of a homogeneous magnetic metal plate used in calculations makes it possible to reproduce some features of resonant changes in the transmission coefficient, which are induced by ferromagnetic and spin-wave resonances.

Yttrium Iron Garnet Thickness Influence on the Spin Pumping in the Bulk Acoustic Wave Resonator

The features of phonon–magnon interconversion in acoustic resonator determine the efficiency of spin pumping from YIG into Pt that may be detected electrically through the inverse spin Hall effect (ISHE). Based on the methods developed in previous works for calculating resonator structures with a piezoelectric (ZnO) and a magnetoelastic layer in contact with the heavy metal (YIG/Pt), we present the results of numerical calculations of YIG film thickness influence on acoustically driven spin waves. We obtain some YIG film thickness regions with various behavior of dc ISHE voltage UISHE. At micron and submicron thicknesses, the higher spin wave resonance (SWR) modes (both even and odd) can be generated with efficiency comparable and even exceeding that of the main mode. The absolute maximum of UISHE is achieved at the thickness about s1 ≈ 208 nm under the excitation of the first SWR.

Calculation of SWR spectra in two- and three-layer magnetic films

In the present work, the calculation and experimental studies of the spin-wave resonance (SWR) spectra in two- and three-layer magnetic films with dissipative or mixed spin pinning mechanisms are carried out. The calculation showed that the SWR spectra for two-layer ferrite-garnet films have approximately twice the number of spin-wave (SW) modes compared to three-layer films on the same field interval, which is confirmed by experiment. An increase in the mismatch of the dispersion dependences is shown for perpendicular and parallel orientations for a three-layer film compared to a two-layer film. The SW-mode linewidth 2ΔHn in three-layer films is approximately twice as wide in two-layer films for identical values of the wave number.

Simulation of the Interaction of a Magnetic Resonance Force Microscope Probe with a Ferromagnetic Sample

We propose an algorithm and present results of micromagnetic simulation of the resonant response of a probe pickup (cantilever) of a magnetic resonance force microscope. Simulation of induced oscillations of sample magnetization makes it possible to calculate the varying component of the force exerted on the probe by the sample and to construct spectra in the form of dependences of the amplitude of oscillations of the cantilever on the external magnetic field strength. Simulation of time dependences of all magnetization field components makes it possible to analyze the spatial distributions of spin-wave resonances of samples. For test objects in the form of rectangular permalloy microstrips, good agreement between model and experimental spectra is achieved.

Erratum to: Dependence of the Spin-Wave Resonance Spectra in Ferrite–Garnet Films on the Microwave Field Frequency and Damping Parameter

Erratum to: Dependence of the Spin-Wave Resonance Spectra in Ferrite–Garnet Films on the Microwave Field Frequency and Damping Parameter

Damping of Standing Spin Waves in Bismuth-Substituted Yttrium Iron Garnet as Seen via the Time-Resolved Magneto-Optical Kerr Effect

We investigate spin-wave resonance modes and their damping in insulating thin films of bismuth-substituted yttrium iron garnet by performing femtosecond magneto-optical pump-probe experiments. For large magnetic fields in the range below the magnetization saturation, we find that the damping of high-order standing spin-wave (SSW) modes is about 40 times lower than that for the fundamental one. The observed phenomenon can be explained by considering different features of magnetic anisotropy and exchange fields that, respectively, define the precession frequency for fundamental and high-order SSWs. These results provide further insight into SSWs in iron garnets and may be exploited in many new photomagnonic devices.

Observation of two-critical-angle phenomenon in spin wave resonances in diluted ferromagnetic semiconductor GaMnAs thin films

We have studied surface anisotropy energy and surface pinning parameters of ferromagnetic semiconductor GaMnAs film by analyzing spin wave resonance (SWR) measurements carried out on this material. The SWR spectra were observed in various polar and azimuthal angular orientations of external static magnetic field with respect to crystal axes of an annealed GaMnAs film with a Mn concentration of 8.0 at.%). The observed SWR spectra were interpreted in terms of a recently developed spherical surface pinning (SSP) theory. As predicted by the SSP theory, our data clearly show the existence of two critical angles in specific resonance configurations. The experimental confirmation of this key prediction of the SSP model brings new insights into the behavior of magnetic surface anisotropy of GaMnAs films. In particular, the agreement of our experimental results with SWR theory shows that, by including higher-order terms with cubic symmetry in the description of the surface free energy, our analysis will improve our understandings of the magnetic surface anisotropy of GaMnAs films.

Tunable magnetization dynamics in artificial spin ice via shape anisotropy modification

Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.