Magnetostatic Surface Wave Propagation Research Articles

Investigation of the interference of magnetostatic surface waves using the inverse spin Hall effect

The effect of EMF generation due to the inverse spin-Hall effect during the propagation of magnetostatic surface waves (MSSW) in the structure of yttrium iron garnet (YIG) --- platinum based on a two-layer YIG film with different saturation magnetizations of the layers ((4π M1>4π M2) has been experimentally studied. It was shown that the magnitude of the EMF resonantly increases at the frequencies of hybridization of the MSSW with the exchange modes of the structure. At the same time, at the frequencies of the MSSW of the layer with a higher magnetization, oscillations of the EMF are observed, caused by its hybridization with the exchange modes of both the layer with 4π M1 and the layer with lower magnetization, which indicates the influence of interlayer exchange on the efficiency of spin pumping in the structure under consideration. The influence of the interference of counterpropagating MSSWs on the generated EMF has been studied. It has been shown that the EMF value is sensitive to the phase difference between counterpropagating MSSWs and oscillates. In this case, the amplitude of the oscillations is determined by the ratio of the wavelength of the MSSW and the length of the platinum film. Keywords: magnetostatic waves, yttrium iron garnet, platinum, interference, inverse spin Hall effect.

Spectrum evolution of magnetostatic waves excited through ultrafast laser-induced heating

We study experimentally the influence of the laser-induced temperature gradient on the parameters of propagating magnetostatic surface waves in thin film of the ferromagnetic metallic alloy Galfenol Fe0.81Ga0.19. The material has a pronounced magnetocrystalline anisotropy and exhibits the long-distance propagation of magnetostatic surface waves excited with femtosecond laser pulses. The excitation pulse heats up the sample locally, what leads to the spatial-temporal change of magnetization and anisotropy parameters of the film, and thus excites the magnetostatic surface waves. We show experimentally that the spectrum of the excited waves narrows as they propagate in such a gradient medium. By changing the orientation of external magnetic field with respect to anisotropy axes of the sample, we control whether the low- or high-frequency part of the spin waves spectrum is suppressed.

Defect Modes Control in Coupled Magnonic Crystals

We report on the theoretical study of magnetostatic surface wave propagation through the two side-coupled 1-D magnonic crystals (MCs) with broken translational symmetry. Using the transfer matrix method, we obtained transmission and reflection coefficients. Existence of two defect modes in such four-port planar structure was shown. We consider the possibility of controlling the position of defect modes by changing coupling between MCs. Comparison between investigated structure with coupled defect-free magnonic crystals was provided.

Enhanced Nonreciprocity of Magnetostatic Surface Waves in Yttrium-Iron-Garnet Films Deposited on Silicon Substrates by Ion-Beam Evaporation

Propagation of magnetostatic surface waves (MSSW) in yttrium-iron-garnet films deposited by ion-beam evaporation on silicon substrates and consisting of two layers—the buffer layer and the main layer—was studied. It is shown that exchange coupling and surface spin pinning at the interface of the main and buffer layers can enhance nonreciprocity of MSSW propagation and can result in the appearance of anomalous regions in the dispersion curves caused by spin-wave resonances across the film thickness.

Magnetostatic Surface Wave Dispersion and Losses in an Yttrium-Iron Garnet Film With a Subwavelength Periodic Structure

Magnetostatic surface wave propagation was measured in an yttrium-iron garnet film with a subwavelength, micrometer-sized, periodic array of etched grooves. There were regions with anomalous dispersion and rejection bands in the frequency dependence of the transmission characteristic. Their number and bandwidth changed depending on the angle between the directions of the bias magnetic field and the grooves.

Neighboring-Metallic-Layer-Induced Nonreciprocal Wave Propagation in a Thin Metallic Ferromagnetic Film

Nonreciprocal spin wave propagation, induced by placing a neighboring metallic nonmagnetic layer, has been studied in metallic ferromagnetic thin films. The structure consists of a set of coupled microstrip transmission lines acting as antennas placed over a thin Ni80Fe20 layer. Nonreciprocal propagation of magnetostatic surface waves (MSSWs) has been observed. The nonreciprocal effect is evaluated by the amplitude ratio and the phase difference of the MSSWs traveling in opposite directions. By investigating the correlation between the device structure and the nonreciprocal effects, a maximum of −26.0 dB of the amplitude ratio and −180.0° phase difference were obtained. These results can be applied to optimize the nonreciprocal device.

Nonreciprocal Oersted field contribution to the current-induced frequency shift of magnetostatic surface waves

The influence of an electrical current on the propagation of magnetostatic surface waves is investigated in a relatively thick (40 nm) permalloy film both experimentally and theoretically. Contrary to previously studied thinner films where the dominating effect is the current-induced spin-wave Doppler shift, the magnetic field generated by the current (Oersted field) is found to induce a strong non-reciprocal frequency shift which overcompensates the Doppler shift. The measured current induced frequency shift is in agreement with the developed theory. The theory relates the sign of of the frequency shift to the spin wave modal profiles. The good agreement between the experiment and the theory confirms a recent prediction of a counter-intuitive mode localization for magnetostatic surface waves in the dipole-exchange regime.

Magnetostatic surface waves propagation at dissipative ferrite-MTMs-metal structure.

The magnetostatic surface waves (MSSW) propagation in a layered structure composed of ferrite film covered by air and on top of metamaterial (MTM) placed on metal is discussed. Dispersion equations which relate the parameters of different layers are derived and used to analyse propagation of MSSW. It is found that the MSSW excitation band depends on the thickness of the MTM layer and ferrite layer.

Spin pumping by nonreciprocal spin waves under local excitation

We measured spatial distribution of spin pumping by nonreciprocal magnetostatic surface waves (MSSWs) using inverse spin Hall effect (ISHE) in a YIG/Pt system under local excitation. The local intensity of spin pumping by MSSWs shows center displacement of ± 0.1 mm from the center of a waveguide according to the reversal of a bias field, which is due to the nonreciprocal propagation of MSSWs over a macroscopic distance. The combination of spin pumping and ISHE enables electrical investigation of local spin dynamics in a magnetic insulator.

Magnetostatic surface wave propagation in a one-dimensional magnonic crystal with broken translational symmetry

Magnetostatic surface wave propagation through the one-dimensional magnonic crystal with broken translational symmetry developed in an yttrium iron garnet film was experimentally studied. Magnonic crystals were prepared in the form of lattices of etched grooves in yttrium iron garnet film where structural defect was inserted in the center of the lattice in the form of a single defective crest or groove with the width different from those in the lattices. The defect modes within the magnonic bandgaps were detected under conditions corresponding to excitation of the Bragg reflecting resonator formed by the defect.

Green’s function for magnetostatic surface waves and its application to the study of diffraction patterns

This paper presents the two-dimensional (2D) Green's function (GF) of magnetostatic surface waves (MSSWs) in real space and the frequency domain, i.e., the spatial propagation pattern of MSSWs emitted by a point wave source in a tangentially magnetized slab geometry, including the effect of finite damping. The theory first derives an inhomogeneous differential equation of the spin system under a magnetostatic approximation. This equation is translated into a Sturm-Liouville problem by introducing a Hermitian operator, and solved by the eigenfunction expansion technique, which yields an integral expression of the GF in the form of a 2D inverse Fourier transform. The obtained GF demonstrates various features characteristic of MSSWs, such as strongly anisotropic propagation, angular confinement of energy flow from the wave source whose limit angle is defined as the critical angle for the group velocity ${\ensuremath{\theta}}_{g}$, and semicaustic beams along ${\ensuremath{\theta}}_{g}$. We then calculate the 1D spatial profiles and 2D diffraction patterns of MSSW propagation by convolving the GF with various wave source distributions, and compare them with experimental results observed on a tangentially magnetized Permalloy film. Comparison between these numerical and experimental results shows excellent agreement.

Propagation of magnetostatic surface waves in a ferrite plate magnetized by a spatially periodic transverse field

Propagation of magnetostatic surface waves (MSSWs) in a ferrite plate magnetized by a spatially periodic transverse field has been considered. The parameters of MSSW propagation have been calculated by the Hamilton-Auld method. It is shown that only noncollinear MSSWs, whose wave-beam trajectories as well as wave numbers and angles, which determine the directions of the vectors of the phase and group velocities, are described by functions that are periodic in the direction of the wave propagation, can exist in this field. The period of these functions is determined by the period of the spatially periodic field. The frequency range of existence of the collinear waves is narrower than that of the waves in a uniformly magnetized plate. The characteristics of wave propagation in a nonuniform spatially periodic field are compared to the characteristics of wave propagation in nonuniform fields of known types.

Characteristics of the electromagnetic radiation resulting from arbitrarily directed propagation of magnetostatic surface waves in an increasing transverse magnetic field

Radiation of the electromagnetic waves accompanying propagation of a magnetostatic surface wave with nonparallel directions of the phase and group velocities in a ferrite slab magnetized in its plane by a transverse linearly increasing magnetic field is analyzed using the model of accelerated motion of magnetic charges. It is shown that, at each point of the space surrounding the ferrite slab, the shape of the radiation pattern strongly depends on the angle between the direction perpendicular to the direction of propagation of the magnetic field and the direction of the wave vector of the magnetostatic surface wave.

Propagation of Magnetostatic Surface Waves in a Tunable One-Dimensional Magnonic Crystal

We have studied propagation of magnetostatic surface waves in yttrium iron garnet films with attached 1D periodic arrays of metal strips. For different experimental geometries and different designs of 1D periodic arrays of metal strips, propagation spectra of magnetostatic surface waves were measured and analyzed. We have shown a way to control propagation characteristics of magnetostatic surface waves by changing of electrical contact between periodic metal strips.

Magnetostatic surface waves in a ferrite/dielectric/metal structure magnetized by a linearly increasing transverse field

Propagation of magnetostatic surface waves (MSSWs) in a ferrite/dielectric/metal structure magnetized by a nonuniform field whose intensity linearly increases with the coordinate normal to the direction of the magnetic field is considered. Wave trajectories are calculated. The variation of the wave number, as well as the variations of the directions of the phase- and group-velocity vectors, is investigated. Possible transformations of some waves into other modes and conditions for MSSW radiation are formulated. The parameters of ferrite/dielectric/metal structures that can be used in backward-wave devices are determined.

Numerical analysis of nonlinear magnetostatic wave propagation by finite-element method

Transmitted power dependence of magnetostatic surface-wave propagation has been numerically investigated with the help of the finite-element method. The solutions in the weakly-nonlinear regime are compared and shown to be in good agreement with the results from the quasi-linear approximation in conventional perturbation methods. In addition, the power dependence of the propagation constants is also shown in the strongly nonlinear regime.

The propagation of magnetostatic surface waves in ferrite/superconductor structures

An electrodynamic model that describes the dispersion of magnetostatic surface waves in ferrite/superconductor structures is suggested. On its basis, a new approach to determining the microwave sheet resistance RS of superconducting films in a magnetic field is elaborated. The values calculated (RS=0.20–0.96 mΩ) agree with results obtained by the Tauber method. For YIG/YBCO structures, the controllable phase shift is about 1.5π when the depth of magnetostatic wave penetration into the YBCO film varies from 2.0 to 0.8 µm.

Stochastic instability of the magnetostatic surface wave trajectories in a ferrite film magnetized by a modulated field with a banklike profile

We report on the previously unstudied stochastic process arising when a magnetostatic surface wave (MSSW) propagates in a ferrite film magnetized by a modulated periodic inhomogeneous field with a banklike profile. The shape of the MSSW trajectories and the phase portrait of the stochastic process were established. It is shown that the MSSW trajectory becomes unstable and terminates when the MSSW propagation angle exceeds the cutoff angle.

Spatial distribution of the electromagnetic radiation accompanying propagation of magnetostatic surface waves in a ferrite film magnetized by a transversely nonuniform field

A model is proposed for description of the spatial distribution of electromagnetic waves (EMWs) generated during the propagation of magnetostatic surface waves (MSSWs) in a ferrite film (FF) magnetized by a transversely nonuniform field. The EMW radiation pattern calculated using this model has two lobes mutually symmetric relative to the FF plane. The lobes are tilted in the direction of MSSW propagation, the tilt increasing with the MSSW velocity approaching the velocity of EMW in the film. The calculated results are in good qualitative agreement with experiment.

Relaxation of the magnetostatic wave absorption in the ferrite-semiconductor structure

In this paper, the results of the theoretical studies of magnetostatic surface wave (MSSW) propagation in layer-photosensitive semiconductor-ferrite waveguides when the external electromagnetic wave affects the semiconductor surface are reported. Dispersion relation of MSSW has been found and the effects of various intensities of electromagnetic wave on the propagation characteristics have been examined. It has been shown that MSSW propagation loss can decrease and there is a frequency band in which MSSW has amplification with increasing intensity of the external light.