Magnetostatic Wave Propagation in a Finite YIG-Loaded Rectangular Waveguide

The nonreciprocal bandpass filter has been achieved by utilizing the nonreciprocity characteristics of the magnetostatic surface wave (MSSW) in planar ferrite slabs. In this article, the dispersion relation, impedance, and attenuation of MSSW between the pure and metallized ferrite slabs have been analyzed and compared. Theoretical analysis indicates that the ferrite slab metallized by a thin conductive layer would introduce significant attenuation on the metallized interface, which is MSSW propagating on the isolated direction, while MSSW on the other surface is barely affected. Therefore, nonreciprocal bandpass filter with enhanced isolation can be achieved with metallized ferrite slab. Simulated S-parameters show that a notch in the isolating direction can be obtained at the passing band of the transmitting direction. Experimental results show that the nonreciprocal filter with metallized yttrium iron garnet (YIG) slab (by depositing 100-nm copper film) exhibits more than 10-dB higher isolation than that with pure YIG slab, while the center frequency, insertion loss, and 3-dB bandwidth maintain almost the same. The center frequency of the filter with metallized YIG slab can be tuned from 7.26 to 8.38 GHz with insertion loss of less than 3 dB, and in-band isolation of more than 30 dB as the dc bias magnetic field is increased from 1.8 to 2.3 kOe. Besides, the nonreciprocal filter has ultra-wide out-band suppression since it utilizes the narrow frequency band of MSSW. The -10-dB out-band rejection exceeds 36 GHz in the upper band and 1 MHz in the lower band.

The satellite ferrimagnetic power limiter : L. J. Varnerin, R. L. Comstock, W. A. Dean and R. W. Kordon, Bell Syst. Tech. J.XLII, 1817 (July 1963)

A new high spatial-resolution magnetic-induction probe that measures microwave magnetic field patterns of magnetostatic waves in ferrite thin films has been developed. The probe’s sensing element is either a strand of 25.4-μm-diam gold wire wrapped around a plastic support or an aluminum rectangular loop photolithographically fabricated on glass. The gold wire method yielded a smallest size of 120 μm, and the aluminum loops achieved a highest resolution of 45 μm. The probe is designed for studies of amplitude profiles, dispersion relations, and phase-propagation direction. Investigations of magnetostatic surface waves (MSSW) and backward volume waves (MSBVW) propagating in liquid-phase epitaxially (LPE) grown yttrium-iron-garnet (YIG) were conducted. The LPE-YIG sample used was 4.5 μm thick with the [111] direction perpendicular to the surface of the sample. MSSW and MSBVW of 2–4 GHz microwave frequency were launched in the LPE-YIG, 4.1° from the [01̄1] direction. Studies of MSSW were done under uniform and nonuniform in-plane magnetic bias fields. When contrasted to expected spreading due to diffraction, MSSW in uniform bias fields were found to ‘‘focus’’ as the wave propagated. The ‘‘focusing’’ effect was determined by measurement of the microwave magnetic field profile, transverse to the phase-propagation direction, as a function of propagation distance. As the MSSW propagated, the peak value of the profile increased while the profile width decreased until a maximum profile amplitude occurred, after which the MSSW decreased in amplitude and the width increased. With MSSW and MSBVW in constant uniform bias fields, direct measure of the wavelengths at various microwave frequencies yielded the dispersion relation for each type of wave. Determination of the dispersion relation of MSBVW confirmed the backward nature of these waves.

Thin films of magnetic garnet materials, e.g. yttrium iron garnet (Y3Fe5O12, YIG), are useful for a variety of applications including microwave integrated circuits and spintronics. Substitution of rare earth ions, such as cerium, is known to enhance the magneto-optic Kerr effect (MOKE) as compared to pure YIG. Thin films of Ce0.75Y2.25Fe5O12 (Ce:YIG) have been grown using the pulsed laser deposition (PLD) technique and their crystal structure examined using high resolution scanning transmission electron microscopy. Homogeneous substitution of Ce in YIG, without oxidation to form a separate CeO2 phase, can be realized in a narrow process window with resulting enhancement of the MOKE signal. The thermally generated signal due to spin Seebeck effect for the optimally doped Ce:YIG films has also been investigated.

The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel's original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel's derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling.

An insulator‐based spin‐thermoelectric (STE) generator is composed of a thin paramagnetic metal (PM: Pt) layer for generating the STE voltage VSTE via the inverse spin Hall effect and a ferrimagnetic insulator (FMI) film or slab used for producing spin‐wave spin currents due to a temperature gradient . Yttrium iron garnet (YIG) is a key material used for the FMI of STE generators. We examined in detail the ferromagnetic resonance (FMR) properties of YIG (Y3Fe5O12), Bi‐substituted YIG (Y3‐xBixFe5O12) and Bi‐ and Al‐substituted YIG (Y3‐xBixFe5‐yAlyO12) films grown by liquid phase epitaxy (LPE). Bi‐substituted YIG films exhibited the large FMR damping and high STE voltage when the films were incorporated in the STE generator. The LPE‐grown Y2.35Bi0.65Fe5O12 film exhibited the FMR linewidth ΔH of 30 mT and the VSTE of 70 μV for the ∇T of . This paper comprehensively presents the origin of the STE generation in the insulator‐based generators on the basis of the results of FMR and STE measurements. To clarify the origin of STE generation in the generators fabricated from single crystal YIG (YIG, Bi‐substituted YIG and Bi‐ and Al‐substituted YIG) films grown by LPE, three principal factors are explained: (a) thermal energy transfer from the phonon system to the spin system, which strengthens the heat excitation of spin precession, through the spin–orbit coupling enhanced by the growth‐induced magnetic anisotropy of LPE‐grown YIG films, (b) in the YIG films incorporated in the STE generators, the generation of spin‐wave spin currents owing its origin to the ferromagnetic spin exchange interaction acting between neighboring spins due to , and (c) how the spin currents pumped into the Pt layer from the YIG film at the Pt/YIG bilayer interface are affected by the magnetization processes of single crystal YIG films. It is concluded that the STE generation of insulator‐based STE generators can be explained from a viewpoint of the spin dynamics under the effect of in the Pt/YIG bilayer structure. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Magneto-optical devices based on Bragg diffraction of light by magnetostatic waves (MSWs) offer the potential of large time-bandwidth optical signal processing at microwave frequencies of 1 to 20 GHz and higher. A thin-film integrated-optical configuration, with the interacting MSW and guided-optical wave both propagating in a common ferrite layer, is necessary to avoid shape-factor demagnetization effects. The underlying theory of the MSW-optical interaction is outlined, including the development of expressions for optical diffraction efficiency as a function of MSW power and frequency, device geometry, materials properties, and other relevant parameters. Recent experimental observations of anisotropic Bragg diffraction and collinear TE↔TM mode conversion induced by MSWs in yttrium iron garnet (YIG) thin films suggest that high-performance MSW integrated-optical devices are feasible. Diffraction levels as large as 4% (7-mm interaction length) and a modulation dynamic range of ∼30 db have been demonstrated. Potential signal processing applications are mentioned, including: spectrum analyzers, convolvers/correlators, deflectors, non-reciprocal optical isolators, and tunable narrowband optical filters. Advantages of these MSW-based devices over the analogous acousto-optical devices include: much greater operating frequencies, tuning through the MSW dispersion relation by varying either the rf frequency or the applied bias magnetic field, simple MSW transducer structures (e.g., a single stripline), and the potential for very high diffraction efficiencies.

The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

An efficient finite-element solution procedure is developed for calculating propagation losses of magnetostatic waves in multilayered inhomogeneous waveguides. The final matrix equation is reduced to a standard complex eigenvalue problem whose eigenvalue corresponds to the complex phase constant itself. Thus, iteration procedures are not necessary and the phase and attenuation constants can be directly obtained by solving a standard eigenvalue equation. The validity of the method is confirmed by calculating propagation losses of magnetostatic surface waves in a single yttrium-iron-garnet (YIG)-film structure. Numerical results for a triple-layered YIG film structure are also presented. It is found that, in the triple-layered structure, propagation losses are highly dependent on the linewidth of the film in which the magnetostatic potential is well confined. >

The use of dynamic magnonic crystals created by a surface acoustic wave (SAW) for measuring the parameters of a surface magnetostatic wave in a film of yttrium iron garnet (YIG) on a gallium gadolinium garnet (GGG) substrate is described. A method for measuring the dispersion characteristics of a surface magnetostatic spin wave (SMSW) and results of such measurements are presented. The method is based on measuring reflected SMSWs at frequencies of forbidden magnonic gaps using the same antenna for the excitation of incident SMSWs and the detection of reflected SMSWs. The attenuation parameter of the SMSW is determined by measuring the frequency width of reflected SMSW signals. The dispersion curves have been measured for several angles between the direction of the magnetic field and the wave vector in the plane of YIG film and for two thicknesses of the YIG film at wave numbers ranging up to 1000 cm–1. Results of measurements of the attenuation parameter are also presented.

Ferrimagnetic echoes have been observed in yttrium iron garnet (YIG) films excited by a microstrip in a magnetostatic surface wave (MSSW) configuration. The design of hyperbolic-shape d magnet pole piec.es, which provide a linear magnetic field gradient along the length of the sample, is discussed. We observe e choes over a 1250 MHz bandwidth (2750 - 4000 MHz) for fixed time delay and fixed magnetic field. The behavior of MSSW echoes is compared with the behavior of backward volume wave echoes in YIG cylinders.

In a slot‐line‐type signal‐to‐noise enhancer for a magnetostatic wave, it is shown theoretically and confirmed experimentally that enhancement can be improved by the symmetric slot‐line structure with yttrium iron garnet (YIG) films on both sides of the slot line and by the layered structure of high permittivity materials. It is shown that the improvement in the amount of enhancement requires an increased attenuation constant of the slot line caused by the conversion loss of the linear operation to the magnetostatic wave. The magnetostatic wave radiation impedance is then derived by recognizing the contribution of the magnetic flux density normal to the slot plane among the electromagnetic field components traveling along the slot line to the conversion of the magnetostatic wave. By means of this radiation impedance, the attenuation constant is derived for the symmetric slot line and the slot line with a high permittivity layered structure so that improvement to enhancement is clarified.

Wave front reversal of surface magnetostatic waves

Bulk Yttrium iron garnet (YIG) has been produced by solid-state reaction with various temperatures. Physical properties of as-sintered YIG are characterized by density test ASTM C-20, XRD, surface morphology with 3D optical microscope and SEM, magnetic properties using SQUID, and XPS Analysis. Samples sintered at 1450 °C have relative density higher than 99%. The Spin Seebeck Effect Voltage output measure by longitudinal configuration under magnetic field±3000 Gauss. The obtained YIG slab of 15 mm x 5 mm x 2.65 mm in size is polished down to 0.5 microns. A 15-nm thick Pt film is deposited by PVD on the whole surface. The slab is wire bonded and connected to a nanovoltmeter to measure its longitudinal spin Seebeck effect voltage (VISHE). The highest measured voltage reaches -0.996 µV/K at ΔΤ=5K and the average of VISHE from the set-up is ±0.805 µV/K for the whole 5 different ΔΤ.

In magnetostatic wave (MSW) resonators based on rectangular yttrium-iron-garnet (YIG) films, straight edges serve as reflectors. In the configuration, width modes are often seen to interfere with the main resonant peak, splitting it. The occurrence of higher width modes is mainly due to the nonuniformity of the internal bias magnetic fields near the corners of the YIG film, leading to a coupling between the principal mode and the higher width mode. To prevent the coupling from occurring, metal films are deposited on both ends of the rectangular YIG film. An experiment on a resonator with metal edge reflectors shows that the resonant peak cannot be split, but that spurious resonances due to undesired higher modes occur. A multibar transducer is used to prevent the excitation of the undesired modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>