Garnet Films Research Articles

Spin Pumping of Magnons Coherently Coupled to a Cavity Dark Mode

Cavity magnonics provides a versatile platform to tune the photon-magnon interaction bringing about promising applications for quantum information processing. Here, we implement a metamaterial planar cavity to suppress the radiative damping by engineering the symmetry of the cavity configuration. Then, the mode with suppressed radiative damping, i.e., dark mode, is coupled to the magnon mode in a thin yttrium iron garnet film ($5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$), which is detected by performing the reflection measurements and spin-pumping experiment. Pronounced anticrossing of the ferromagnetic resonance and the cavity dark mode is observed, where the largest coupling strength reaches 2.5% of the resonant cavity frequency. In addition, the spin wave resonances along the thickness direction are identified, which enhances the spin-pumping signal when they coalesce with the hybridized cavity-magnon-polariton mode. The dark mode excited by the planar metamaterial cavity leads to an improvement in the coherent manipulation of the spin current.

Nonlinear Magnon Polaritons.

We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of a yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent backreaction from the spin waves.

Recent Advances in Yttrium Iron Garnet Films: Methodologies, Characterization, Properties, Applications, and Bibliometric Analysis for Future Research Directions

Due to recent advances in communication systems, dielectric and magnetic ceramics (ferrites) are attractive for use in devices. Spinel-type ferrites were the first material utilized in microwave devices; however, yttrium iron garnet (YIG) has low dielectric losses and is exploited in many applications. Owing to its high Faraday rotation, YIG films are utilized in magneto-optical applications. This study intends to examine the research trends and scientific research progress on highly cited papers discussing YIG films published between 2012 and 2022 using a bibliometric method. A comprehensive review of 100 scientific papers about YIG was performed from the Scopus database. The assessment of these highly cited papers was highlighted based on the following factors: publication trends and performance, limitations/research gaps, keywords, sub-fields, methodology journal evaluations, document type evaluation, issues, difficulties, solutions, and applications as well as guiding future YIG research. The majority of publications (99%) comprise experimental analysis, whereas 1% provide a based state-of-the-art overview. Ninety-one percent of articles focused on magnetization characterization. This bibliometric survey indicates that YIG film research is an expanding and developing field. The results of the data analysis can be utilized to improve the researchers’ understanding of YIG research and to encourage additional study in this area.

The FMR line width and the structure in YIG films deposited by MOD on silicon (1 0 0)

In this work, yttrium-iron garnet (YIG) films deposited on silicon subtract were studied by ferromagnetic resonance (FMR). The samples were prepared by using the Metal-Organic Decomposition (MOD) method on two different thermal treatments (750 °C and 850 °C). The X-ray diffraction suggested the single phase of YIG while atomic force microscopy and scanning electron microscopy reveled film roughness, Rq < 0.2 nm. The FMR measurements showed very different linewidth of 139 Oe for the sample obtained at 750 °C and sample at 850 °C had a smaller linewidth of 93 Oe. The difference was mainly attributed to the different structural ordering of the two samples from the heat treatment at different temperatures.

Delineating magnetization dynamics in solution-processed doped yttrium iron garnet thin films

In this work, thin films of ruthenium-doped and cerium-doped yttrium iron garnet were deposited on silicon using solgel chemistry. Doped YIG could be produced in phase pure form up to a precursor stoichiometry of Y3Ru0.1Fe4.9O12 and Ce0.7Y2.3Fe5O12. Both dopants significantly increase the coercivity and anisotropy field of the materials either due to domain wall pinning or increased spin–orbit coupling from the dopant. To delineate these two effects, the dynamic magnetic properties were studied using strip line ferromagnetic resonance (FMR). The FMR linewidth was separated into intrinsic loss and inhomogeneous line broadening. Inhomogeneous line broadening was found to dominate the magnetic losses in all the films likely due to magnon scattering off grain boundaries, but the Gilbert damping remained fairly low. By comparing the two dopants, it was found that Gilbert damping increased more in Ce:YIG films than in Ru:YIG films. This finding was corroborated by changes in the anisotropy field of the films, indicating a larger contribution from spin–orbit coupling from cerium than from ruthenium. Surprisingly, while magnetic loss globally increased with higher substitution, adding a small amount of dopant actually reduced the inhomogeneous line broadening in both sets of films. This was corroborated by crystallite size. The damping in Ru:YIG also decreased with a small amount of the dopant, which has been predicted by Kittel for doped garnets. Thus, it follows that there is an ideal doping regime where solgel YIG can be doped at low levels without increasing magnetic loss.

Excitation by shot circuited coaxial transducer of magnetostatic modes in rectangular yttrium iron garnet film

The purpose of this work is the study of design of new short-circuited coaxial transducer with thin linear jumper, that circuits on one side of the grounded coaxial cylinder, located above the rectangular iron-yttrium garnet (YIG) film, in homogeneous constant magnetic field with rectangular film along its length or width. The thin linear jumper is directed parallel to the width of the YIG film. Methods. In the CST Microwave Studio environment, an electrodynamic analysis of the model was carried out using the finite element method. To study the efficiency of modes excitation in a ferrite film at different distances between the coaxial transducer and the surface of the YIG film, the frequency dependences of the inverse losses S11 of the model were calculated. Results. 1. The identification of modes in a homogeneous static magnetic field H , directed parallel to the plane of a rectangular YIG film along its width (z-axis) was carried out. 2. The identification of modes in a homogeneous static magnetic field H directed parallel to the plane of the rectangular YIG film along its length (y-axis) was carried out. 3. A comparison of modes spectra was made at H, directed parallel to the plane of the YIG film along its width (z-axis) and length (y-axis). Conclusion. In this paper short-circuited transducer with a thin linear jumper, circuited on one side of the grounded coaxial cylinder, is investigated. By the electrodynamic method distributions of high-frequency magnetic field of the excited magnetostatic modes were calculated and their identification was carried out for two directions of homogeneous static magnetic field H: along width and along length of rectangular YIG film. The dependence of number of excited modes on the distance between a short-circuited transducer and rectangular YIG was also studied. A comparison of modes spectra is carried out at H, directed parallel to the plane of the YIG film along its width and length. With this rotation of vector, the band of effectively excitable modes shifts from 4.6...4.9 GHz to 4.5...4.75 GHz. However, the excitation of these modes in the case of the vector H, directed along the width of YIG film (z-axis), is much more effective in the band 4.65...4.9 GHz than in the case when this vector is directed along the length of YIG film (y-axis). At the same time, excitation of these modes in the case of the vector H, directed along the length of YIG film (y-axis) is effective in the band 4.4...4.6 GHz.

Распространение спиновых волн в каналах, полученных декорированием поверхности пленок железо-иттриевого граната тонкими металлическими областями

Transmission of magnetostatic surface waves (MSSW) through the microchannels formed by decoration of yttrium-iron garnet (YIG) film with non-magnetic (chromium) and ferromagnetic (permalloy) metals having thickness of 30 nm was experimentally studied. MSSW losses induced by the considered metals and MSSW dispersion curves are compared with theoretical dependencies calculated taking into account the finite conductivity and magnetization of the metal layers. Possibility to reach the “antireflective” effect in the amplitude-frequency dependencies of MSSW transmission coefficient with the help of YIG film decoration with the permalloy elements was shown.

Coupling-induced transparency and absorption in a magnon–multiphoton hybrid system

Coupling-induced transparency (CIT) and absorption (CIA) of transmission signals were experimentally observed in a single planar hybrid structure specially designed to consist of a yttrium iron garnet film and three concentric inverted-split-ring resonators (ISRRs). The observation of both CIT and CIA was ascribed to the cooperative effect of the interaction of magnons with three decoupled ISRRs' photon modes and the traveling waves along the microstripline. An analytical model developed based on the balance between the coherent and dissipative multiple-paths interactions precisely reproduced both CIT and CIA experimentally observed from a single hybrid system. This work, promisingly, can provide guidance for the design of efficient, flexible, and well-controllable magnon–photon hybrid devices that are highly in demand for applications to quantum technologies currently under development.

Voltage modulated magnetic anisotropy of rare earth iron garnet thin films on a piezoelectric substrate

Voltage-tuning of magnetic anisotropy is demonstrated in ferrimagnetic insulating rare earth iron garnets on a piezoelectric substrate, (011)-oriented PMN-PT. A 42 nm thick yttrium-substituted dysprosium iron garnet (YDyIG) film is grown via pulsed laser deposition followed by a rapid thermal anneal to crystallize the garnet into ≈5 μm diameter grains. The annealed polycrystalline film is magnetically isotropic in the film plane with total anisotropy dominated by shape and magnetoelastic contributions. Application of an electric field perpendicular to the substrate breaks the in-plane easy axis along [01[Formula: see text]] and an intermediate axis along [100]. The results are explained in terms of the piezoelectric remanent strain caused by poling the substrate, which is transferred to the YDyIG and modulates the magnetoelastic anisotropy.

Antisite Defects and Chemical Expansion in Low‐damping, High‐magnetization Yttrium Iron Garnet Films

AbstractYttrium iron garnet is widely investigated for its suitability in applications ranging from magneto‐optical and microwave devices to magnonics. However, in the few‐nanometer thickness range, epitaxial films exhibit a strong variability in magnetic behavior that hinders their implementation in technological devices. Here, direct visualization and spectroscopy of the atomic structure of a nominally stoichiometric thin film, exhibiting a small damping factor of 3.0 ⋅ 10−4, reveals the occurrence of Y‐excess octahedral antisite defects. The two‐magnon strength is very small, Γ0≈10−6 Oe, indicating a very low occurrence of scattering centers. Notably, the saturation magnetization, 4πMs=2.10 (±0.01) kOe, is higher than the bulk value, in consistency with the suppression of magnetic moment in the minority octahedral sublattice by the observed antisite defects. Analysis of elemental concentration profiles across the substrate‐film interface suggests that the Y‐excess is originated from unbalanced cationic interdiffusion during the early growth stages.

Lock-in thermographic study of spin-wave propagation in magnonic crystals

We have investigated the spin-wave dynamics in a one-dimensional magnonic crystal (MC) with respect to the heat radiation due to the damping of the spin waves. The spin waves were excited by applying microwaves via a wire antenna. The heat induced by the excitation and propagation of spin waves was measured using the lock-in thermography (LIT) technique by periodically modulating the microwave power. The LIT measurements resolved the heat source distributions inside the MC, which is made of an yttrium iron garnet film and periodic grooves with a sub-mm interval, in the backward volume wave geometry. The temperature distribution induced by the spin-wave excitation notably depends on the frequency or wave number of the spin waves, as a result of the formation of rejection bands in the MC. The observed temperature modulation profiles are complicated, but their behavior is consistent with a calculation based on the microwave transmission line approximation of the MCs, demonstrating the applicability of the LIT measurements to the investigation of the spin-wave dynamics in sub-mm scale MCs.

Development of Tb1.5Gd1.5Al5O12:Ce Single-Crystalline Film Converters for WLED Using a Liquid Phase Epitaxy Growth Method

The investigation of the structural, luminescent and photoconversion properties (color coordinates, correlated color temperature, color rendering index and luminous efficacy) of the single-crystalline films of Ce3+-doped Tb1.5Gd1.5Al5O12:Ce mixed garnet with variable film thickness was performed in this work. These film converters were grown on undoped Y3Al5O12 substrates using the liquid phase epitaxy technique. When combined directly with blue LEDs that were commercially available in the market, the developed garnet film converters were responsible for producing white light. The trend line on the color coordinate diagram was obtained for the first time for the Tb1.5Gd1.5Al5O12:Ce converters with the systematic variation in film thickness in the range of 45–82 µm. Under 464 nm blue LED excitation, the investigated converters with a thickness of 55 µm resulted in an ideal white color.

Magnetic Domain Structure of Lu2.1Bi0.9Fe5O12 Epitaxial Films Studied by Magnetic Force Microscopy and Optical Second Harmonic Generation

Magnetic structure of functional magnetic dielectrics is traditionally of high interest. Here, we use the magnetic force microscopy (MFM) and nonlinear-optical probe of second harmonic generation for studies of surface domain structure of monocrystalline Lu2.1Bi0.9Fe5O12 garnet films. The transformation of the magnetic domains under the application of the dc magnetic field is revealed by the MFM for both the top-view and the cleavage of the iron-garnet layer. Complementary magnetic force and second harmonic generation microscopy show that the considered film reveals the magnetization inclined with respect to the film’s normal, with its orientation being inhomogeneous within the film’s thickness. The second harmonic generation (SHG) microscopy confirms the zigzag structure of the surface-closing domain with the magnetization containing in-plane and out-of-plane magnetization components. We believe that these features of magnetic behavior of garnet films are important for the design of garnet-based magnetic devices.

Terahertz-driven magnetization dynamics of bismuth-substituted yttrium iron-gallium garnet thin film near a compensation point

Magnetization dynamics of bismuth-substituted yttrium iron-gallium garnet film $({\mathrm{Y}}_{3\ensuremath{-}z}{\mathrm{Bi}}_{z})[{\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}][{\mathrm{Fe}}_{3\ensuremath{-}y}{\mathrm{Ga}}_{y}]{\mathrm{O}}_{12}$ has been studied using a terahertz pump--optical probe spectroscopy. Two magnetic modes are observed whose frequencies intersect at a magnetization compensation point. The experimental dependence of the excited modes on terahertz pulse polarization, an external magnetic field and the temperature are analyzed. The theoretical description based on symmetry and the Lagrangian formalisms is proposed. Magnetic modes crossing is explained as interplay between exchange and anisotropy energies equally contributing near the compensation point. Simulations based on the Landau-Lifshitz-Gilbert equations show that a difference in magneto-optical susceptibilities of tetrahedral and octahedral iron sublattices can substantially enhance the sensitivity to the magnetic modes.

Structural distortion induced enhancement of magnetic and dielectric properties in Pr modified yttrium iron garnet films

Low saturation magnetization and low dielectric constant significantly limited the application of Yttrium iron garnet (Y3Fe5O12, YIG) film, which could be enhanced through structural distortion. In this work, Y3-xPrxFe5O12 (YPrxIG) films were fabricated using chemical solution deposition method. The substitution of Pr3+ for Y3+ was adopted to regulate the symmetry of its polyhedron to induce a structural distortion owing to a larger ion radius of Pr3+ than that of Y3+. YPr0.20IG film exhibited a higher saturation magnetization of 241.2 emu/cm3 than the pure YIG film owing to the enhanced super-exchange from the increased FeO–O-FeT bond angle. The dielectric constant of YPr0.20IG film increased to 22.4 at 12.4 GHz, which was the contribution of electron polarization and ion polarization of Fe2+. The band gap value of YPr0.20IG film was reduced to 2.80 eV. These could be physically clarified that the electrons between Fe2+ and Fe3+ turned to migrate from the valence band to the conduction band.

Concept of the Optomagnonic Logic Operation

We present the concept of the optomagnonic logic gate, where interference of spin waves excited by femtosecond laser pulses at multiple points by the inverse Faraday effect in a bismuth-substituted yttrium iron garnet film plays a decisive role. The resulting spin-wave distribution is determined by constructive and destructive interference, which is controlled by the polarization of laser sources. A variable platform with a spatial light modulator is used to control the overall spin-wave distribution by manipulating the arrangement of the local spin-wave sources. We demonstrate the experimental optical excitation of backwards volume magnetostatic spin waves at multiple points and use wavelet analysis and micromagnetic numeric simulations to analyze them. Simulations provide an excellent agreement with the experimental data and are further used to model the magnon logical gate (xnor) based on optically excited spin-wave interference.

Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning

Thin garnet films are becoming central for magnon-spintronics and spin-orbitronics devices as they show versatile magnetic properties together with low magnetic losses. These fields would benefit from materials in which heat does not affect the magnetization dynamics, an effect known as the non-linear thermal frequency shift. In this study, low damping Bi substituted Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser Deposition. Through a fine tuning of the growth parameters, the precise control of the perpendicular magnetic anisotropy allows to achieve a full compensation of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as the only tuning parameter induces the easy-axis to go from out-of-plane to in-plane. For films that are close to the dipolar compensation, Ferromagnetic Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$ that has almost no temperature dependence over a large temperature range (260 K to 400 K) resulting in an anisotropy temperature exponent of 2. These findings put Bi:YIG system among the very few materials in which the temperature dependence of the magnetic anisotropy varies at the same rate than the saturation magnetization. This interesting behavior is ascribed phenomenologically to the sizable orbital moment of $Bi^{3+}$.

Confinement of Bose–Einstein magnon condensates in adjustable complex magnetization landscapes

Coherent wave states such as Bose–Einstein condensates (BECs), which spontaneously form in an overpopulated magnon gas even at room temperature, have considerable potential for wave-based computing and information processing at microwave frequencies. The ability to control the transport properties of magnon BECs plays an essential role in their practical use. Here, we demonstrate the spatiotemporal control of the BEC density distribution through the excitation of magnon supercurrents in an inhomogeneously magnetized yttrium iron garnet film. The BEC is created by microwave parametric pumping and probed by Brillouin light scattering spectroscopy. The desired magnetization profile is prepared by heating the film with optical patterns projected onto its surface using a phase-based wavefront modulation technique. Specifically, we observe a pronounced spatially localized magnon accumulation caused by magnon supercurrents flowing toward each other originating in two heated regions. This accumulation effect increases the BEC lifetime due to the constant influx of condensed magnons into the confinement region. The shown approach to manipulate coherent waves provides an opportunity to extend the lifetime of freely evolving magnon BECs, create dynamic magnon textures, and study the interaction of magnon condensates formed in different regions of the sample.

Low‐Damping Spin‐Wave Transmission in YIG/Pt‐Interfaced Structures

AbstractMagnetic heterostructures consisting of single‐crystal yttrium iron garnet (YIG) films coated with platinum are widely used in spin‐wave experiments related to spintronic phenomena such as the spin‐transfer‐torque, spin‐Hall, and spin‐Seebeck effects. However, spin waves in YIG/Pt bilayers experience much stronger attenuation than in bare YIG films. For micrometer‐thick YIG films, this effect is caused by microwave eddy currents in the Pt layer. This paper reports that by employing an excitation configuration in which the YIG film faces the metal plate of the microstrip antenna structure, the eddy currents in Pt are shunted and the transmission of the Damon–Eschbach surface spin wave is greatly improved. The reduction in spin‐wave attenuation persists even when the Pt coating is separated from the ground plate by a thin dielectric layer. This makes the proposed excitation configuration suitable for injection of an electric current into the Pt layer and thus for application in spintronics devices. The theoretical analysis carried out within the framework of the electrodynamic approach reveals how the platinum nanolayer and the nearby highly conductive metal plate affect the group velocity and the lifetime of the Damon–Eshbach surface wave and how these two wavelength‐dependent quantities determine the transmission characteristics of the spin‐wave device.

Magneto-optical Intensity Modulation for Optical Vortex Beams with Orbital Angular Momentum

Here we theoretically and experimentally demonstrate a way to control the intensity of optical vortices by a magnetic field directed along the beam axis. We describe the principle of an optical vortex modulator and switch based on the Faraday effect in an iron garnet film. Importantly, the magnetic field influences only the polarization plane of the vortex and keeps its topological charge.