YIG Films Research Articles

Optimizing spin pumping in Yttrium Iron Garnet/Platinum bilayers under varying oxygen pressure

Here, we study the influence of magnetic properties on the spin-pumping effect of the Yttrium Iron Garnet/Platinum (YIG/Pt) bilayer. YIG films were deposited by pulsed laser deposition under variable oxygen pressures. Using broadband ferromagnetic resonance techniques, the magnetic properties of the YIG films were measured. We analyzed the spin-pumping effect in these films by measuring damping changes in samples with and without Pt layers, enabling the calculation of spin-mixing conductance. Experimental results show that films prepared at high oxygen pressure exhibit lower magnetization and reduced spin pumping, αsp, leading to a decreased spin mixing conductance, g↑↓. We report a variation in g↑↓ ranging from 4.2×1018 to 15.6×1018,m−2. These findings underscore the sensitivity of spin transport properties to deposition parameters in YIG-based spintronic devices.

Thermomagnetic recording of highly Bi-substituted iron garnet film using scanning laser for spatial light modulation

Spatial light modulations (SLM) utilizing the magneto-optical (MO) effect of magnetic materials are expected to offer fast switching and small pixel sizes as small as the wavelength of the light. However, the small MO effect is a major issue. In this paper, we report a thermomagnetic recording of highly bismuth-substituted garnet film, known for large Faraday effects. Y0.5Bi2.5Fe4GaO12 (Bi,Ga:YIG) film with a Faraday rotation of −4.66 degrees was used as an MO medium. A laser scanning thermomagnetic recording system using a Galvanometer mirror was developed and the size and quality of recorded magnetic domains were investigated. The smallest recorded magnetic domain diameter was 0.62 μm with a small standard deviation of 0.09 μm. Line patterns with a width of 1 μm can be recorded in this film. We found that Bi,Ga:YIG films have potential as a material for SLMs with fast switching, submicron pixel size, and large MO effect.

Low Gilbert damping in Bi/In-doped YIG thin films with giant Faraday effect

Abstract Magnetic films with low Gilbert damping are crucial for magnonic devices, which provide a promising platform for realizing ultralow-energy devices. In this study, low Gilbert damping and coercive field were observed in Bi/In-doped yttrium iron garnet (BiIn:YIG) thin films. The BiIn:YIG (444) films were deposited onto different substrates using pulsed laser deposition. Low coercivity (<1 Oe) with saturation magnetization of 125.09 emu/cc was achieved along the in-plane direction of BiIn:YIG film. The values of Gilbert damping and inhomogeneous broadening of ferromagnetic resonance in BiIn:YIG films were obtained to be as low as 4.05 × 10−4 and 5.62 Oe, respectively. In addition to low damping, the giant Faraday rotation angles (up to 2.9 × 104 deg/cm) were also observed in the BiIn:YIG film. By modifying the magnetic structure and coupling effect between Bi3+ and Fe3+ of Bi:YIG, doped In3+ plays a key role on variation of the magnetic properties. The low damping and giant Faraday effect made the BiIn:YIG film an appealing candidate for magnonic and magneto-optical devices.

Acoustically driven ferromagnetic resonance in YIG thin films

Acoustically driven ferromagnetic resonance (ADFMR) is a platform that enables efficient generation and detection of spin waves via magnetoelastic coupling with surface acoustic waves (SAWs). While previous studies successfully achieved ADFMR in ferromagnetic metals, there are only few reports on ADFMR in magnetic insulators such as yttrium iron garnet (Y3Fe5O12, YIG) despite more favorable spin wave properties, including low damping and long coherence length. The growth of high-quality YIG films for ADFMR devices is a major challenge due to poor lattice-matching and thermal degradation of the piezoelectric substrates during film crystallization. In this work, we demonstrate ADFMR of YIG thin films on LiNbO3 (LNO) substrates. We employed a SiOx buffer layer and rapid thermal annealing for crystallization of YIG films with minimal thermal degradation of LNO substrates. Optimized ADFMR device designs and time-gating measurements were used to enhance the ADFMR signal and overcome the intrinsically low magnetoelastic coupling of YIG. YIG films have a polycrystalline structure with an in-plane easy direction due to biaxial stresses induced during cooling after crystallization. The YIG device shows clear ADFMR patterns with maximum absorption for H ≈ 160 mT parallel to SAW propagation, which is consistent with our simulation results based on existing theoretical models. These results expand possibilities for developing efficient spin wave devices with magnetic insulators.

Preparation of BaTiO3/Y3Fe5O12 bilayers and their ferroelectric/magnetic properties

The converse magnetoelectric effect in the ferroelectric/ferrimagnetic bilayers shows a great promise for realizing energy efficient, dense, and fast information storage and processing. In this study, we prepare the hybrid structures consisting of a ferroelectric layer BaTiO3 (BTO) and a ferrimagnetic insulator layer Y3Fe5O12 (YIG) via magnetron sputtering technique and post-annealing procedure. A visible ferroelectricity hysteresis loop for the BTO film and an apparent magnetic hysteresis loop for the YIG film are obtained. Moreover, by capping a platinum layer on the hybrid structures and performing longitudinal spin Seebeck measurements, a detectable spin-charge conversion voltage is observed, and even significant manipulation of this conversion in BTO/YIG/Pt trilayers is achieved by electrical means. These results show great potential for the development of tunable YIG-based devices and are instructive for future artificial multiferroic heterostructures devices applications.

Waveguide modes of exchange spin waves in epitaxial YIG films

It has been shown that exchange spin wave (ESW) waveguide modes can be excited in epitaxial ferrite films. This is facilitated by the presence of a thin transition layer at the interface between the ferrite film and the non-magnetic substrate. A method for calculating the dispersion and energy characteristics of ESW waveguide modes is proposed. It is shown that the propagation of ESW modes is accompanied by the transfer of exchange power in the plane of the film. As the wave numbers increase indefinitely, the dispersion of the ESW modes asymptotically approaches the quadratic dispersion law. At zero wave numbers, the frequencies of the ESW modes coincide with the frequencies of uniform spin wave resonances. The possibility of crossing the dispersion branches of different ESW modes is demonstrated, which indicates the possibility of intermodal magnon-magnon hybridization.

Spin thermoelectric and spin transport in YIG films fabricated by chemical method

Spin transport in heterojunctions between magnetic insulators and heavy metals has garnered significant attention due to its potential in spintronics applications. In this study, we employed the metal-organic decomposition (MOD) method to fabricate high-quality yttrium iron garnet (Y3Fe5O12-YIG) films on (111)-oriented gadolinium gallium iron garnet (Gd3Ga5O12-GGG) substrate. We conducted a thorough characterization of the crystallinity, surface morphology, and magnetic properties of the YIG films at various thicknesses. The obtained samples exhibited smooth surfaces with roughness mean-square (RMS) below 0.6 nm. Epitaxial growth was maintained for films up to 116 nm in thickness but deteriorated beyond that. The magnetic anisotropy demonstrated an easy axis in the in-plane direction, accompanied by a low coercivity of 4.8 ± 0.4 Oe. The spin Seebeck effect voltage measurement shows the highest signal for 366 nm thick film and is reduced if the thickness increases. Furthermore, we investigated spin transport across the YIG/Pt interface using spin Hall magnetoresistance. The average spin-mixing conductance (Gr) was determined to be 5.79 ± 0.54 × 1014 Ω−1m−2, a value comparable to those reported in previous studies.

Crystallization of Y3Fe5O12 thin films on silicon photonic waveguides using CO2 laser annealing

We report the local crystallization of Y3Fe5O12 (YIG) thin films grown on Si substrates, and SOI waveguides by CO2 laser annealing (LA). The effect of laser power and oxygen pressure on the crystal structure of YIG films was systematically studied. Laser power dominated the YIG film crystallinity, while oxygen partial pressure during LA strongly influenced the crystal grain size and magnetic anisotropy. Fully crystallized YIG thin films with pure garnet phases were fabricated by LA. The refractive index n and extinction coefficient k were comparable to thin films fabricated by rapid thermal annealing (RTA). Propagation loss measured at 1550 nm wavelength on YIG/SOI waveguides and YIG/SiN ring resonators were comparable to RTA annealed films, promising device development for silicon photonics.

Manipulation of energy-resolved magneto–optical effect in yttrium iron garnet films achieved by covering with nonmagnetic metals

The effect of the interface-driven magnetic optical (MO) manipulation on Pt/Yttrium iron garnet (YIG) and Cu/YIG has been investigated using energy-resolved magnetic circular dichroism (ER-MCD) system. By mapping the spatial MCD at different excitation energies, the results indicate manipulation of the spin-polarized electronic structure of YIG through interface charge transfer. Specifically, compared to the Cu/YIG region, we found that the Pt/YIG region exhibited a higher level of MCD enhancement and even a pronounced MCD sign inversion at certain excitation energies. In contrast, the saturation moment of the Pt-covered YIG film decreased significantly, while the enhancement was only slight for the Cu-covered YIG film. Based on the first-principles calculations, the presence of distinct polarized interface states of tetrahedral Fe ions in metal/YIG systems results in conflicting observations regarding optical and magnetic proximity effects. We present evidence that ER-MCD can effectively reveal dominant spin-polarized optical transitions in ferrimagnetic (FIM) materials, providing direct access to the polarized interface states in the nonmagnetic metal (NM)/FIM heterosystem. This capability opens opportunities to manipulate and customize the magneto–optical effect with energy resolution for various applications in magneto-optics.

Pure Spin Transport in YIG Films with Amorphous‐to‐Crystalline Transformation

AbstractMagnetic insulators, especially Y3Fe5O12 (YIG), are considered promising candidates for spin‐based device applications due to their ultralow damping, high spin injection efficiency, and long‐distance spin propagation. However, these intriguing features are widely studied based on crystallization YIG films. Pure spin phenomena, like spin transport in YIG films with structural evolution, remain unclear. Herein, pure spin transportation is systematically investigated in the sandwich structure formed by YIG, the inserted layer‐nominal YIG (n‐YIG) with a varied crystalline structure and heavy metal Platinum (Pt). By applying ferromagnetic resonance (FMR)‐driven inverse spin Hall effect (ISHE) measurement, the detected ISHE voltage signal presented a strong correlation with the thickness of n‐YIG and its crystalline phase. A significant increasement in spin transportation is obtained for the crystallized n‐YIG via a high‐temperature annealing. These results demonstrate that pure spin current is transported availably in the structural evolution of YIG films. Furthermore, the element‐specific X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD) spectra on the n‐YIG films showed a distinction for the crystallized n‐YIG which indicates that the spin propagation is correlated to its magnetic order. These findings are instructive for low‐dissipation spin‐based devices.

Reciprocal and non-reciprocal electromagnetic wave propagation in sub-100 nm epitaxial YIG thin films deposited under different oxygen growth pressure

Directional dependent transport of information in magnetic thin films offers a great opportunity to realize reciprocal and nonreciprocal microwave devices, such as filters, phase shifter, isolators and circulators. Electromagnetic wave (EM) propagation in sub-100 nm thin magnetic film is critical, yet reciprocal and non-reciprocal wave propagation and its accurate measurements remain a challenge. We investigated reciprocal and non-reciprocal wave propagation in 90 nm thick epitaxial thin films of yttrium iron garnet (Y3Fe5O12:YIG) grown by pulse laser deposition (PLD) technique on gadolinium gallium garnet [GGG(100)] substrates. The effect of oxygen growth pressure during deposition of YIG films exhibit directional dependence properties of electromagnetic wave propagation. The reciprocal EM wave propagation was generated by a S-type transmission line to achieve microwave (RF) magnetic fields (hRF) perpendicular to applied dc magnetic fields (HDC), to ensure the ferromagnetic resonance (FMR) condition. The center frequency is tuned up to 20 GHz with an applied magnetic field of 6 kOe. The tuning of the center frequency was achieved as of 85.3 % with HDC of 6 kOe. To achieve non-reciprocal EM-wave propagation one straight microstrip line was used to ensures a parallel configuration (parallel pumping FMR condition) of hRF to HDC. The nonreciprocity observed is due to the presence of gyrotropic properties in the YIG thin films and it enhances when YIG film was placed in asymmetric geometry. Further, oxygen growth pressure (>0.1 mbar) grown YIG films enhances the nonreciprocity by 21.6 %. The experimental results were successfully validated using high-frequency structure simulator (HFSS). Hence, these results indicate that controlled deposition parameters can be a crucial parameter in the design of reciprocal and nonreciprocal microwave signal processing devices.

Pass bands formation in YIG film with periodic metal grating

Experimental results on the magnetostatic surface wave (MSSW) propagation in an yttrium-iron garnet film with a periodical array of metal stripes on the surface are presented. An effect of the pass bands formation in the MSSW transmission characteristics contrasting to the known Bragg stop bands inherent in a periodical structure is reported and discussed. Our findings provide one more way to affect the spin wave propagation and realize a control in magnonic devices.

Spin‐Thermoelectric Generation of Insulator‐Based Generators Incorporating a Single‐Crystal Yttrium Iron Garnet Film in Relation to Domain Magnetization Processes

Normalized VSTE–H loops measured for generators fabricated from LPE‐grown yttrium iron garnet Y3–xBixFe5O12 (YIG/Bi:YIG) films agree well with the normalized M–H curves observed for those films by using a vibrating sample magnetometer. VSTE and M are the spin‐thermoelectric (STE) voltage and the YIG/Bi:YIG magnetization depending on an external field H, respectively. The coincidence between VSTE–H loops and M–H curves indicates that VSTE strongly depends on the magnetic property of ferrimagnetic insulator YIG films incorporated in STE generators. We try explaining the STE generation with VSTE–H loops from a viewpoint of domain magnetization processes in single‐crystal YIG/Bi:YIG films grown by liquid phase epitaxy (LPE). We exemplify that our idea about the fundamental mechanism of STE generation in an insulator‐based generator also well explains the mode of spin waves generated under a temperature gradient ∇T parallel to a plane of Pt/YIG bilayer interface. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Vacuum laser annealing of magnetooptical cerium-substituted yttrium iron garnet films

Laser annealing in a vacuum chamber was employed to achieve the selective crystallization of a cerium-substituted yttrium iron garnet (Ce:YIG, Ce1Y2Fe5O12) film on a glass substrate. The film was selectively crystallized using a continuous-wave laser, and the transmissivity, optical constants, electronic binding states, magnetic properties, and magnetooptical properties of the fabricated Ce:YIG films were measured. A single Ce:YIG phase was observed using X-ray diffraction, and the film's magnetization was comparable to that of Ce:YIG prepared by heater annealing. Faraday rotation angles of 0.50°/μm and −0.25°/μm were obtained at wavelengths of 532 nm and 1064 nm, respectively.

Magnon Confinement in an All-on-Chip YIG Cavity Resonator Using Hybrid YIG/Py Magnon Barriers.

Confining magnons in cavities can introduce new functionalities to magnonic devices, enabling future magnonic structures to emulate the established photonic and electronic components. As a proof-of-concept, we report magnon confinement in a lithographically defined all-on-chip YIG cavity created between two YIG/Permalloy bilayers. We take advantage of the modified magnetic properties of the covered/uncovered YIG film to define on-chip distinct regions with boundaries capable of confining magnons. We confirm this by measuring multiple spin-pumping voltage peaks in a 400 nm wide platinum strip placed along the center of the cavity. These peaks coincide with multiple spin-wave resonance modes calculated for a YIG slab with the corresponding geometry. The fabrication of micrometer-sized YIG cavities following this technique represents a new approach to control coherent magnons, while the spin-pumping voltage in a nanometer-sized Pt strip demonstrates to be a noninvasive local detector of the magnon resonance intensity.

Effect of oxygen vacancies on the electrical transport properties of conductive Y3Fe5O12 films at high temperature

Oxygen vacancies doping in oxide materials is a very common means to modulate the electrical transport properties. In this work, Y3Fe5O12 (YIG) films with abundant oxygen vacancies were grown on Gd3Ga5O12 substrates by solution spin coating and high vacuum annealing method, and the effect of oxygen vacancies on the electrical transport properties was systematically studied. It was found that a large amount of oxygen vacancies doping could convert the YIG film from a good room-temperature insulator to an electrical conductor. At high temperature and high vacuum, a large number of oxygen vacancies increased the disorder of the system, resulting in the appearance of a band-tail state, thus forming a constant range hopping conduction. While when the sample was exposed to air, the oxygen vacancies in the sample would gradually recombine and disappear, and the conduction mechanism transferred to drift mode.

Bragg resonances in sandwich magnonic crystals with non-identical periods

The paper reports on features of spin wave Bragg resonances in a sandwich structure consisted of two magnonic crystals, separated by a dielectric layer. Magnonic crystals are ferrite YIG films with periodic system of grooves with different periods on the surface. It is shown that in such a structure the symmetry of dispersion characteristics for direct and reflected waves with respect to the Bragg number is broken. As a result, the four resonances in the sandwich structure are observed in the vicinity of the first Bragg resonance of a single magnonic crystals. Resonances are formed at frequencies and wave numbers other than Bragg’s one for single magnonic crystals, and depends on a ratio of crystal periods.

The epitaxial iron-yttrium garnet films with homogeneous properties and narrow FMR line width

The growth of iron-yttrium garnet Y3Fe5O12 (YIG) films with of 1...15 μm thicknesses on single-crystal substrates of gallium-gadolinium garnet Gd3Ga5O12 (GGG) was carried out using the method of liquid phase epitaxy (LPE). The influence of the composition and mass of the charge, the temperature regimes, the rates of movement and the substrate rotation on the films parameters were studied. The layered structure caused by the heterogeneity of the chemical composition in the film thickness was determined and studied The dependence of the degree impurity of Pb2+ and Pt4+ ions in YIG films and their influence on the ferromagnetic resonance (FMR) line width ∆H on the films growth conditions was investigated. It’s shown that in order to obtain by the LPE method the series of defect-free films with low magnetic losses and reproducible parameters, it’s necessary to use melt-solutions of large mass (6...12 kg) and apply their additional mixing during the growth process.

Broadband ferromagnetic resonance of ultrathin yttrium iron garnet films by pulsed laser deposition: Effects of deposition parameters

In this study, we investigate the growth and characteristics of ultrathin ferrimagnetic yttrium iron garnet (YIG, Y3Fe5O12) films on a Gallium Gadolinium Garnet (GGG) substrate using the pulsed laser deposition technique (PLD). We aim to improve the magnetic quality of the films by varying the deposition parameters, specifically the laser energy and oxygen pressure. We conduct broadband ferromagnetic resonance (FMR) measurements to characterize the magnetic properties and Gilbert damping of the films. Our findings demonstrate that adjusting the deposition parameters systematically controls the saturation magnetization and Gilbert damping of YIG films. Our measurements show that in the absence of oxygen, the films exhibit higher-than-expected values of magnetization and Gilbert damping, suggesting that the films have a higher Fe concentration. Conversely, when introducing oxygen in the chamber, we observe a decrease in the magnetization and damping values, approaching those of bulk YIG films. Notably, we achieve a saturation magnetization of 0.185 T and an ultra-low Gilbert damping of 1.7 ×10−4 for films deposited under conditions of high laser energy and oxygen pressure. This is mainly due to a better Y:Fe ratio approaching the stoichiometric value of 0.6 as the oxygen pressure increased. Our findings provide valuable insights for preparing high-quality ferrimagnetic films suitable for various magnonics applications and spin Hall devices.

Praseodymium-dopant effect on bismuth-substituted yttrium iron garnet films on fused silica glass substrate at the 1310 and 1550-nm wavelengths

The optical and magneto-optic (MO) properties of the praseodymium (Pr)-dopant effect on bismuth-substituted yttrium iron garnet (Bi:YIG) films coated on fused silica glass substrates by using the metal-organic-decomposition (MOD) method with chemical solutions were investigated at the 1310 and 1550-nm wavelength regions. The maximum Faraday rotation angle of the Pr-codoped Bi:YIG (Pr,By:YIG) film was observed to be 0.09 and 0.046 deg/μm at the wavelengths of 1310 and 1550 nm, respectively, when the film was annealed at a temperature of 750 °C, while those of the plain Bi:YIG film were 0.059 and 0.039 deg/μm. More than 50% improvement in the Faraday rotation value of the Pr,Bi:YIG film was observed compared to that of the Bi:YIG film at the 1310 nm wavelength. The absorption coefficient of the Pr,Bi:YIG film was comparable to that of the Bi:YIG film. Therefore, the Pr,Bi:YIG film prepared with the MOD method is potentially useful for MO applications such as optical isolators and circulators.