Bi-substituted Yttrium Iron Garnet Research Articles

Mechanism of the impact of Ca–Ge co-substitution on the FMR linewidth in BiV-YIG ferrites

Yttrium Iron Garnet (YIG) ferrites, characterized by their superior magnetic and dielectric attributes, are instrumental in advancing the development of microwave devices, particularly in enhancing high-frequency performance, integration, and miniaturization. This paper synthesizes YIG ferrite materials with the composition Bi0.6Y1.4-xCa1+xFe4.5-xV0.5GexO12 (x = 0.10 to 0.50, incrementing by 0.10) through the solid-state sintering method. It delves deeply into the mechanism by which Ca2+-Ge4+ ions substitution regulates the magnetic properties of BiV-YIG. The microstructural and magnetic properties of the samples were systematically tested and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), vibrating sample magnetometry (VSM), and TE106 perturbation method. At a substitution content of x = 0.50, the substitution of Ge4+ ions for the Fe3+ ions at the d-site transforms the material from ferrimagnetic to paramagnetic, and the saturation magnetization of the sample drops to 132.74 G. By calculating the ferromagnetic resonance (FMR) linewidth using the law of approach to saturation, the study elucidates the negative impact of low saturation magnetization on FMR linewidth. The mechanisms proposed in this paper provide theoretical and experimental bases for reducing the FMR linewidth of high dielectric constant Bi-substituted YIG, paving the way for developing high-dielectric, low-loss YIG ferrite materials for microwave devices.

Underlying mechanism of the driving force for generating spin currents thermally in a ferrimagnetic insulator due to a temperature gradient

We previously proposed the idea that the effective thermal-energy transfer from the phonon system to the spin system in liquid phase epitaxial (LPE) films of Bi-substituted yttrium iron garnet (Bi:YIG), a ferrimagnetic insulator, takes place through enhanced spin-orbit coupling (SOC) with local 3d-electron spins in Fe3+ ions, and that the spin-thermoelectric (STE) generation in a paramagnetic platinum (Pt) layer is raised by increased spin pumping to the Pt layer from the Bi:YIG film. However, we could not specifically relate the underlying mechanism to the driving force for the generation of spin currents due to nonequilibrium dynamics of magnons driven by the temperature gradient ∇T in a magnetic insulator. In this paper, we discuss the origin of the driving force for generating spin currents, which are increased through enhanced SOC in LPE yttrium iron garnet films.

Preparation and orientation mechanism analysis of (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> magneto-optical single crystal film with out-of-plane orientation

Liquid-phase epitaxy (LPE) is one of the best techniques for the preparation of single crystal garnet films. However, the specific Faraday rotation angle of Yttrium iron garnet (YIG) is small, and its easy magnetization axis is parallel to the film surface. The YIG requires a large external saturation field, which cannot meet the development needs of magneto-optical devices. It is found that Bi-substituted YIG(Bi:YIG) film has a larger specific Faraday angle. By adjusting the easy magnetization axis of Bi: YIG perpendicular to the film surface, the saturation magnetization of Bi: YIG can be reduced, so that it can work under a small external magnetic field. This meets the development needs of miniaturization and energy saving of magneto-optical device. The saturation magnetization of garnet film can be effectively reduced by substituting Ga<sup>3+</sup> for YIG crystal, mainly for Fe<sup>3+</sup> at the 24d position of its tetrahedron. And the lattice constants of Gd<sub>3</sub>Ga<sub>5</sub>O<sub>12</sub> (GGG) and YIG are 1.2383 nm and 1.2376 nm, respectively. However, the radius of Bi<sup>3+</sup> (10.8 nm) is larger than that of Y<sup>3+</sup> (9.0 nm), the lattice mismatch of garnet film increases with the incorporation of Bi<sup>3+</sup>. In order to neutralize the lattice expansion caused by Bi<sup>3+</sup>, Tm<sup>3+</sup> (8.69 nm) with a radius smaller than that of Y<sup>3+</sup> (9.0 nm) is selected. Based on the theoretical analysis of the magnetocrystalline anisotropy of garnet film, (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> mono-crystalline films with different growth temperatures and different thickness values are grown by LPE on GGG (111) substrates. The experimental results show that when the thickness of epitaxial film is greater than 1 μm, the influence of shape anisotropy on magnetocrystalline anisotropy can be ignored. With the increase of growth temperature, the substitution number of Bi<sup>3+</sup> ions decreases gradually, the lattice constant of epitaxial film decreases gradually, and the lattice mismatch first decreases and then increases. Then, the state of compressive stress gradually changes into that of tensile stress. Compared with growth-induced anisotropy, the stress-induced anisotropy is dominant in the change of magnetocrystalline anisotropy. The Verdet constant of (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> film is 11.8 × 10<sup>4</sup> rad/Tm@1064 nm. The results show that the prepared (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> mono-crystalline films have great development potential in magneto-optical devices.

Magnetic behavior and characterization of La, Pr, and Bi substituted yttrium iron garnet

In this study, the structural and magnetic properties of rare-earth-doped garnets, RxY3-xIG (R = La, Pr, and Bi), prepared by the solid-state route were evaluated. Ce0.25Pr0.25Bi0.15Y2.35Fe5O12, Ce0.25Pr0.25Bi0.2Y2.3Fe5O12, Ce0.15Bi0.15La0.1Y2.6Fe5O12, Ce0.15Bi0.15La0.2Y2.5Fe5O12, Ce0.15Bi0.15Dy0.2Y2.5Fe5O12 and Ce0.25Pr0.5Bi0.15Y2.1Fe5O12 were prepared and compared with each other. The structural and microstructural studies were carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The magnetic behavior was identified by a vibrating sample magnetometer (VSM). The XRD results revealed that the synthesized powders have a relatively high purity. The XPS data confirmed the minute amounts of impurities. A single garnet phase with a relatively high purity was formed in all the samples. The crystallite size was estimated using high resolution-TEM images with an average size of 20 nm. The samples with Bi3+cation show the maximum value of Ms in comparison with the samples containing La3+, Dy3+, and Pr3+ at about 35.26 emu/g due to the enhancement of the super-exchange interaction and the variation of the bond length and bond angle. Instead, in the samples with La3+, Ms decreases with the minimum amount for xLa = 0.2. As the La increased from 0.1up to 0.2, the Ms decreased from 31.03 to 28.60 emu/g. By increasing the Pr3+ content from 0.25 to 0.5, Ms increased from 29.31 to 33.16 emu/g as expected based on Neelʼs theory. In addition, by comparing the samples Ce0.15Bi0.15La0.2Y2.5Fe5O12 and Ce0.15Bi0.15Dy0.2Y2.5Fe5O12, it was found that in a fixed amount of dopants the Ms of the sample containing Dy is 31.14 emu/g, which is 2.08 more than that of the sample containing La. Generally, by comparing the samples with one another, it can be figured out that the sample with the chemical composition of Ce0.25Bi0.2Pr0.25Y2.3Fe5O12 shows the maximum value of saturation magnetization.

The role of Dy incorporation in the magnetic behavior and structural characterization of synthetic Ce, Bi-substituted yttrium iron garnet

In this Study, the effects of substitution of Y3+ by Dy3+ ions on the crystal structure and magnetic properties for Y2.8-xDyxCe0.10Bi0.10Fe5O12 (x = 0.0, 0.2, 0.4, 0.6) and pure yttrium iron garnet (YIG) produced by conventional method have been investigated. The Fe2O3, Y2O3, CeO2 and Dy2O3 powders were mixed in stoichiometric ratio and annealed at different temperatures from 1000 to 1420 °C in air atmosphere. At the final stage, Bi2O3 was aggraded in the YIG and annealed in 1000 °C in an air atmosphere. The phase structure, morphology and magnetic properties were investigated using Raman Spectroscopy (RS), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM), respectively. The X-ray diffraction data showed a nearly pure and single-phase of doped garnet with small amounts of CeO2 secondary phase. The RS result reveals the characteristic peak of the YIG structure. The XPS analysis indicates that bismuth, dysprosium, yttrium and iron ions exist in their corresponding “+3” valence states whereas cerium finds in “+3” and “+4”. The saturation magnetization augments from 33.47 emu/g for pure YIG to 35.15 emu/g for xDy = 0.2 due to the small increase in d-p wave function overlap between the octahedral Fe3+ ion and intervening oxygen ion. The coercivity values decrease from 20.16 Oe for pure YIG to 17.78 Oe for xDy = 0.6. The improved magnetic properties promote the doped garnets to microwave absorption and sensing applications.

Advanced aperture cantilevers made by focused ion beam for both magnetic domain structure and morphology investigation in high resolution magneto optical microscopy

Magneto-optical microscopy is a well-known and widely used method of magnetic domain structure investigation. Spatial resolution is limited by diffraction limit of the light and practically not exceed 0.5μm. Possibility to overcome diffraction limit by combination of magneto-optical microscopy and magnetic-force microscopy was showed earlier [1]. Aperture cantilever was used to light up the sample in near-field mode. In this paper, authors review most popular technology for aperture cantilever production with its advantages and disadvantages. Authors propose new technology based on focused ion beam treatment for creation aperture cantilevers with advanced parameters such as small aperture size and light throughput. Bi-substituted yttrium iron garnet (Bi: YIG) thin films with high magneto-optical activity and different period of domain structure were used as test objects. High resolution images of both morphology and domain structure obtained with new advanced aperture cantilevers are shown.

Miniaturized magneto-optical imaging sensor for crack and micro-crack detection

A highly-sensitive magneto-optical Faraday sensor was miniaturized, including Bi-substituted yttrium iron garnet (Bi: YIG) thin films. The magnetic field over the surface of the cracked steel was measured by using this sensor. The results demonstrated that this sensor could illustrate the micro-cracks on the surface and subsurface of the sample and was a proper candidate for Magnetic Flux Leakage method. In addition, the possibility of the crack and micro-crack detection was evaluated by utilizing a magneto-optical miniaturized sensor. The experimental setup encompassed miniaturized optical setup, Bi: YIG thin films, and some samples with different cracks and micro-cracks. The results of the present study revealed that the sensor can focus on the sample up to 1 μm and its output represented good sensitivity to the crack parameters. This technique can be proficient to high resolution and miniaturized magneto-optical sensor since it can find the cracks and micro-cracks on the sample surface for application in magnetic flux leakage test industry.

Magneto-optical images of submicron-size Bi-substituted YIG patterns prepared by electron-beam irradiated metal-organic decomposition

We investigated the magneto-optical properties of submicron-size epitaxial Bi-substituted yttrium-iron garnet (Bi:YIG) patterns fabricated by an electron-beam irradiated metal-organic decomposition (EB-MOD) method. The advantage of this method is that no dry etching process is required. The Bi:YIG pattern showed the clear magneto-optical Kerr effect (MOKE) hysteresis loop, and it was in good agreement with the magnetization curve of the Bi:YIG patterns. The MOKE image measurements revealed that the Bi:YIG pattern with a width of ∼0.71 μm prepared by the EB-MOD showed proper contrast changing behavior depending on magnetic fields, and it can maintain its MO property even in submicron-size.

Proposal for a microwave photon to optical photon converter based on traveling magnons in thin magnetic films

Abstract In this work, we propose a concept of a microwave to optical photon converter for applications in Quantum Information (QI) that is based on travelling magnons in a thin magnetic film. The converter employs an epitaxially grown Bi-substituted yttrium iron garnet (Bi-YIG) film as the medium for propagation of travelling magnons (spin waves). The conversion is achieved through coupling of magnons to guided optical modes of the film. We evaluate the conversion efficiency for this device theoretically. Our prediction is that it will be larger by at least four orders of magnitude than experimentally obtained in a similar process exploiting a uniform magnetization precession mode in a YIG sphere. By creating an optical resonator of a large length from the film (such that the traveling magnon decays before forming a standing wave over the resonator length) one will be able to further increase the efficiency by several orders of magnitude, potentially reaching a value similar to achieved with opto-mechanical resonators. An important advantage of the suggested concept of the QI devices based on travelling spin waves is a perfectly planar geometry compatible with the optical lithography process and a possibility of implementing the device as a hybrid opto-microwave chip.

Enhanced magneto-optical Faraday effect in 2D magnetoplasmonic structures caused by orthogonal plasmonic oscillations

In recent research we present results of transmission and Faraday angle rotation theoretical simulations and experimental study in magnetoplasmonic 2D structures based on perforated with subwavelength holes gold film on top of a smooth Bi-substituted yttrium iron garnet (BiYIG). It was shown that in the case of normal incident light it is possible to enhance Faraday angle rotation mainly through excitation of orthogonal plasmonic oscillations.

Bi-Directional Faraday Rotation Selective Enhancement on Embedded Nano-Gratings

The magneto-optic rotation enhanced by plamonic resonance brought a new method in the research of magnetoplasmon and magneto-optical devices. To further the availability of this method, the Faraday effect on embedded nano-gratings with Bi-substituted yttrium iron garnet substrate is investigated here to achieve bi-directional rotation enhancement selectively. The surface of the simulation structure is designed as 1-D gratings to excite extraordinary optical transmission, and the transmitted light is rotated in the magneto-optic (MO) material. It is found that the characteristic of the bi-directional Faraday rotation enhancement can be greatly influenced by the embedding depth of the metal strips in the MO material. According to this, without changing the applied magnetic field or turning over the MO material, the selectively enhanced Faraday rotation is produced along two opposite directions. Moreover, by optimizing the thickness of metal, a great improvement of figure of merit is obtained. Finally, in the same wavelength regime, the properties of the structure are contrasted when the metal is set to be gold or silver, respectively. This letter provides a useful thought in magnetoplasmon studies, and can be used to fabricate many magneto-optical devices.

The Effect of Faraday Rotation Enhancement in Nanolayered Structures of Bi - Substituted Iron Garnets

The effect of considerable enhancement of Faraday rotation (FR) and figure of merit (Q) in Bi, Gd, Al-substituted iron garnets plus Bi2O3 (Bi, Gd, Al: YIG / Bi2O3) nanocomposite films on Gd3Ga5O12 (GGG) substrates was found. It reached threefold enhancement of the FR and twofold of the Q one. These films were produced by reactive ion beam sputtering of appropriate targets and following separate annealing. In addition it was determined that in double layer Bi-substituted yttrium iron garnet (Bi: YIG) nanostructures on GGG substrates the upper layer (0.5 – 3.0 nm) considerably affects the magneto-optical properties of the “thick” (8.0 – 10.0 nm) bottom layer. The possible reasons of these effects are discussed.

Evaluation of Nonlinear Effect in High Power Spin Pumping in Polycrystalline Bi-Substituted Yttrium Iron Garnet (Bi:YIG)/Pt Bilayer Structure

We have demonstrated a quantitative evaluation of spin pumping at uniform excitation in linear and nonlinear regimes of microwave absorption in a polycrystalline Bi-substituted yttrium iron garnet (Bi:YIG)/Pt bilayer structure. The evaluation is performed based on a ratio of magnitude of pumped spin currents to amplitude of uniform precession which are estimated from inverse spin Hall effect voltage and microwave absorption intensity at various incident powers. The ratio shows additional contribution to spin pumping by spin waves generated from uniform precession via nonlinear coupling between them. We have also clarified the additional contribution by the generated spin waves at various frequencies based on the ratio.

Spin Pumping without Three-Magnon Splitting in Polycrystalline Bi1Y2Fe5O12/Pt Bilayer Structure

Spin pumping at various precession frequencies has been investigated in a polycrystalline Bi-substituted yttrium iron garnet (Bi:YIG)/Pt bilayer structure by means of inverse spin Hall effect (ISHE) with comparison to a single crystal La-substituted yttrium iron garnet (La:YIG)/Pt bilayer structure which shows three-magnon splitting. As precession frequency decreases, the magnitude of pumped spin currents in the polycrystalline sample continuously increases to high magnitude comparable to the highest magnitude in the single crystal sample while that in the single crystal sample decreases below a threshold frequency of three-magnon splitting. By comparing ISHE voltage with microwave absorption intensity in the polycrystalline sample, we verify that the large magnitude of the pumped spin currents is maintained at low frequencies through the suppression of three-magnon splitting.

Magnetic and magnetodielectric properties of Bi-substituted yttrium iron garnet ceramics

Effects of Bi substitution upon magnetic and magnetodielectric properties of Y3Fe5O12 ceramics were investigated. It was found that the saturation magnetization decreases and the magnetic ordering temperature increases as the amount of Bi increases. The contribution of intrinsic and extrinsic effects to magnetodielectric effects decreases with increase of Bi, which results in the decrease of magnetodielectric coefficient of Y3−xBixFe5O12 ceramics.

Adjustable Faraday rotation by using engineered one-dimensional magneto photonic crystals

We investigated the adjustability and enhancement of magneto-optical Faraday rotation in one-dimensional magneto photonic crystal. The Faraday rotation can be adjusted through optical contrast ratio engineering in the resonator structure via equivalent layers theory. Also, simultaneous enhancement of the transmission magnitude and Faraday rotation of the structure can be obtained by optimizing the optical contrast ratio-magnetic defect layer thickness product. In a special design of magneto photonic crystal which consists of SiO 2 and Ta 2O 5 as the basic element of the resonator and Bi substituted yttrium iron garnet as the defect magnetic layer, by changing the optical contrast ratio from 1.43 to 1.09, the Faraday rotation can be adjusted from −3.35 to −0.74 deg in 65 nm wide range of wavelength. Finally, in the case which the optical contrast ratio optimized at 1.22 and the thickness of magnetic defect layer changed to one quarter of design wavelength, dramatic simultaneous enhancement of Faraday rotation and transmission magnitude can be obtained succesfully (the Faraday rotation and transmittance have their maximum value, −11.77 deg, and 99.67%).

Magneto-optical properties of Bi-substituted yttrium iron garnet films by metal-organic decomposition method

Recently, Bi-substituted yttrium iron garnet has been used as an indicator that visualizes magnetic flux distribution utilizing magneto-optical (MO) effect. In order to improve the sensitivity and the spatial resolution in the MO imaging, higher Bi substitution and thinness less than 1μm are required. For the purpose, Y3−xBixFe5O12 (Bi:YIG) films with high Bi substitution of x=1.0 – 2.5 were obtained on Gd3Ga5O12 (111) substrates by metal-organic decomposition method in this study. Magneto-optical spectra were measured for all samples, and Faraday rotation was found to be 1.55 × 105 degree/cm at wavelength of 524 nm for x = 2.5 film. For the spatial resolution, magnetic recording marks with a length of 0.6 μm was clearly resolved by using 200 nm-thick Bi:YIG with x = 2.5.

Manipulation of Faraday rotation in Bi-substituted yttrium-iron garnet film using electromagnetic interaction between Au nanoparticles in two-dimensional array

The Faraday rotation in Bi-substituted yttrium-iron garnet thin films, in which an artificially fabricated Au nanoparticle array is embedded, is studied as a function of lattice spacing compared with the extinction spectra. With decreasing lattice spacing in the Au array, the wavelengths corresponding to the enhanced Faraday rotation and the extinction peak showed blueshifts in the same manner. This indicates that Faraday rotation can be manipulated by means of the wavelength shift of localized surface plasmon resonance that originates from the change in electromagnetic interaction between Au nanoparticles.

Molten-salt synthesis and characterization of Bi-substituted yttrium garnet nanoparticles

Bi-substituted yttrium iron garnet (Bi-YIG, Bi 1.8Y 1.2Fe 5O 12) nanoparticles were successfully synthesized by molten-salt method in NaCl–KCl flux at 650 °C. Subsequently, X-ray powder diffraction, scanning electron microscopy, dynamic light scattering and vibrating sample magnetometer tests were used to characterize the phase, morphology, size distribution and magnetic properties of the as-prepared Bi-YIG nanoparticles, respectively. Moreover, the transparence and Faraday rotation of the PMMA slices filled with Bi-YIG nanoparticles were investigated by ultraviolet–visible spectrophotometer and Faraday rotation meter, respectively.

Large enhancement of Faraday rotation by localized surface plasmon resonance in Au nanoparticles embedded in Bi:YIG film

A large enhancement of the Faraday rotation, which is associated with localized surface plasmon resonance (LSPR), was obtained in a sample with Au nanoparticles embedded in a Bi-substituted yttrium iron garnet (Bi:YIG) film. On a quartz substrate, Au nanoparticles were formed by heating an Au thin film, and a Bi:YIG film was then deposited on them. A sample containing the Au nanoparticles produced by 1000 °C heating showed a resonant attenuation with narrower bandwidth in the transmission spectrum than nanoparticles of other samples formed by low-temperature heating. The sharp resonant Faraday rotation angle was 4.4 times larger than the estimated intrinsic Bi:YIG film at the LSPR wavelength; the angular difference was 0.14°. A discrepancy in the bandwidth between the transmission attenuation and the resonant Faraday rotation is discussed.