Papers by Keyword: Yttrium Iron Garnet

Abstract: As a magneto-optical effect, the Faraday effect depends on the Verdet constant of the magnetic materials and enables integrated optical modulators and nonreciprocal photonic devices. Ferrimagnetic garnet, e.g. yttrium iron garnet (YIG) is the most studied material for terahertz (THz) Faraday effects. However, current works neglect the correlation between the Verdet constant and the electromagnetic (EM) parameters, which is vital for the design of high-performance THz non-reciprocal devices. Here, we investigate the mechanisms of the broadband THz rotations in undoped YIG and rare-earth doped YIG (La-doped) by polarization-sensitive THz time-domain spectroscopy. We observe a frequency-independent THz rotation angle (11/30 degree/mm) and related Verdet constant (70/170 degree/mm/T) for the YIG/ La-YIG, and further retrieve the EM parameters of YIG within the test range (0.3-2.5 THz). Based on these results, we establish a systematic methodology to describe the connections between the THz Faraday effects and corresponding materials. Our works provide critical foundation for the design and applications of the low-loss nonreciprocal THz devices in the future.

Abstract: Neodymium substituted yttrium iron garnet (YIG) nanoparticles with compositional variation of Nd_xY_3−xFe₅O₁₂ where x = 0.0, 0.2, 0.5 and 0.8 was prepared by mechanochemicals method using high energy milling (HEM). The characterization was done using X-rays diffractometer (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). It was found that the mechanical milling followed by sintering promotes the complete structural formation of the yttrium iron garnet (YIG) structure. The XRD patterns confirm the complete introduction of Nd³⁺ ion into the YIG with an addition of Nd doping concentration. nanocrystalline particles with high purity and sizes ranging from 0.12μm to 0.16μm were obtained. The magnetization value, M_s from all Nd-doped samples were obtained in the range between 34 to 37emu.g^-1. The magnetic coercivity (H_c) was achieved of 0.012kOe (12Oe) for the non-doped sample (YNd-0) and then increase with the addition of neodymium concentration. The increase in H_c for all the sample series can be attributed to an enhancement of the magnetocrystalline anisotropy with anisotropic Fe²⁺. The variation of the reflection loss (RL) versus frequency was observed in Nd doped YIG, Y_1-xNd_xFe₅O₁₂ with x = 0.0 – 0.8 in the frequency range of 7 –12 GHz. The optimum reflection loss (RL) was found to be 8.66(-dB) at 9.5GHz in Y_2.2Nd_0.8Fe₅O₁₂ (YNd-08) for x = 0.8.

Abstract: The optimization of magnetic uses of magnetic garnet type ferrites is largely known depending on their microstructure, synthesis process and chemical composition of the materials. This research investigates the effect of dopants substitution on microstructure and magnetic properties of Yttrium Iron Garnet (YIG). The oxide-mixture route was employed in synthesizing the YIG powders using Aluminium and Lanthanum as dopants with concentration of 0.5 prior to sintering at 1400 °C. The samples were characterized in several testing applications in order to study the structural, microstructural, magnetic properties and density effects toward the samples workability as ferromagnetic materials. Characterization of the samples were carried out by using Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), Impedance/Materials Analyzer and density measurement. The results showed that La-doped YIG shows an incredible achievement as a new ferromagnetic material, meanwhile with the substitution of Aluminum ion would increase the magnetic response of YIG.

Abstract: The cerium-substituted yttrium-iron garnet (Ce-YIG) in Ce_xY_3–xFe₅O₁₂ is considered as a promising material for applications in high frequency wireless communication technology. In this work, we reported the structural properties of Ce-YIG. This material was produced via conventional solid state reaction (CSSR) with various molar ratio of cerium (x = 0.0, 0.1, 0.5, 1.0, and 1.5, respectively). A heat treatment was at a temperature of 1420 °C for 6 h after pre-fired at 1100 °C for 6 h. Multiple phases were presented in Ce-YIG ceramics. It was found, at x=1.5, the substitution of Ce into YIG has reached the solid solution limit. It was seen that, the peaks were shifted to the lower angle and proportional to the amount of Ce added. Thus, it can be concluded that, the substitution of Ce into YIG was successfully at x=0.1,0.5, and 1.0 respectively before reaching the solid solution limit at x=1.5.

Abstract: Yttrium iron garnet (YIG) glass ceramic was successfully synthesized by aqueous aolution-melt method. The as-prepared base glass was heat treated at different temperature and investigated by XRD and VSM. The annealed glass at 580°C shows the formation of magnetite structure with saturation magnetization of 10.6A·m²/kg.And the annealed glass heat treating at 850°C for 6h, show the formation of garnet structure with saturation magnetization of 18.2A·m²/kg.

Abstract: Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material to be used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. This work presents the study of the ferrimagnetic composite, constituted by Y₃Fe₅O₁₂ (YIG) and Gd₃Fe₅O₁₂ (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screen-printing technique), in the microwave frequency range. The experiments with FRAs showed satisfactory results due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.

Abstract: Y3Fe5O12 (YIG) films were pulsed laser deposited onto the Gd3Ga5O12(111) substrates. Processing conditions were optimized to obtain films with a narrow ferromagnetic resonance (FMR) linewidth: 0.9 Oe in 1.22 μm thick YIG at 9 GHz. Due to sharp film-to-substrate interface YIG films remain strained hence possess unusually high lattice mismatch induced uniaxial anisotropy Hu = - 880 Oe. We fabricated and tested magnetostatic surface wave (MSSW) band pass hybrid-type filters with YIG film lain on transducers alumina board. MSSW filter with antennas areal size of 2 mm2 at 7.5 GHz shows insertion loss – 9 dB and a resonant 3 dB bandwidth as narrow as 12.5 MHz.

Abstract: Single phase YIG powders were synthesized successfully using Fe2O3 and Y2O3 as starting materials by solid state reaction, and YIG ceramics were prepared by pressureless sintering. The influence of synthesizing temperature and Fe2O3 content on the final production were studied The effect of Fe2O3 content on volume density and microstructure of the sintered YIG was also investigated. The results showed that single phase YIG powders were synthesized by solid state reaction at 1400°C for 3h. When Fe2O3 content was excessive 3 wt%, YIG ceramics with a density of 5.294g·cm-3 was fabricated by sintering at 1480°C for 2.5h.

Abstract: The effects of Bi-substitution on the complex impedance spectra of yttrium iron garnet (YIG) were studied in this paper. The polycrystalline yttrium iron garnet Y2BiFe5O12 (YIG: Bi) and Y3Fe5O12 (YIG) samples were prepared by solid-reaction method. The complex impedance spectra were measured in the frequency range from 1 KHz to 100MHz at several temperatures between 210oC and 500oC. The complex impedance sample shows that the YIG: Bi can be represented by double Cole-Cole semicircles, and the YIG can be represented by a single Cole semicircle. The physical structure of the specimen was visualized as comprising of small resistance grains separated by large resistance grain boundaries in accordance with the impedance spectra observations. The electrical processes in the sample were modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The temperature dependence of bulk resistance indicated an evidence of Arrhenius-type thermally activated process, showing a close to linear variation up to a temperature of 740 K.

Abstract: The low temperature sinterability and magnetic properties of Bi-substituted yttrium iron garnet (YIG) polycrystalline samples were studied in this paper. The results showed that Bi-substitution can lower garnet phase formation temperature from about 1200oC to 900oC and ceramic sintering temperature from over 1300oC to about 1050oC respectively. The Bi-substitution leads to a decrease in initial permeability and an increase in ferromagnetic resonance linewidth (ΔH) of sintered specimens. Saturation magnetization decreases and coercive force increases a few with an increase of Bi content. The mechanism of Bi-substitution on initial permeability and ΔH is discussed. The change in initial permeability of Bi-substituted specimens relative to unsubstituted YIG results from Bismuth volatilization and weakening of superexchange interaction. The lattice dilatation in Bi-substituted YIG gives cause for a decrease of saturation magnetization and an increase of coactivity force.