Lithium ferrites are discussed and compared with other spinel microwave ferrites and rare earth-iron garnets. Points of comparison are saturation magnetization, temperature performance, hysteresis loop properties, stress sensitivity, insertion loss, power handling capability, resonance linewidth, and cost. The main points of discussion deal with the relative effectiveness of lithium ferrites, nickel ferrites, magnesium ferrites, and garnets as elements employed in latching applications at frequencies in the S, C, X, and K/sub u/ bands. A section is devoted to the compositional modifications necessary for: 1) adjusting magnetization, spin-wave line width, coercive force, and magnetic anisotropy; 2) the minimization of stress sensitivity and dielectric loss; and 3) the improvement of microstructural characteristics.

Microwave Lithium Ferrites: An Overview

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

Yttrium Iron Garnet: Properties and Applications Review

Optical methods to measure electric parameters and transmit the information from high voltage circuits to ground potential are described and evaluated in the light of the specific requirements of high-voltage measurement applications. The history and physics of a variety of optoelectrical methods found suitable for electrical measurement applications are introduced. Existing optical devices for measuring alternating, direct, and impulse currents and voltages in high-voltage circuits are reviewed with emphasis on the operation and features of several selected methods. The use of these techniques in industrial systems, in research laboratory apparatus, and in reference standards laboratories is discussed.

Optical methods of electrical measurement at high voltage levels

The reaction of a mixture of iron acetylacetonate and rare-earth (Tm-Lu) acetate in 1,4-butanediol at 300°C yielded a novel phase of ReFeO3 having a hexagonal crystal system (a0 = 6.06, c0= 11.74 A) together with small amounts of Fe3O4and/or the garnet phase. The particle size of the product distributed in a narrow range and selected area electron diffraction from a particle having apparent polycrystalline outlines suggested that each particle was actually a single crystal grown from one nucleus. On calcination, the hexagonal phase irreversibly transformed into the perovskite phase at around 980°C. The use of ethylene glycol in place of 1,4-butanediol of the present procedure afforded Fe3O4, while hydrothermal reaction of the same starting materials yielded a mixture of Fe2O3and an amorphous rare-earth phase.

Glycothermal Reaction of Rare-Earth Acetate and Iron Acetylacetonate: Formation of Hexagonal ReFeO3

Microwave sintering (ms) process is applied to efficiently densify the (Bi 0.75 Ca 1.2 Y 1.05 )(V 0.6 Fe 4.4 )O 12 , Bi-CVG, materials, without inducing a deleterious effect on their microwave magnetic properties. A microwave sintering process can sinter the Bi-CVG materials to a density as high as 96.5%T. D., by firing the samples at 1030 °C (30 min). In contrast, it needs 1060 °C (6 h) to densify the materials to the same high density by a conventional sintering (cs) process. The ms-processed Bi-CVG materials possess pronouncedly smaller grain size (∼1.2 μm), which markedly hinders their low frequency magnetization process (in a few tens of MHz frequency regime), resulting in larger coercive field ( Hc ) and smaller initial permeability ( μ i ), as compared with the cs-processed large grain samples. But such a small grain characteristic insignificantly degrades the microwave magnetic properties, the resonance line width (Δ H ), of the Bi-CVG materials.

Microwave sintering of (Bi0.75Ca1.2Y1.05)(V0.6Fe4.4)O12 microwave magnetic materials

Recent advances in the study of microwave ferrites and garnets have resulted in a better understanding of the relationship between magnetic properties and the fundamental crystal structure. This article presents a review of the way in which the crystal structure of microwave garnets may be designed in order to realize the many different combinations of magnetic properties required by the designer of non-reciprocal microwave ferrites. The discussion relates to rare-earth and yttrium-containing garnets of the form Y3-αRαFe5O12 (R = rare earth Sm-Lu) and considers the effect of substitutions of Al, Ga, In, Mn, Ce, Ca and V on magnetization, gyromagnetic resonance, magnetic loss, high-power instability threshold and magnetostriction effects.

https://iopscience.iop.org/article/10.1088/0022-3727/3/3/204/pdf

A S Hudson

Papers

Molecular engineering in the design of microwave ferrimagnetic garnets