Hot-pressed polycrystalline yttrium iron garnet

A simple hot-pressing system is described which enables small volumes of polycrystalline yttrium iron garnet to be routinely produced. The products have high density, very low second phase content and a controlled grain size. Their magnetic properties compare very favourably with similar polycrystalline material produced by conventional sintering. Sample porosity may be varied in a controlled manner by simple changes in pressing conditions.     

Lead substitution in yttrium iron garnet

Polycrystalline and single crystal thin films of lead substituted Y₃Fe₅O₁₂ (Pb-YIG) have been prepared. The lattice parameter (a_o) has been measured as a function of composition and the relationship $\text{Δ}\text{a}{}_{\mathrm{o}}\text{= 0.040}\text{x}\text{A}\text{?}$ and 0.060x Å for polycrystalline and epitaxially grown films, respectively has been deduced (x is the number of lead atoms per formula unit). From the behaviour of polycrystalline Pb-YIG upon annealing we conclude that the thin films have a non-equilibrium composition. The hyperfine fields at the 57Fe nuclei measured by the Mössbauer effect are essentially the same as those of YIG. The Mössbauer spectra of the epitaxially grown films demonstrate that a growth-induced uniaxial magnetic anisotropy is present.     

Doped yttrium iron garnet for thermistor-bolometers

Yttrium Iron Garnet (YIG) crystals doped with divalent or tetravalent ions are shown to be promising as basic material for thermistor-bolometers. This is the first proposed device application of the $\text{electrical}$ properties of magnetic garnets. To illustrate the material performances, the static current-voltage characteristic and the voltage response versus current and frequency under a.c. laser irradiation are reported and discussed. The most attractive properties of doped YIG for thermistor-bolometer applications result to be the high responsivity, the speed of the response, and the high intrinsic absorbance in the ultraviolet, in the visible and in the near infrared.     

Synthesis of polycrystalline yttrium iron garnet and yttrium aluminium garnet from organic precursors

Polycrystalline Y₃Fe₅O₁₂ (YIG) and Y₃Al₅O₁₂ (YAG) garnets have been prepared by the organic solution technique using a novel organic precursor. The thermal decomposition of the precursor and subsequent formation of the garnet phases was studied by thermal analysis, X-ray diffraction and Fourier transform infra red spectroscopy (FTIR) including diffuse reflectance FTIR (DRIFT). The precursor of YIG decomposes to give the garnet phase as the main component at 800 °C. YFeO₃ and Fe₂O₃ are also present, and react to give YIG at higher temperatures. Single-phase YAG can be obtained from its precursor at 1100 °C. The reaction proceeds via a hexagonal YAlO₃ intermediate which is formed at 850 °C.     

Open die hot pressing of yttrium iron garnet

A relatively simple and more economical process of open die hot pressing has been employed in preparing high density yttrium iron garnet samples of fine grain size (～ 1–2 μM). The samples have been investigated for the microstructure dependent spinwave line-width (ΔH_k) and FMR line-width (ΔH). The values of ΔH_k and ΔH are in fair agreement with the samples having the same grain size but prepared by the conventional hot pressing using refractory dies.     

Reaction between lead zirconate titanate and yttrium iron garnet

High-temperature sintering of lead zirconate titanate (PZT) + yttrium iron garnet mixtures is accompanied by the formation of cubic yttria-stabilized zirconia. Quantitative phase analysis indicates that PZT loses at least 90% of the ZrO₂. This leads to appreciable changes in the composition of the constituent phases and has an adverse effect on the ME performance of the composite     

Broadened low-field modes in thick yttrium iron garnet epilayers

Damped surface modes in thick YIG epilayers which appear at fields below the Damon-Eshbach limit in microwave spectra with the dc magnetic field parallel to the surface, have been investigated. The introduction of a surface anisotropy term in the boundary conditions of the propagation equations qualitatively accounts for these low-field modes.     

Observation of a cubical-like microstructure of strontium iron garnet and yttrium iron garnet prepared via sol-gel technique

This is our initial response towards preparation of nano-inductors garnet for high operating frequencies strontium iron garnet (Sr3Fe5O12) denoted as SrIG and yttrium iron garnet (Y3Fe5O12) denoted as YIG. The garnet nano crystals were prepared by novel sol-gel technique. The phase and crystal structure of the prepared samples were identified by using X-ray diffraction analysis. SEM images were done to reveal the surface morphology of the samples. Raman spectra was taken for yttrium iron garnet (Y3Fe5O12). The magnetic properties of the samples namely initial permeability (micro), relative loss factor (RLF) and quality factor (Q-Factor) were done by using LCR meter. From the XRD profile, both of the Y3Fe5O12 and Sr3Fe5O12 samples showed single phase garnet and crystallization had completely occurred at 900 degrees C for the SrIG and 950 degrees C for the YIG samples. The YIG sample showed extremely low RLF value (0.0082) and high density 4.623 g/cm3. Interesting however is the high Q factor (20-60) shown by the Sr3Fe5O12 sample from 20-100 MHz. This high performance magnetic property is attributed to the homogenous and cubical-like microstructure. The YIG particles were used as magnetic feeder for EM transmitter. It was observed that YIG magnetic feeder with the EM transmitter gave 39% higher magnetic field than without YIG magnetic feeder.     

Synthesis of yttrium iron garnet precursor particles by homogeneous precipitation

Yttrium iron garnet (YIG) precursor particles were obtained by homogeneous precipitation in a nitrate salt solution by a reaction involving the thermal decomposition of urea. Chemical analysis indicated that solid phases were initially precipitated with sequential iron ion content. The precipitate formed was an amorphous mixed iron oxide phase. The complex composition and the thermal decomposition of the precipitate were studied by thermogravimetry-differential thermal analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform-infrared spectroscopy. Precipitate morphology was observed by SEM and TEM. Fine-grained single-phase yttrium iron garnet (YIG:Y₃Fe₅O₁₂) powders were obtained by calcination of the precipitate at 1200 °C. YFeO₃ intermediate compound was formed at 600 °C prior to the final crystallization of YIG.     

Electromagnetic excitation of ultrasonic oscillations by yttrium iron garnet films on gallium gadolinium garnet substrates

We have studied the phenomenon of contactless excitation of ultrasonic oscillations by thin yttrium iron garnet (YIG) films on gallium gadolinium garnet (GGG) substrates upon application of the superposition of a constant magnetic bias field and alternating magnetic field. Dimensional resonance effects that cannot be explained in the framework of existing theoretical notions have been discovered, in particular, in dependences of the amplitude of excited longitudinal oscillations on the YIG film thickness, frequency of ultrasound, and degree of homogeneity and strength of the magnetic bias field. It is suggested that the observed phenomenon is caused by resonant participation of the intrinsic oscillations of domain walls in the excitation of ultrasound.     

Selective growth of yttrium iron garnet and yttrium ferrite by combinatorial pulsed-laser ablation of common precursors

In this paper, we demonstrate the capability of growing two alternative complex oxides with different stoichiometries and crystal structures, by choosing the appropriate substrate and adjusting the target ablation ratio, and tuning their composition and properties by combinatorial pulsed-laser ablation of their precursors. In particular, we successfully grew epitaxial crystalline yttrium iron garnet (Y₃Fe₅O₁₂) on yttrium aluminium garnet (Y₃Al₅O₁₂) substrates and polycrystalline yttrium ferrite (YFeO₃) on sapphire (α-Al₂O₃) substrates by co-ablation of yttrium oxide and iron oxide targets.     

Tunable magnetostatic waves bandpass filters with scandium doped yttrium iron garnet films

This paper reports results of theoretical and experimental studies of microwave bandpass tuned filters based on magnetostatic surface wave (MSSW) propagation in yttrium iron garnet (YIG) films. Filter transmission and input impedance characteristics for saturation magnetization 139 kAm^–1 of YIG films and 32 kAm^–1 of scandium-doped YIG films have been calculated and measured experimentally. Structures of a planar, multilayer metal-dielectric-YIG geometry are used to model the filters. Parameters of the structures have been optimized with the help of a computer. Scandium-doped YIG films of thickness near 100 m and saturation magnetization 32 kAm^–1 have been found potentially useful in the manufacture of tunable bandpass filters.     

Dielectric properties and electrical conduction in yttrium iron garnet (YIG)

The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y₃Fe₅O₁₂) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.     

Flux-gate magnetic field sensor based on yttrium iron garnet films for magnetocardiography investigations

Technical Physics Letters - A new type of f lux-gate vector magnetometer based on epitaxial yttrium iron garnet films has been developed and constructed for magnetocardiography (MCG)...     

Stochastic generation accompanying parametric excitation of spin waves in yttrium iron garnet films

We report the results of experimental investigations of chaotic self-modulation of the envelope of surface spin waves as a result of first-order spin-wave parametric instability. The experimental apparatus consisted of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. Tekh. Fiz. 24, 66–72 (April 12, 1998)     

Densification and microstructure development in the reaction sintering process of yttrium iron garnet

Factors affecting the densification and microstructure development in the reaction sintering process (RSP) of yttrium iron garnet were investigated. Three different powder mixtures were used: Fe₂O₃/Y₂O₃, Fe₂O₃/YFeO₃ (1100 ° C calcined), and Fe₂O₃/YFeO₃ (1200 ° C calcined). The conventionally prepared garnet powder was also adopted as a reference material. It was found that the RSP using Fe₂O₃-YFeO₃ systems has a beneficial effect on densification from the dilatation occurring along with the reaction of garnet formation. On the other hand, it has a detrimental effect due to the local contraction induced by the reaction in the Fe₂O₃-Y₂O₃ system. The densification rate and ultimate density achievable are also affected by the YFeO₃ powder adopted in RSP. A high grain-growth rate was obtained for garnet when the 1200 ° C calcined YFeO₃ powder was used. This leads to a high densification rate at low temperature. However, the densification ability deteriorates at temperatures above 1425 ° C due to the trap of pores in the fast-grown grains. Conversely, the grain-growth rate in RSP with 1100 ° C-calcined YFeO₃ was moderate, and although it gives a slower densification rate at low temperature, the ultimate density can be raised to 99% theoretical density at 1450 ° C.     

Electromagnetic coupling between two parallel layers of yttrium iron garnet for microwave device applications

AnXband microwave filter consisting of two microwave cavities attached and orthogonal to each other with a YIG-GGG-YIG sample in a sandwich configuration has been designed and tested. Normally the two cavities do not couple electromagnetically to each other, but do couple through the sandwich configuration. The sandwich configuration is placed in between the two cavities so that there is one YIG film in each cavity. The amount of coupling can be varied by: (1) the magnitude of the static field,|overrightarrow{H}|, and (2) the angle betweenoverrightarrow{H}and the film surface. The parallel layering of the two YIG films is essential in the improved performance of the microwave filter.     

The magnetic and dielectric properties of microwave sintered yttrium iron garnet (YIG)

Yttrium iron garnet (YIG) material is widely used in microwave devices. Experiments show that microwave sintering (MS) treated YIG materials possess excellent properties with a saturation magnetization of 14.60 emu/g and coercive force 34.82 Oe. In the frequency range of 1 MHz–1.8 GHz, the relative dielectric constant is from 6.5 to 7.0, the line-width is 105 Oe, dielectric loss less than 0.09 and magnetic loss less than 0.7. Furthermore, the sintering time and temperature were significantly reduced from 20 h and 1300 °C for the conventional sintering (CS) process to 2 h and 900 °C for MS technique, respectively.