Aluminum Substituted Yttrium Iron Garnet Research Articles

Influence of aluminum substitution on microstructural, electrical, dielectric, and electromagnetic properties of sol-gel synthesized yttrium iron garnet (YIG)

Aluminum-substituted Yttrium iron garnet (Al-YIG) (Y3AlxFe5−xO12; x = 0.4, 0.8, 1.2, 1.6, and 2.0), samples were synthesized via an auto-combustion sol-gel technique. The obtained powder was heated at 950 °C, pressed into pellets, and sintered at 1200 °C. The sample microstructures were studied using field emission scanning electron microscopy (FESEM). The average grain size decreased from 0.46 μm at x = 0.4 to a minimum value of 0.33 μm at x = 2.0. The elemental composition of the samples was studied by energy dispersive x-ray (EDX), while the bulk density was measured by the Archimedes principle. Electrical and dielectric measurements were carried out using an Agilent impedance analyzer. Generally, the sample resistivity decreased with Al concentration. At 1 MHz frequency, the sample x = 0.4 has the highest resistivity of 2.19 × 105 Ωm, which decreases down to its minimum value of 1.75 × 104 Ωm at x = 2.0. The dielectric constant for all the samples decreased with frequency. For the sample x = 0.4, the ε′r decreased from 49.03 at 40 Hz to 8.08 at 1 MHz. The dielectric loss tangent, tan δ, decreased with increasing frequency, while it increased with Al substitution. Permeability values were calculated from permittivity data. The real permeability decreased from 1263.12 at x = 0.4 to 6.96 at x = 1.2 and decreased down to 11.74 at x = 2.0. The high dielectric constant, low resistivity, and low loss values of the samples indicate their suitability for miniaturization of radio frequency devices, antenna, and filter resonators.

Structural and Magnetic Studies of Aluminum Substituted YIG Nanoparticles Prepared by a Sol-Gel Route

The aluminum substituted Yttrium Iron Garnet nanoparticles were synthesized by sol-gel route followed by annealing at 700°C and 900°C for 3 and 2 h respectively. The XRD patterns of all the samples confirmed the single-phase and well-defined garnet structure at 900°C. The average crystallite size of the samples calculated using Scherrer formula was found in the range of 56–69 nm. The lattice parameter and d-spacing were found to decrease with increasing aluminum content due to the smaller ionic size of the Al3+ cation. FTIR spectra confirmed the garnet phase formation and showed stretching mode of YIG tetrahedron in the range of 552–657 cm−1. It was observed from hysteresis loops that the saturation magnetization (Ms) values decreased from 20.69 emu/g to 3.09 emu/g with increasing aluminum content. Electron spin resonance (ESR) study showed the broadening of a peak to peak linewidth with increasing aluminum content. The minimum linewidth of 110 gauss was observed for YIG sample.

Microwave-hydrothermal synthesis of Y3Fe3.35Al1.65O12 nanoparticles for magneto-hyperthermia application

Crystalline aluminum substituted yttrium iron garnet nanoparticles Y3Fe3.35Al1.65O12 (YIG) was synthesized by hydrothermal microwave synthesis at 140 °C with soaking times ranging from 15 to 60 min. X-ray diffraction confirmed the single-phase YIG nanoparticles excluding the presence of any other phases in the reaction products. The Raman spectra revealed that the largest soaking time provides greater energy crystallization causing changes of lattice vibration and a certain degree of disorder in the crystal lattice. Field emission gun-scanning electron microscopy and high resolution transmission electronic microscopic revealed a homogeneous size distribution of nanometric YIG powders with agglomerated particles. Magnetic measurements were achieved by using a vibrating-sample magnetometer unit. YIG nanoparticles have great potential in magneto-hyperthermia application once in vivo applications magnetic induction heating ferromagnetic compounds generate heat in AC magnetic fields.

Colorization of Magnetic Hologram Images With Optical Space Division Method

We have developed magneto-optic spatial light modulators (MOSLMs) with submicrometer-size magnetic pixels for wide-viewing-angle holographic displays (3-D-MOSLM) that are driven by the thermomagnetic recording. The holographic images were reconstructed by the magnetic hologram pattern on the MOSLM. In this paper, we have studied colorization of reconstruction images of the MOSLMs using optical space division method. This method used some 3-D-MOSLMs to represent intermediate colors. The magnetic films were polycrystalline bismuth, dysprosium, and aluminum substituted yttrium iron garnet (BiDyYFeAlG) films with perpendicular magnetization. The thickness of BiDyYFeAlG films was designed for each wavelength. The MOSLM represented (3-D) images with intermediate colors that were synthesized 3-D images with red and green colors. In addition, tones of intermediate colors were represented by controlling intensity of each reference light. These results demonstrated that 3-D-MOSLMs have promise for full-colorized holographic 3-D displays.

Morphology and Magnetic Characterisation of Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

Aluminum substituted yttrium iron garnet nano particles with compositional variation of Y(3.0-x) A1(x)Fe5O12, where x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 were prepared using sol gel technique. The X-ray diffraction results showed that the best garnet phase appeared when the sintering temperature was 800 degrees C. Nano-crystalline particles with high purity and sizes ranging from 20 to 100 nm were obtained. It was found that the aluminum substitution had resulted in a sharp fall of the d-spacing when x = 2, which we speculated is due to the preference of the aluminum atoms to the smaller tetrahedron and octahedron sites instead of the much larger dodecahedron site. High resolution transmission electron microscope (HRTEM) and electron diffraction (ED) patterns showed single crystal nanoparticles were obtained from this method. The magnetic measurement gave moderate values of initial permeability; the highest value of 5.3 was shown by sample Y3Fe5O12 at more than 100 MHz which was attributed to the morphology of the microstructure which appeared to be homogeneous. This had resulted in an easy movement of domain walls. The substitution of aluminum for yttrium is speculated to cause a cubic to rhombodedral structural change and had weakened the super-exchange interactions thus a fall of real permeability was observed. This might have created a strain in the sub-lattices and had subsequently caused a shift of resonance frequencies to more than 1.8 GHz when x > 0.5.

Multi-Ferroic Properties of Garnet and Lead Zirconium Titanate Bilayer for Magneto-Optic Spatial Light Modulators

We investigated an analogue modulation of magneto-optic spatial light modulator (MOSLM). For enhancement of the modulation from the voltage-driving MOSLM, magnetostriction and saturation magnetization of magnetic garnet films and piezoelectric constant of PZT films were investigated. The performance was expected to be improved by using Bismuth, Dysprosium and Aluminum substituted Yttrium Iron garnet, which effective magnetic field showed 20 times higher than Yttrium Iron garnet.

Formation of multiferroic thin-film heterostructure (BiAl:YIG/La:PMNT) via a wet chemical process

A novel multiferroic thin-film heterostructure exhibiting both ferromagnetic (FM) and ferroelectric (FE) properties, as well as magneto-optic (MO) and electro-optic (EO) properties, was fabricated via a wet chemical route. Oxide buffer layers were used to allow the growth of ferroelectric lanthanum modified lead magnesium niobate titanate (La:PMNT) layer on top of ferromagnetic bismuth and aluminum substituted yttrium iron garnet (BiAl:YIG). X-ray diffractometer (XRD) analysis confirmed the formation of both crystalline structures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to examine the surface and cross-section morphologies of the resulted heterostructure. Multiferroic properties of the film were investigated.

Phase evolution and magnetic properties of Al substituted yttrium iron garnet nanopowders and plasma-sprayed coatings

Aluminum-substituted yttrium iron garnet (Al-YIG) nanostructured powders were synthesized using a citrate–nitrate gel combustion process. Atmospheric plasma-spray (APS) technique was employed to spray deposit the combustion derived feedstock powders. Nevertheless incongruently melting YIG resulted into a two-phase microstructure, Al-YIG powder resulted into a nanostructured garnet single phase when sprayed through thermal plasma. Room temperature saturation magnetization ( M S) and Curie temperature ( T C) of the Al-YIG powders decreased as a function of increasing Al content. As-sprayed YFe 3.8Al 1.2O 12 coating has a room temperature M S of 6.2 emu/cc and is increased to 7.3 emu/cc after post-deposition heat treatment at 1000 °C/1 h. Microstructural characteristics of single splats were analyzed in order to understand the feedstock effect on deposit.

Enhancement of magneto-optical Faraday rotation by bismuth substitution in bismuth and aluminum substituted yttrium–iron–garnet single-crystal films grown by coating gels

The effect of bismuth substitution on the magneto-optical Faraday rotation of bismuth and aluminum substituted yttrium–iron–garnet (Y3−xBixFe4.2Al0.8O12, x=0 to 2.8) single-crystal films was investigated, where the films were prepared by coating gels involving the constituent metallic ions on single-crystal (GdCa)3(GaMgZn)5O12 garnet plates. The maximum amount of bismuth substitution that yields solely the garnet phase was x=2.5. The onset and the completion temperatures for crystal growth of garnet were decreased by bismuth substitution and were, respectively, 500 and 560 °C for x=2.5. A marked increase in the Faraday rotation θF was observed at heavy substitution x≥2.0 and θF at 3.06 eV (λ=405 nm) was 36.6 deg/μm, but no substantial improvement in the figure of merit for Faraday effect θF/α, where α is the absorption coefficient, was recognized.

Preparation of Polycrystalline Bismuth and Aluminum Substituted Yttrium-Iron Garnet Films by Repetitive Gel Coating on Glass Substrates

Perpendicularly magnetized films of polycrystalline bismuth-and aluminum-substituted yttrium iron garnet were prepared by spin coating a gel on glass substrates. The coated gel was preannealed at temperatures ranging from 300°C to 700°C for 10 minutes and was successively annealed at 700°C for 4 hours in air to form garnet crystals. Thicker garnet films were obtained by repetitive spin coating and the heat treatments stated above. However, magnetic as well as magneto-optical properties of the films were different according to whether preannealing after each coating was done below or above 400°C. This is caused by the formation of carbon-enriched layers on the free surface of each coated gel layer. These interlayers are considered to occur by hydrocarbon decomposition of the solvent and are found to vanish through evacuation of hydrocarbon from the films by preannealing above 400°C.

Bismuth- and aluminum-substituted YIG single-crystal films on modified gadolinium gallium garnet single-crystal substrates

Bismuth- and aluminum-substituted yttrium iron garnet single-crystal films with the nominal composition of Y1.5Bi1.5Fe4.2Al0.8O12 (Bi,Al:YIG) were prepared by spin coating a gel on the (111) plane of (GdCa)3(GaMgZn)5O12 single-crystal garnet plates. Crystallinity of the films varies with temperature and time of heat treatment in air after gel coating. Single-crystal films were obtained at Ta=650 °C for 4 h. The onset temperature for crystal growth is about 560 °C, which is about 400 °C lower than that of liquid-phase epitaxy. The crystal-growth process of single-crystal Bi,Al:YIG films was examined by measuring crystallographic structures as well as the magneto-optical Faraday effect. The internal stress giving rise to magnetic uniaxial anisotropy to align the magnetization normal to the film plane plays an important role for completion of single-crystal growth throughout the film.

Chemical vapor deposition of epitaxial aluminum-substituted YIG for a bubble domain device

Aluminum-substituted yttrium iron garnet Y 3 Al x Fe 5-x O 12 films were epitaxially grown on the