Small optical magnetic-field sensor that uses rare-Earth iron garnet films based on the faraday effect

Highly accurate optical magnetic-field probe sensors that use iron garnet films have been developed. New probe-type sensors were designed with a confocal optical system. A new garnet composition, Bi(0.98)Gd(0.92)La(0.03)Y(1.07)Fe(4.72)Ga(0.28)O(12), was found that shows high temperature stability for a sensitivity of less than 2.0% from -20 to +80 degrees C. The linearity error of the sensor output was within 1.0% for alternating magnetic fields from 0.3 to 42 mT. An optical current transformer that uses the proposed sensor has an ac linearity of 1.0% for input current up to nearly 300 A. The sensor realized high performance in actual use.     

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.     

Optical nonreciprocal devices with a silicon guiding layer fabricated by wafer bonding

Optical nonreciprocal devices with a silicon guiding layer fabricated by wafer bonding are proposed. The optical nonreciprocal devices are composed of a magneto-optic waveguide with a magnetic garnet/Si/SiO2 structure. Nonreciprocal characteristics are obtained by an evanescent field penetrating into the upper magnetic garnet cladding layer. Several kinds of the optical nonreciprocal device are investigated with the magneto-optic waveguide and designed at a wavelength of 1.55 microm. As a preliminary experiment, wafer bonding between Gd3Ga5O12 and Si was studied. Wafer bonding was successfully achieved with heat treatment at 220 degrees C in H2 ambient.     

Thermoluminescence of MgSO4 doped with Eu and P impurities

CaSO4:Eu, MgSO4:Eu and MgSO4:Eu,P phosphors have been prepared and their thermoluminescence (TL) characteristics were studied. A main glow peak due to Eu2+ ions is seen at approximately 146 degrees C and 440 nm and glow peaks at approximately 145 degrees C, approximately 190 degrees C, approximately 260 degrees C and approximately 360 degrees C for 590 nm and 625 nm wavelengths are identified as Eu3+ ion emissions in MgSO4:Eu. Emission spectra in MgSO4:Eu and the MgSO4:Eu,P show that the MgSO4:Eu3+ glow peak at 260 degrees C for 590 nm and 625 nm shifts to 280 degrees C with enhanced intensity while the Eu2+ ion glow peak at 146 degrees C remains but with reduced intensity. The main glow peak at approximately 146 degrees C and 440 nm from Eu2+ ions shows significant difference from the characteristic glow peaks of Eu3+ ions. It is observed that the wavelength of the Eu2+ ion glow peak is inversely proportional to the radius of the cation of the host sulphate in alkaline-earth sulphate phosphors. By contrast the wavelengths of the Eu3+ ion glow peaks remain unchanged in different sulphates. Besides, the glow curve at approximately 146 degrees C obtained using a conventional blue sensitive reader shows simply the first order kinetics. It is concluded that the luminescence centres and distribution of traps related to Eu2+ ions are different from that of Eu3+ ions in MgSO4:Eu and MgSO4:Eu,P phosphors.     

Preparation,spectroscopic properties and enhanced luminescence of Tb<Superscript>3+</Superscript>-doped LuAG phosphors and transparent ceramics by introduction of Sc<Superscript>3+</Superscript>

Tb-doped LuAG(lutetium aluminum garnet) and LuSAG(lutetium scandium-aluminum garnet) precursors were synthesized through a co-precipitation process, using ammonium hydrogen carbonate as precipitator. Single-phase cubic LuAG/Tb and LuSAG/Tb phosphors were obtained after calcination at 1000 and 1200 °C, respectively. These powders could be easily sintered into corresponding transparent LuAG/Tb and LuSAG/Tb ceramics in H₂ atmosphere at 1850 °C. The PL excitation and emission spectra were recorded for both phosphors and ceramics. Emission spectra of all materials were found to be typical for Tb³⁺, resulting from radiative relaxation of D level. Both the Tb-doped LuSAG phosphors and ceramics show higher efficient luminescence than LuAG , especially the transparent Tb-doped LuSAG ceramic shows about 150% higher luminescence intensity than transparent Tb-doped LuAG ceramic.     

Epitaxial growth and annealing control of FMR properties of thick homogeneous Ga substituted yttrium iron garnet films

Homogeneous, 30 μm to 70 μm thick Ga substituted yttrium iron garnet films have been grown on Y or Al substituted gadolinium gallium garnet substrates having lattice parameters matched to that of the films. Resonance field and FMR linewidth measurements as a function of frequency and annealing experiments revealed that the magnetization and cubic anisotropy of the films are identical to data from flux grown bulk single crystals, the FMR losses of the films are only slightly higher. For films grown with supercooling ΔT < 50 °C a negative, growth induced, uniaxial anisotropy was found which could be removed by annealing in air at 1100 °C. A compensation of the temperature drift of the FMR frequency can be adjusted in the Ga substituted films by changing the frozen-in Ga-Fe cation distribution by annealing and quenching from different temperatures > 800 °C.     

Uptake properties of Ni2+ by nCaO.Al2O3.2SiO2 (n=1-4) prepared from solid-state reaction of kaolinite and calcite

A series of nCaO.Al2O3.2SiO2 samples (n=1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 degrees C for 24 h. All the samples were X-ray amorphous after firing at 600-800 degrees C but had crystallized by 900 degrees C. The main crystalline phases were anorthite (n=1), gehlenite (n=2 and 3) and larnite (n=4). The uptake of Ni2+ by nCaO.Al2O3.2SiO2 samples fired at 800 and 900 degrees C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 degrees C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 degrees C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO.Al2O3.2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.     

Nd optical multisites in the Ca3(Nb,Ga)2Ga3O12 laser garnet crystal

Laser excited site-selective luminescence of Nd³⁺ ion in the Ca₃(Nb,Ga)₂Ga₃O₁₂ garnet crystal has been investigated for the and transitions. Six main non-equivalent crystal field sites were detected in the garnet. The crystal splitting scheme of the and manifolds was obtained for each Nd³⁺ site. Energy transfer between Nd³⁺ sites was observed by using time resolved spectroscopy.     

Synthesis and characterization of photoluminescent cerium-doped yttrium aluminum garnet

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce³⁺) is synthesized by sol-gel method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also used. The purified crystalline phases of YAG and YAG:Ce were obtained at 1000 °C. The maximum average grain size is about 20-23 nm for undoped samples and 28-34 nm for doped samples. The crystalline YAG:Ce emission shows one peak in the range 480-535 nm with the maximum near 520 nm. Photoluminescence (PL) intensity of 5d → 4f transition of Ce³⁺ increased with increasing annealing temperature. With increasing the concentration of Ce³⁺, the photoluminescence peak shifts towards the red region.     

Radiation resistance and chemical stability of yttrium aluminum garnet

The radiation resistance and chemical stability of yttrium aluminum garnet doped with short-lived ²⁴⁴Cm for accelerated accumulation of radiation damages was studied. Two garnet samples of the stoichiometry Y_2.8853Cm_0.1024Pu_0.0092Al₅O₁₂, containing ～4 wt % Cm with 70% content of ²⁴⁴Cm, were synthesized. The ceramics consist of the target phase of the garnet structure and a small amount of corundum. The chemical stability of the freshly prepared sample in water was studied (MCC-1 test, 90°C). The Cm leach rate is ～10^?2 g m^?2 day^?1, and that of Al and Y, ～10^?3 g m^?2 day^?1. The garnet became fully X-ray amorphous owing to self-irradiation in 530 days at the accumulated dose of 4.0 × 10¹⁸ α-disintegrations per gram, or 0.3 displacement per atom. After the destruction of the garnet structure, the Cs leach rate from the matrix 14 days after the start of the experiment increased by a factor of 10, and that of Y, by a factor of 60 relative to the freshly prepared ceramics.     

石榴石型磁光存储材料

稀土铁石榴石薄膜被认为是最具应用前景的下一代磁光记录材料。稀土铁石榴石薄膜具有高的矫顽力、良好的热、化学稳定性及强的磁光效应等特点；特别是当Ｂｉ３＋和Ｃｅ３＋离子部分取代石榴石结构中的稀土离子后，可以极大地增强其磁光效应。本文就磁光记录的原理、磁光存储材料、稀土铁石榴石磁光薄膜的制备及其如何降低石榴石薄膜中的晶界噪声等问题作了一些探讨。     

Fluorescence switch in red-phase polydiacetylene films and vesicles upon thermal cycles

The switch phenomena of thermochromism of red-phase polymerized PCDA (10,12-pentacosadiynoic acid) Langmuir-Schaefer (LS) films and vesicles were investigated in situ during repeated heating and cooling processes between 25 degrees C and 70 degrees C. During repeated thermal cycles, the solid-supported LS films exhibited switch phenomena in both the visible and fluorescent spectra, that is, the colorimetric response (CR) of the PCDA LS films was ca. 80% at 70 degrees C but is ca. 50-60% at 25 degrees C with an increase of fluorescent intensity in the cooling process and a decrease in the heating process. On the other hand, the PCDA vesicles exhibited such phenomenon only in the fluorescent spectra, that is, the CR of the PCDA vesicles was constant as ca. 100% after being stable red form with the same trend in the fluorescent intensity. The changes in molecular configuration revealed by in situ Fourier transform infrared (FTIR) were in good agreement with the trend of fluorescence emission upon repeated thermal stimuli rather than that of visible absorption.     

Device optimization of CO2 gas sensor using planar technology

A planar type Li+ ion based potentiometric CO2 micro gas sensor of size 2 x 3 mm has been fabricated on alumina substrate by combining thin and thick film technology. The heater, electrodes and electrolyte were deposited by thin film deposition technique and the sensing and reference electrodes were printed by silk screen printing technology. The optimal thickness and sintering temperature of electrolyte are 1.2 microm and 775 degrees C. The sensor with Li2CO3 and 20 mol% BaCO3 not only exhibits a good Nernstian behavior but also consistent results over a long time at 450 degrees C in dry as well as 70% RH humidity condition between 160-5000 ppm CO2 concentrations. The spreading effect of the sensing and reference materials was controlled by the addition of Al2O3:B2O3 (1:2 mol%) glass.     

Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor

The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.     

Anomalous elastic properties of RF-sputtered amorphous TeO2+x thin film for temperature-stable SAW device applications.

The anomalous elastic properties of TeO2+x thin films deposited by rf diode sputtering on substrates at room temperature have been studied. The deposited films are amorphous, and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy confirms the variation in the stoichiometry of TeO2+x film from x=0 to 1 with an increase in the oxygen percentage in processing gas composition. The elastic parameters of the films in comparison to the reported values for TeO2+x single crystal are found to be low. However, the temperature coefficients of elastic parameters of all deposited films exhibit anomalous behavior showing positive values for TC(C11) in the range (32.0 to 600.0)x10(-4) degrees C(-1) and TC(C44)=(35.0 to 645.5)x10(-4) degrees C(-1) against the negative values TC(C11)=-2.7x10(-4) degrees C(-1) and TC(C44)=-0.73x10(-4) degrees C(-1) reported for TeO2+x single crystal. The variation in the elastic parameters and their temperature coefficients is correlated with the change in the three-dimensional network of Te-O bonding. The anomalous elastic properties of the TeO2+x films grown in 100% O2 are useful for potential application in the design of temperature stable surface acoustic wave devices.     

Rapid synthesis and characterization of maghemite nanoparticles

Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe203-SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.     

Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet

Complex oxide films stabilized by epitaxial growth can exhibit large populations of point defects which have important effects on their properties. The site occupancy of pulsed laser-deposited epitaxial terbium iron garnet (TbIG) films with excess terbium (Tb) is analyzed, in which the terbium:iron (Tb:Fe)ratio is 0.86 compared to the stoichiometric value of 0.6. The magnetic properties of the TbIG are sensitive to site occupancy, exhibiting a higher compensation temperature (by 90 K) and a lower Curie temperature (by 40 K) than the bulk Tb₃Fe₅O₁₂ garnet. Data derived from X-ray core-level spectroscopy, magnetometry, and molecular field coefficient modeling are consistent with occupancy of the dodecahedral sites by Tb³⁺, the octahedral sites by Fe³⁺, Tb³⁺ and vacancies, and the tetrahedral sites by Fe³⁺ and vacancies. Energy dispersive X-ray spectroscopy in a scanning transmission electron microscope provides direct evidence of Tb_Fe antisites. A small fraction of Fe²⁺ is present, and oxygen vacancies are inferred to be present to maintain charge neutrality. Variation of the site occupancies provides a path to considerable manipulation of the magnetic properties of epitaxial iron garnet films and other complex oxides, which readily accommodate stoichiometries not found in their bulk counterparts.     

Effect of the composition of starting yttrium aluminum hydroxide sols on the properties of yttrium aluminum garnet powders

A technique has been developed for the synthesis of yttrium aluminum garnet sols aggregationstable in water as a dispersion medium. Depending on the type of precursor used, the temperature of yttrium aluminum garnet formation varies from 900°C to 1100°C. We have obtained yttrium aluminum garnet nanopowders with an average particle size from 40 to 300 nm, depending on the aluminum yttrium hydroxide hydrosol synthesis procedure and annealing temperature.     

An X-band, high power dielectric resonator oscillator for future military systems

A 9.0-GHz dielectric resonator oscillator (DRO), generating a CW output power of 2.5 W at room temperature, has been designed and fabricated using a high-power GaAs MESFET and a dielectric resonator (DR) in a parallel feedback configuration. The oscillator exhibited a frequency stability of better than 130 ppm, without any temperature compensation, over the range -50 degrees C to +50 degrees C. The output power varied from +35 dBm (3.2 W) at -50 degrees C to +33 dBm (2 W) at +50 degrees C. The single-sideband phase noise levels were measured and found to be -105 and -135 dBc/Hz, at 10- and 100-kHz carrier offset frequencies, respectively. The oscillator output was then fed into a single-stage high-power MESFET amplifier, resulting in a total RF power output of 6.5 W. The overall DC to RF conversion efficiency of the 6.5-W unit was approximately 15.3%     

Substrate Effect on the Ferromagnetic Resonance Linewidth in Yttrium Iron Garnet Epilayers

The structural perfection of gadolinium gallium garnet (GGG) substrates was shown to have a strong effect on the ferromagnetic resonance (FMR) linewidth in the yttrium iron garnet (YIG) epilayers. The most detrimental imperfections are dislocation pileups and iridium inclusions. A substrate preparation procedure was proposed which ensures the growth of YIG layers 4.7–5 m in thickness, with an FMR linewidth of 24–40 A/m. YIG layers up to 70 m in thickness were grown using lattice-matched iron garnet buffer layers.