Single Garnet Research Articles

Synthesis, structure and luminescence of Er3+-doped Y3Ga5O12 nano-garnets

A novel Y3(1−x)Er3xGa5O12 nanocrystalline garnet has been synthesized by a sol–gel technique and a complete structural, morphological, vibrational, and optical characterization has been carried out in order to correlate the local structure of the Er3+ ions with their optical properties. The synthesized nanocrystals are found in a single-phase garnet structure with an average grain size of around 60 nm. The good crystalline quality of the garnet structure is confirmed by FTIR and Raman measurements, since the phonon modes of the nano-garnet are similar to those found in the single crystal garnet. Under blue laser excitation, intense green and red visible and 1.5 μm infrared luminescences are observed, whose relative intensities are very sensitive to the Er3+ concentration. The dynamics of these emissions under pulsed laser excitations are analyzed in the framework of different energy transfer interactions. Intense visible upconverted luminescence can be clearly observed by the naked eye for all synthesized Er3+-doped Y3Ga5O12 nano-garnets under a cw 790 nm laser excitation. The power dependency and the dynamics of the upconverted luminescence confirm the existence of different two-photon upconversion processes for the green and red emissions that strongly depend on the Er3+ concentration, showing the potential of these nano-garnets as excellent candidates for developing new optical devices.

Effects of Zr-substitution on microstructure and properties of YCaVIG ferrites

Y2.6−xCa0.4+xZrxV0.2Fe4.8−xO12 (Zrx:YCaVIG) ferrite materials have been prepared by an oxide process. The phase formation and microstructure were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of Zr4+ substitution on phase compositions, sintering properties, microstructures and electromagnetic properties were investigated. The results indicate that all the sintered specimens with different Zr4+ contents show a single garnet structure. The addition of ZrO2 can gradually increase the lattice constant, and lower the sintering temperature and the theoretical density. With the increase of Zr4+ content, the dielectric loss (tanδε) and coercivity (Hc) decrease and then slightly increase, which is due to the variation of the microstructure. But the saturation magnetization (4πMs) shows the opposite variation compared to the former two properties. However, the dielectric constant (εr) remains stable and remanence (Br) monotonically declines. Finally, the specimen of Y2.3Ca0.7Zr0.3V0.2Fe4.5O12 sintered at 1350° possesses the optimum electromagnetic properties: εr=14.8, tanδε=1.35×10−3, 4πMs=1638Gs, Br=596Gs, Hc=0.75Oe and ΔH (ferromagnetic resonance linewidth)=66Oe.

Garnet sector and oscillatory zoning linked with changes in crystal morphology during rapid growth, North Cascades, Washington

Metamorphic garnet with sector zoning in the cores and oscillatory zoning in the rims grew during rapid heating of pelitic rocks in the Chiwaukum Schist. These types of compositional zoning are exemplified by sharp, but low amplitude, boundaries between broad petal-shaped sectors and between narrow concentric zones, respectively. Zoning is most obvious in calcium, which is inversely correlated with iron and magnesium content. Garnet habit inferred from the oscillatory calcium zoning and external morphology indicates a growth transition from early crystal forms with both trapezohedral and dodecahedral forms to later crystal forms dominated by trapezohedral faces. This transition is accompanied by changes in compositional sector zoning and may reflect the roles of local growth dynamics and external forcing mechanisms affecting growth of garnet. Subsequent modification of these textures produced patchy zoning in calcium. Electron backscatter diffraction confirms the inferred crystal growth habits and that compositional zoning occurs within single garnet crystals. Exchange thermobarometry and the peak mineral assemblages indicate that metamorphic conditions reached 640-670 °C at 6.9 kbar. These temperatures are sufficient to allow significant volume diffusion; therefore, preservation of the finely banded compositional zoning in garnet requires rapid heating and cooling. Garnet Sm-Nd ages and indistinguishable zircon U-Pb ages from adjacent orthogneiss bodies confirm that garnet grew rapidly during localized and short-lived heating adjacent to sill-like intrusions of tonalite.

Sub-THz dielectric resonance in single crystal yttrium iron garnet and magnetic field tuning of the modes

The observation of dielectric resonance over the frequency range 40-110 GHz in single crystal yttrium iron garnet (YIG) and its magnetic field tuning characteristics are reported. The dimensions of YIG are appropriately chosen in order to have the dielectric resonance occur at a much higher frequency than the ferromagnetic resonance and avoid any hybrid spin-electromagnetic modes. The dielectric modes are magnetically tunable by 1 GHz with a magnetic field of ∼1.75 kOe. The tuning range and required bias magnetic fields, however, can be controlled with the sample dimensions (or the demagnetization factor Nzz). Theoretical calculations on magnetic field tuning characteristics for the dielectric modes are in reasonable agreement with the data. The theory also predicts a similar magnetic tuning of the dielectric modes in the sub-THz frequency range as well. The dielectric modes that can be tuned with a magnetic field are of importance for the realization of low-loss tunable devices, including resonators, isolators, and phase shifters operating in the sub-THz region.

Implantation of single crystalline iron garnet thin films with He+, B+, and Si+ ions

AbstractThe mechanisms of defect formation in single crystalline epitaxial iron garnet thin films implanted with intermediate energy He+, B+, and Si+ ions have been investigated. X‐ray diffraction and modeling of the implantation process are used to show the effectiveness of defect formation from the electronic energy losses of ion implants decelerating in the target. High temperature diffractometry demonstrates the existence of two centers of disorder in the crystal lattices of ion‐implanted thin films: one due to the defect formation from the electronic energy losses and the other – from the nuclear energy losses of the implant ions.

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.

Structure and Magnetic Properties ofY3−xErxFe5O12(x=0.2,1.0, and 2.0) Thin Films Prepared by Sol-Gel Method

NanoparticlesY3−xErxFe5O12(x=0.2, 1.0, and 2.0) thin films were prepared by sol-gel method and treated at 800, 900, and 1000∘C, respectively, for 2 h. The films have single phase garnet structure and the sizes of particles are in the range of 44 to 83 nm. The magnetic measurements show that the saturation magnetization decreased with increasing of Er concentration for all samples treated at different annealing temperatures. The saturation magnetization increased with the particle size due to the enhancement of the surface spin effect. The coercivity initially decreased forx=1.0and then increased forx=2.0with increasing annealing temperature.

Generation of broadband emission by incorporating N3− into Ca3Sc2Si3O12 : Ce3+ garnet for high rendering white LEDs

Adding Si3N4 into green emitting Ca3Sc2Si3O12 : Ce3+ garnet phosphor generates an additionally red emission band peaking around 610 nm that are assigned to Ce3+ ions having N3− in their local coordination. The excitation spectrum of the red band consists of not only a distinct band at 510 nm of itself but also an intense blue band at 450 nm that belongs to the typical Ce3+ ions with green emission, indicating a notable energy transfer from the green emitting Ce3+ ions to the red ones. The energy transfer significantly enables the achievement of a broad emission spectrum covering a red and green spectral region suitable for generating white light upon a blue light-emitting diode (LED) excitation. The decay patterns of the red and green fluorescence are discussed in relation to the effect of energy transfer. A white LED with high color rendering of 86 and low correlated color temperature of 4700 K is fabricated using the present single garnet phosphor.

Synthesis and optical properties of green to orange tunable garnet phosphors for pcLEDs

Y 3− x Lu x Al 3MgSiO 12:Ce 3+ phosphors were prepared by aqueous sol–gel technique. Samples with 0.25, 0.5, 0.75 and 1 mol-% of Ce 3+ were fabricated and characterized by powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and temperature dependent luminescence to reveal the thermal quenching. Moreover, luminous efficacies (LE), CIE 1931 color points and quantum efficiencies (QE) were calculated and discussed. XRD patterns confirmed the presence of single phase garnet for all samples independent of Ce 3+ concentration and Y/Lu ratio. Phosphors showed broad band emission in the range 500–750 nm. The emission maximum shifts from 555 to 585 nm depending on the Ce 3+ concentration and Y/Lu ratio. Quantum efficiency of the phosphors decreased with rising Ce 3+ concentration and increased with increasing Lu content.

High precision microsampling and preparation of zoned garnet porphyroblasts for Sm–Nd geochronology

Zoned garnet porphyroblasts contain one of the longest continuous records of tectonic processes, with growth histories spanning many millions of years. Well known challenges exist in the physical preparation, purification, and geochronologic analysis of zoned garnets, which have limited the progress and application of this potentially powerful geochronologic tool. Here, we present details of an integrated methodology specifically for the acquisition of high-resolution Sm–Nd geochronologic records from zoned garnets that overcome these challenges. We develop and demonstrate our methods on large test garnets from a shear zone in the Tauern Window in western Austria. Chemically contoured microdrilling permits physical sampling of many discrete age annuli (each as narrow as ~100 μm) within a single garnet. Refined HNO 3/HF/HClO 4 partial dissolution methods cleanse coarse crushed (75–150 μm size) garnet annuli of detrimental inclusions yielding high 147Sm/ 144Nd ratios (0.9 to 4.6) and consequently accurate and precise ages. Experiments on powdered garnet (<75 μm size) gave low 147Sm/ 144Nd (< 0.18) indicating failure to cleanse powders of inclusions. An example of the potentially significant effect of inclusions on age accuracy is presented. Because total garnet sample loss due to crushing and purification can be 40–75% (depending on inclusion density), and because Nd concentrations in garnet are very low (< 1 ppm), resulting Nd mass per annulus can be < 10 ng. Recently developed techniques for the analysis of 1–10 ng Nd samples yield 143Nd/ 144Nd with 10–20 ppm (2 RSD) precision, good enough for <± 1 Ma age precision in most cases when garnet 147Sm/ 144Nd > ~ 1.0. In total, this integrated sampling and analytical protocol permits the acquisition of 3–11 discrete high precision (<±1 Ma) age annuli in a single 2 cm diameter garnet.

Effects of off-stoichiometry and density on the magnetic and magneto-optical properties of yttrium iron garnet films by magnetron sputtering method

Yttrium iron garnet films were deposited on Si and Si/CeO2 substrates by magnetron sputtering method followed by postannealing. By varying the fabrication parameters such as sputtering atmosphere, sputtering power, and annealing atmosphere, single phase garnet films were obtained with different off-stoichiometry and film density. The dependence of cation ratio, magnetic and magneto-optical characteristics, and absorption coefficient were systemically investigated. The results reveal that a proper oxygen pressure in both sputtering and annealing process give rise to a small cation ratio of (Fe2+ or Fe4+)/Fe3+, thus is beneficial to obtain large saturation magnetization, large Faraday rotation, and small optical absorption. The sputtering power can also affect the properties of the film through changing the film density. Our results indicate that the properties of sputtering deposited yttrium iron garnet (YIG) film can be easily tuned and optimized by modifying the off-stoichiometry and density of the film, thus provides flexibility to fabricate YIG film for extensive applications.

Structural and size dependent magnetic properties of single phase nanostructured gadolinium-iron-garnet under high magnetic field of 32 tesla

Here we report the single phase nanostructured Gd3Fe5O12 garnets with different grain sizes (bulk, 75, 47, 35, and 22 nm) were prepared by ball milling for various milling times. Both the average grain size and the lattice parameter were estimated from the x-ray diffraction line broadening. The F57e Mössbauer spectra were recorded at 300 and 77 K for the samples with different grain sizes clearly evidenced the formation of Fe2+ ions induced by milling and the content of Fe2+ increases with milling time. At 4.2 K, a significant increase in saturation magnetization (+11%) has been observed for the 47 nm particles. The magnetization is strongly applied field dependent and no saturation effect is observed even at fields as high as of 320 kOe. The results presented here have been explained in terms of the key role played by the Fe2+ ions.

Fabrication and characteristics of one-dimensional magnetophotonic crystals for magneto-optic spatial light phase modulators

We prepared the reflection type magnetophotonic crystals (R-MPC) to enhance the magneto-optic property of magneto-optic spatial light phase modulator (MOSLM). Magnetophotonic crystals have a localized wavelength by using a defect layer in which the magneto-optic property can be increased tremendously. By the calculation, it was revealed clearly that Kerr rotation can be enhanced with increasing the repetition number (k) which is the number of dielectric layer. In this study, Dy1.0Bi1.5Y1.0Fe3.8Al1.2O12 (DyBi:YIG) garnet material, of which Faraday rotation angle is about −3 deg/μm, was utilized as a defect layer. At the designed wavelength of 532 nm and k=5, SGGG/[SiO2/Ta2O5]2/DyBi:YIG/[SiO2/Ta2O5]k structure fabricated with garnet thickness of 347.6 nm showed Kerr rotation angle of 26° and reflectivity of 0.2% which is coincident considerably with the results (θk=30° and R=0.59%) calculated by the matrix approach method. The fabricated R-MPC-MOSLM structure exhibited the magneto-optic property of about 25 times higher than single garnet film in consideration of the thickness of magneto-optic material.

High resolution Sm–Nd garnet geochronology reveals the uneven pace of tectonometamorphic processes

Chemically zoned garnets provide a record of the changing conditions within the tectonically evolving crust where metamorphic mineral growth occurs. Recent advances in Sm–Nd geochronology of zoned garnets now permit the measurement of a higher resolution temporal record than previously attainable. Here, we present precise (< ± 0.7 million years) Sm–Nd ages from 12 concentric growth zones within a single large garnet from the Austrian Alps. Within a total growth span of 7.55 ± 0.52 (2 SD) million years, the data reveal two brief distinct pulses of accelerated growth (at least 5 times faster than the background growth rate). These pulses correlate with compositional features in the zoned garnet that are indicative of growth in the presence of abundant fluids or abrupt P– T changes. These data show that tectonometamorphic processes leading to garnet growth (such as exhumation, fluid flow, and/or heating) were pulse-like in nature, rather than slow and steady, during the waning stages of the Alpine orogeny 28–20 million years ago.

Three metamorphic events recorded in a single garnet: Integrated phase modelling, in situ LA‐ICPMS and SIMS geochronology from the Moine Supergroup, NW Scotland

Abstract In situ LA‐ICP‐MS monazite geochronology from a garnet‐bearing diatexite within the Moine Supergroup (Glenfinnan Group) NW Scotland records three temporally distinct metamorphic events within a single garnet porphyroblast. The initial growth of garnet occurred in the interval c. 825–780 Ma, as recorded by monazite inclusions located in the garnet core. Modelled P–T conditions based on the preserved garnet core composition indicate an initially comparatively high geothermal gradient regime and peak conditions of ∼650 °C and 7 kbar. Monazite within a compositionally distinct second shell of garnet has an age of 724 ± 6 Ma. This is indistinguishable from a SIMS age of 725 ± 4 Ma obtained from metamorphic zircon in the sample, which is interpreted to record the timing of migmatization. This second stage of garnet growth occurred on a P–T path from ∼6 kbar and 650 °C rising to ∼9 kbar and 700 °C, with the peak conditions associated with partial melting. A third garnet zone which forms the rim contains monazite with an age of 464 ± 3 Ma. Monazite in the surrounding matrix has an age of 462 ± 2 Ma. This corresponds well with a U–Pb SIMS zircon age of 463 ± 4 Ma obtained from a deformed pegmatite that was emplaced during widespread folding and reworking of the migmatite fabric. The P–T conditions associated with the final phase of garnet growth were ∼7 kbar and 650 °C. The monazite ages coupled with the phase relations modelled from this multistage garnet indicate that it records two Neoproterozoic tectonothermal events as well as the widespread Ordovician Grampian event associated with Caledonian orogenesis. Thus, this single garnet records much of the Neoproterozoic to Ordovician thermal history in NW Scotland, and highlights the long history of porphyroblast growth that can be revealed by in situ isotopic dating and associated P–T modelling. This approach has the potential to reveal much of the thermal architecture of Neoproterozoic events within the Moine Supergroup, despite intense Caledonian reworking, if suitable textural and mineralogical relationships can be indentified elsewhere.

Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm–Nd and zircon U–Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm–Nd ages of 126.1±2.0 and 122.6±2.0 Ma date crystal growth. Integration of the garnet ages with U–Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150 Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134 Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126 Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123 Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95 Ma. Phase diagram sections constrain orthopyroxene assemblages to < 0.6 GPa @ 650 °C, peak garnet granulite facies metamorphic conditions to 680–815 °C @ 1.1 – 1.4 GPa, and a P– T path with a P increase of ≥ 0.5 GPa. These sections are compatible with water contents ≥ 0.28 wt.%, local dehydration during garnet granulite metamorphism, and < 0.3 GPa P increases during garnet growth. Results demonstrate the utility of integrated U–Pb zircon and Sm–Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern Fiordland, must have occurred prior to 126 Ma, that loading occurred at a rate of ca. 0.06 GPa/m.y., and that garnet granulite metamorphism lasted 3–7 m.y. Locally-derived partial melts formed and crystallized in considerably less than 10 and perhaps as little as 3 m.y.

Effects of In-substitution on the microstructure and magnetic properties of Bi-CVG ferrite with low temperature sintering

[Y 1.05Bi 0.75Ca 1.2](Fe 4.4− x In x V 0.6)O 12(In x :Bi-CVG) ferrite material has been prepared successfully by a solid-state reaction method. The effects of In 3+ substitution and sintering temperatures on the bulk density, microstructure and magnetic properties are performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), materials automatic test system (MATS) and microwave ferrite parameters meter. The results show that In 3+ can lower the sintering temperatures and enhance the magnetic properties of Bi-CVG ferrite. Besides, all sintered specimens with different In 3+ contents show a single garnet crystal structure. The specimen of [Y 1.05Bi 0.75Ca 1.2](Fe 4In 0.4V 0.6)O 12 sintered at 1075 °C shows homogenous distribution of grain size and densified microstructures. The ferromagnetic resonance linewidth (Δ H) has an increase with In 3+ contents. Additionally, the sample has the optimum magnetic properties: ρ=5.23 g/cm 3, B r =31.3 mT, H c=378.8 A/m, 4πM s =506.2×10 −4 T.

Garnet reaction rims from the breakdown of Staurolite in polymetamorphic micashists from the Rappold complex, Austroalpine basement, Eastern Alps

In polymetamorphic pelites of the Rappold complex in the Wolz crystalline basement (Eastern Alps) reaction rim garnets at staurolite-quartz interfaces (type I) and single grain garnets along previous staurolite-white mica interfaces (type II) were formed. The garnet reaction rims were formed during the Cretaceous amphibolite facies metamorphic overprint of the pre-existing mineral assemblages comprising garnet, staurolite, and kyanite from an amphibolite facies metamorphic event probably of Variscian age. The newly formed garnet may take the form of reaction rims along the margins of large pre-existing staurolite blasts. The initial growth increments of garnet have low grossular content, and reaction rim growth was controlled by the transfer of Fe, Mg and Mn components from the staurolite-garnet interface to the quartz-garnet interface. Later garnet growth increments have relatively high grossular content due to consumption of matrix plagioclase, which was destabilized by successive pressure increase. The grossular content of newly formed garnet shows systematic increase towards sites where plagioclase breaks down indicating that transport of calcium through the matrix was sluggish. On the basis of reaction microstructures it is demonstrated that the mineral assemblage garnet + kyanite + biotite + paragonite was formed at the conditions of eo-alpine amphibolite facies overprint while staurolite and plagioclase broke down successively with increasing pressure.

Synthesis of Nd:YAG nanopowder using the citrate method with microwave irradiation

Abstract Nd:YAG nanopowders were prepared using the Pechini process with microwave irradiation ( MWs ). A reference sample was also prepared using conventional heating. XRD pattern analysis showed that nanopowder obtained by means of conventional heating and calcination for 1 h at 900 °C has a structure made up of the garnet phase together with the hexagonal phase that disappeared after two additional hours of thermal treatment. The MWs powder calcined for 1 h consists of the single garnet phase. SAXS data analysis indicated that nanoparticles are characterized by a sharp interface. TEM investigation showed crystalline particles with remarkable agglomeration in both samples, although a more homogeneous size of particles was evident in the MWs sample as compared to the reference sample. The rate, the calcination time and the quality of the powder obtained make the Pechini process with microwave irradiation an attractive alternative procedure to conventional YAG preparation methods.

Ion microprobe analysis of oxygen isotopes in garnets of complex chemistry

Accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias, a component of which depends on the cation chemistry of the analyzed mineral. In this study, 26 garnet standards (including 14 new standards) that span the compositional range of pyrope, almandine, grossular, spessartine, and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets. All analyses were normalized to a single master garnet standard (UWG-2) before bias from cation composition was considered. Bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets. Bias is correlated with molar volume in garnets of all compositions in this study. Although this correlation is suitable as a correction scheme for bias, a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed. This method reproduces the bias of all but one standard to within a range of 0.4‰, an accuracy that is on the same order as the reproducibility (± 0.3‰, 2 S.D.) of the master garnet standard UWG-2, but that remains an independent source of error. The new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic, zoned skarn garnet from the Adirondack Mountains. While previous analyses were at the mm-scale, the new data resolve a gradient of δ 18O of 2.1‰ over 16 µm. If experimentally derived diffusion coefficients are correct, these new results show that granulite-facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 Myr.