Rare-earth Garnets Research Articles

Synthesis and characterization of yttrium iron oxide/PPy nanocomposites for supercapacitor application by chemical oxidative polymerization method

ABSTRACT Polypyrrole (PPy)/Yttrium Iron oxide (YIG) nanocomposite was synthesized by the chemical oxidation polymerization method. Yttrium iron oxide is also known as iron yttrium oxide or yttrium iron garnet denoted as YIG (Y3Fe5O12). YIG is a familiar material among the rare earth garnets and is also commonly used in electronic devices. Fourier transform infrared (FT-IR) spectroscopy analysis reveals the strong interaction between PPy and YIG nanoparticles. The crystal structure for the PPy and PPy nanocomposites is observed by X-ray Diffraction (XRD) and the average crystalline size calculated by Scherrer’s formula for PPy/n-YIG is 27.47 nm. Surface morphology of the samples identified by scanning electron microscopy. Optical properties were studied by UV–Vis spectroscopy. From the 2-probe method, AC electrical conductivity for n-YIGPPy is found to be 1.05 × 10−5 S/cm, higher than that of the polypyrrole. The electrochemical performance of PPy and YIG/PPy nanocomposites was observed by cyclic voltammetry (CV). The combination of optical, electrical properties of YIG/PPy nanocomposites suits supercapacitor applications.

Effects of Fe2+ on dielectric and magnetic properties in rare earth garnet type high entropy oxides

Given the important role played by the valence state of the transition metal in determining material this paper investigates the effect of Fe2+ content on the structure and dielectric properties of garnet-structured high entropy oxides (Y0.2Eu0.2Er0.2Dy0.2Lu0.2)3(Al0·5Fe0.5)5O12 through Fe2+ doping. The results of XPS and Mӧssbauer spectra showed that the Fe2+ content in the tetrahedron increased with Fe2+ doping. With increasing Fe2+ content, the dielectric constants gradually increased, and the maximum dielectric constant reached 2.78 × 104 at 100 Hz under 30 °C. The analysis of the AC impedance spectrum and electrical conductivity revealed that the difference between the activation energy of grain boundary and grain conductivity resulted in increased dielectric constants of the samples. In addition, the doping of Fe2+ increased the maximum magnetization of the samples. This work provides a new idea for designing giant dielectric materials and magnetic materials with a high entropy strategy.

Engineering atomic size mismatch in Pr3+, La3+ codoped Lu3Al5O12 garnet single crystals for tailored structure and functional properties

This study provided the first in-depth investigation of the effects of large dopant incompatibility (Pr3+ and La3+ ions) on the small host lattice element (Lu3+) in Lu3Al5O12 (LuAG) single crystal. The growth of such complex crystals from the melt presented many challenges. By engineering the ionic radius ratio of RE- and M-site cations, a single-crystal phase stabilized by configurational entropy was achieved. This investigation elucidated the crystallization behavior of configurationally disordered rare-earth aluminum garnet oxide (Lu1−x−yPrxLay)3Al5O12 from the melt and characterized its functional properties, including microstructural, optical, photoluminescence, and scintillation properties, between 5 and 300 K. Relaxation of the imposed strain energy led to local perturbations and destabilization of the garnet structure. Multielemental EDS mapping, micro-Raman spectroscopy, and thermoluminescence revealed the mechanism by which atomic size mismatch drove a smooth transition from the garnet to the perovskite phase in high entropy garnets. The optical, photoluminescence, and scintillation measurements provided fundamental insights into property changes driven by incompatibility doping. Standard and modified Judd-Ofelt theory analysis of absorption spectra determined the phenomenological Judd-Ofelt parameters Ωλ and radiative lifetimes. Atomic size mismatch engineering offers a promising approach to overcoming the limitations of conventional eutectic synthesis methods.

X-ray excited optical luminescence from lanthanide ions in double phosphate and double silicate crystalline hosts

X-ray Excited Optical Luminescence (XEOL) from rare earth doped whitlockite phosphates and silicate garnets [Ca9La(PO4)7 and Ca9Lu(PO4)7, doped with 1 mol% Ce3+; Ca3Sc2Si3O12, doped with 0.5 mol% Pr3+, 1 mol% Eu3+ and 1 mol% Tb3+], was obtained upon X-ray excitation with a tunable synchrotron light source. Excitation at photon energies across the M5,4-edge of the dopants reveals additional information not normally obtainable with conventional UV/visible or an X-ray line source (Al Kα). It is found that despite the low concentration, photoluminescence yields excited with photon energy at the M5,4-edge of the rare-earth dopant can positively and negatively affect the overall energy transfer to the optical center. The implication of these observations is discussed. The application of XEOL in the investigation of X-ray scintillators is illustrated.

Regulatable thermoelectric effect in heterostructured ferromagnetic nanomultilayers

Thermoelectric materials and devices have the potential to directly convert heat into electricity, making them crucial for advancing the energy structure system and achieving the dual-carbon goal. However, the conventional methods of preparing thermoelectric materials and designing devices still face significant challenges, limiting the widespread application of thermoelectric technology. Ferromagnetic metal heterostructured nanomultilayers play a crucial role in generating, transporting, and detecting spin currents. Studying the properties and physical mechanisms of spin-dependent magnetic-thermal-electrical effects in the core material is essential for advancing spin thermoelectrics in the future. In this paper, we investigate the spin-related thermoelectric effects in artificial spin-valve heterostructured nanomultilayers. The spin-current generating layer is made of rare-earth garnet, while the spin-current detecting layer consists of ferromagnetic alloy thin films with different compositions of Fe–Co. It is being investigated to obtain thermal voltage signals with excellent stability and high resolution as well as to achieve the amplification and positive/negative adjustment of these signals. This study can serve as a reference for designing thermoelectric materials and aiding in the development of future high-efficiency spin-thermoelectric conversion devices.

Stuffed Rare-Earth Garnets.

We report the synthesis and magnetic characterization of stuffed rare-earth gallium garnets, RE3+xGa5-xO12 (RE = Lu, Yb, Er, Dy, Gd), for x up to 0.5. The excess rare-earth ions partly fill the octahedral sites normally fully occupied by Ga3+, forming disordered pairs of corner-shared face-sharing magnetic tetrahedra. The Curie-Weiss constants and observed effective moments per rare-earth are smaller than are seen for the unstuffed gallium garnets. No significant change in the field-dependent magnetization is observed but missing entropy is seen when integrating the heat capacity down to 0.5 K.

Rare-earth gallium garnet (RE3Ga5O12, RE = Eu, Gd, Dy, Er, and Yb) self-assembled nanostructure based battery type electrodes for efficient asymmetric supercapacitor applications

The modern energy crisis has recently prompted researchers to seek alternatives. In this context, using electrochemical energy resources for energy conversion and storage drew considerable interest. Herein, a new attempt at implementing a series of semiconducting rare earth gallium garnets (REGGs; RE = Eu, Gd, Dy, Er, and Yb)/RE3Ga5O12 is employed for energy storage application. Garnets, an active host for rare earth ions with significant physical and chemical features, are expected to be promising electrode materials for supercapacitors. REGGs are synthesized via the gel matrix method. The phase purity and morphology of synthesized garnets were confirmed using XRD, Raman, XPS, FESEM, and TEM analysis. All synthesized rare earth gallium garnets show a cubic structure and manifest coral reef-like structures with minor variations. The surface area of the material is calculated using BET analysis. The electrochemical performance of the material is evaluated with CV, GCD, and EIS analysis in 3 M KOH. Eu3Ga5O12 exhibits a notable specific capacity of 303 C g−1 (84.1 mA h g−1) at 1 A g−1 compared to other rare earth gallium garnets with sustained cyclic stability of about 80.12 % even after 5000 cycles. The practical applicability of the synthesized Eu3Ga5O12 material is investigated by analyzing its performance in asymmetric supercapacitor devices. The fabricated device exhibited a maximum energy and power density of 39.06 W h kg−1 and 1125 W kg−1 at 1 A g−1, respectively. The exquisite features of rare earth gallium garnets with extended electrochemical performance indicate their potential to be a promising electrode material for energy storage applications.

Diffusion behaviour and corrosion rate of rare earth monosilicate-based EBCs under CMAS exposure

The thermochemical corrosion behaviour of different rare earth (RE)-based (Yb, Lu and Er) environmental barrier coatings (EBCs) between 1 and 48 h in low calcium–magnesium–aluminosilicate (CMAS) load environments at 1300 °C was studied. The EBCs were coated on reaction-bonded SiC–B4C substrates using the dip-coating method. Each coating is composed of a dense RE2SiO5-based bottom coat and a porous RE2O3 topcoat. The microstructures and compositions of the corroded samples were examined using scanning electron microscopy and energy dispersive spectroscopy. CMAS infiltrated the topcoat through pores and cracks, settled in these defects, and dissolved in the neighbouring coating areas to precipitate as a Ca–Mg–Si–RE garnet. The diffusion coefficients of Ca and Si in the CMAS–EBC corroded specimens were calculated. Yb and Lu silicates have the lowest diffusion coefficient values, whereas Er silicate has the highest values. The formed garnet filled the pores and inhibited further diffusion of corrosive species in the coat. The corrosion rates were calculated based on the physical properties of the coat and found to be lower than those of coatings produced using atmospheric plasma spraying. The diffusion coefficient and corrosion rate were successfully used to evaluate various corrosion-resistant coatings. The results show that single-layer dip-coated Yb silicate is a cost-effective CMAS-resistant RE-based EBC.

Magnetic ordering in sol-gel-based Tm3Fe5O12 thin film

In the quest to utilize rare-earth garnets (ReIG) with perpendicular magnetic anisotropy (PMA) in futuristic spintronics, the attention turned towards iron garnet thin films. Among this family, the one candidate is Tm3Fe5O12 (TmIG) that manifests PMA with excellent Gilbert damping, making this material a potential candidate in magnonics devices. Here, we report a cost-effective deposition approach of the TmIG thin films deposited on a thermally oxidized Si(100) substrate. The homogeneous TmIG (≈22 nm) thin film shows a roughness of ≈1.5 nm. The magnetic properties of thin films indicating the compensation temperature 15 K. Experimental findings present a method for the deposition of TmIG thin films, which is a potential candidate for fabricating futuristic compact devices.

Interlayer antiferromagnetic coupling in Tb3Fe5O12/Y3Fe5O12 bilayers

The interlayer antiferromagnetic (AFM) coupling between thin films plays a significant role in the application of spintronics and magnetic memory devices. Previously, we observed AFM coupling phenomenon at low temperatures in rare-earth iron garnet bilayers epitaxially grown on Y3Al5O12 substrates. Here, we report a detailed study on the impacts of various factors, including temperature, crystallographic orientation, and layer thickness, on the AMF coupling and magnetization reversal behavior of such a bilayer system. A simple energy model qualitatively described the coupling behavior of the two layers during the magnetization reversal process. The interlayer coupling strength was calculated by measuring the minor magnetic hysteresis loops. The current results can serve as a reminder for future research on interlayer AFM coupling phenomena and highlight the potential of manipulating the magnetic properties in rare-earth garnet bilayers for spintronics studies and other applications.

The thickness effect on the compensation temperature of rare-earth garnet thin films

The anomalous Hall effect measurements are used to probe the magnetization reversal of terbium iron garnet (TbIG) thin films at different temperatures. The compensation temperature (Tcomp) of TbIG thin films is revealed, and the film thickness effect on the Tcomp is studied. The results indicate a rise of Tcomp along with decreasing film thickness. We postulate two possible origins for the observed behavior, namely interfacial element diffusion and strain effects between TbIG films and Gd3Ga5O12 substrates. The results have implications for the study of spintronic devices based on ultrathin rare-earth iron garnet thin films.

Heterogeneity effects of Tm upconversion emission in Mo, Tm codoped rare-earth garnets

Heterogeneity effects of Tm upconversion emission in Mo, Tm codoped rare-earth garnets

Crystallization and stability of rare earth iron garnet/Pt/gadolinium gallium garnet heterostructures on Si

The crystallization of rare earth iron garnet films such as dysprosium iron garnet on Si substrates provides a path for integration of these complex oxides into magnetic devices. We report the growth of 50–75 nm thick dysprosium yttrium iron garnet (YDyIG) films, deposited without a seed layer then crystallized by a 750 °C rapid thermal anneal, forming a polycrystalline film with grains of several µm diameter containing radiating low-angle boundaries. The Y:Dy ratio affects the magnetization and anisotropy of YDyIG. Crystallization becomes more challenging as the garnet film thickness decreases. To crystallize thinner rare earth garnet films, tri-layer stacks consisting of a 50 nm thick gadolinium gallium garnet (GGG) seed layer, a 1.5 nm thick Pt diffusion barrier, and a 10 nm thick YDyIG film were prepared. The YDyIG/Pt/GGG tri-layers showed agglomeration of the Pt leading to a morphology consisting of a polycrystalline garnet film enriched with Dy and Fe and containing a layer of Pt nanoparticles embedded near its surface.

FARADAY EFFECT

This article describes a magneto-optical study of the faraday effect in rare-earth ferrite garnets. The Faraday effect is an odd magneto-optical effect in terms of magnetization, that is, the sign of the Faraday rotation depends on whether the direction of the light propagating in the crystal coincides with the direction of the magnetization vector M, or is antiparallel to the vector M. This circumstance underlies the well-known method of visual observation of magnetic domains in rare-earth ferrites - grenades.

Origin and dynamics of umbrella states in rare-earth iron garnets

Rare-earth iron garnets R3Fe5O12 are fascinating insulators with very diverse magnetic phases. Their strong potential in spintronic devices has encouraged a renewal of interest in the study of their low temperature spin structures and spin wave dynamics. A striking feature of rare-earth garnets with R-ions exhibiting strong crystal-field effects like Tb-, Dy-, Ho-, Er-, Tm- and Yb-ions is the observation of low-temperature non-collinear magnetic structures featuring “umbrella-like” arrangements of the rare-earth magnetic moments. In this study, we demonstrate that such umbrella magnetic states are naturally emerging from the crystal-field anisotropies of the rare-earth ions. By means of a general model endowed with only the necessary elements from the crystal structure, we show how umbrella-like spin structures can take place and calculate the canting-angle as a result of the competition between the exchange-interaction of the rare-earth and the iron ions as well as the crystal-field anisotropy. Our results are compared to experimental data, and a study of the polarised spin wave dynamics is presented. Our study improves the understanding of umbrella-like spin structures and paves the way for more complex spin wave calculations in rare-earth iron garnets with non-collinear magnetic phases.

Light and spins in rare-earth doped garnets

Spin-dependent optical properties of garnet crystals and garnet based ceramics, doped with cerium and also, along with cerium, co-doped with gadolinium and/or terbium, were studied by the method of optically detected of magnetic resonance by monitoring luminescence. The intensity of photoluminescence excited by circularly polarized light in the absorption bands of Ce3+ proved to be useful for selective monitoring of the population of the spin sublevels of the Ce3+ ground state. It was shown that due to cross-relaxation between the cerium and gadolinium electron spin systems the intensity of Ce3+ emission can be used to detect magnetic resonance of Gd3+. High-frequency EPR allowed finding a family of non-Kramers Tb3+ centers in yttrium aluminum garnet crystals. The influence of the magnetic resonance of Tb3+ on the luminescence of Ce3+ was observed. This suggests a coupling between the Tb3+ and Ce3+ systems, which are promising for coherent information processing. In irradiated crystals and ceramics of cerium-doped gadolinium-gallium garnet, magnetic field stimulation of the recombination of radiation defects was found, that is, it was shown that the energy accumulated during irradiation can be released in an external magnetic field. A huge increase in the afterglow intensity in a magnetic field and magnetic memory effects of magnetic memory were explained by the influence of strong internal magnetic fields on spin-dependent recombination.

Dielectric properties of (Y0.2Eu0.2Er0.2Dy0.2Lu0.2)3(AlxFe1-x)5O12 high-entropy garnet ceramics

A new kind of novel high-entropy rare earth garnet ceramics (HEREGCs, (Y0.2Eu0.2Er0.2Dy0.2Lu0.2)3(AlxFe1-x)5O12 (x = 0.4–0.6)) was designed and successfully synthesized by solid state reaction method. With the increase of Al content, the relative dielectric constant (εr′) at 100 Hz decreases from 4 × 104 to 1 × 102, while the dielectric loss (tanδ) increases from 0.93 to 2.65. The activation energy of grain boundary electrical conductivity (Egb) and grain electrical conductivity (Eg) are fitted according to Arrhenius’ law, which indicate that the increase of difference between Egb and Eg lead to the enhancement of dielectric properties. Our results provide the underlying insights needed to guide the study of colossal dielectric materials.

Antiferromagnetism and Ising ground states in the rare-earth garnet Nd3Ga5O12

In this paper, we investigate the low temperature magnetic properties of the rare-earth garnet compound Nd$_3$Ga$_5$O$_{12}$ in detail by means of magnetization, specific heat and magnetocaloric effect measurements. The magnetic thermal properties along with the crystal field calculations reveal that the Nd$^{3+}$ ions form into a frustrated hyper-kagome lattice with connected triangles have an Ising-like ground state with the easy axis along the local [100], [010] and [001] directions. Instead of a quantum spin liquid ground state, an antiferromagnetically ordered state is found below $T_{\mathrm{N}}=0.52~\rm K$. With applying field in the [111] direction, the antiferromagnetic order is suppressed at the critical field of $B_{\mathrm{c}}=0.75~\rm T$, and enhancement of the critical fluctuations with linear crossover behaviors is observed near the critical point.

Compositional screening of Ce-doped (Gd,Lu,Y)3(Al,Ga)5O12 ceramics prepared by quenching from melt and their luminescence properties

Quenching from the melt using an Optical Floating Zone furnace was investigated as a possible high-throughput preparation method in order to screen novel scintillating materials. To validate this method, polycrystalline rare-earth aluminum garnets and yttrium gallium aluminum garnets were synthesized and characterized by X-ray diffraction, photoluminescence and radioluminescence emission spectra as well as radioluminescence imaging and compared to the previously reported properties of those materials. In order to achieve rapid, but quantitative comparison of the materials, pellets fabricated from the synthesized powders were sintered; two different sintering conditions were investigated and compared. A simplistic energy deposition and light absorption model for brightness of opaque samples under X-ray irradiation was developed to estimate the relative scintillation efficiency of the materials. Based on the results, Y3Al5O12, LuY2Al5O12 and GdY2Al5O12 seem to have the highest scintillation efficiency among the prepared samples.

Inorganic Composites Luminophors in Lithium-Borate Glasses with Rare-Earth Elements for White-Emitting Diodes

The paper describes the synthesis of novel luminescent composite system, based on lithium-borate glass matrix with addition of rare-earth elements and yttrium-aluminum garnet finely divided powder. The new chemical composition of glass has been selected, composite’s fabrication technology was developed, the temperature conditions of glass and luminophore sintering as well. The spectral characteristics of the obtained luminescent composites are measured, and chromaticity diagrams are considered. The radiation spectra showed a maximum of about 560 nm, the maximum spectral intensity of the radiation is about 90 μw/cm2/nm. Powerful energy saving source of white light was produced.