GGG Substrates Research Articles

Microstructured growth by liquid phase epitaxy of scintillating Gd3Ga5O12 (GGG) doped with Eu3+

Microstructuration is useful for improving, tuning, or altering material properties and is used in various fields. It is applied to scintillating screens to enhance light extraction and to combine a high X-ray absorption efficiency of the scintillator with a good spatial resolution of the image. Even though the concept of microstructured scintillators is promising, only a few options have been explored and reported, leaving room for advancement. Here, we present the procedure for growing microstructured GGG:Eu with liquid phase epitaxy onto laser-treated GGG substrates with crystallographic orientations (100) and (111). It was found that the microstructure grows epitaxially on the substrate, maintaining the orientation and that its crystallinity is good and comparable to normal epitaxial films of GGG:Eu. The optical properties were also investigated thoroughly and are comparable to the un-structured epitaxial GGG:Eu films. We believe that these promising results can pave the way for other materials to be grown in a microstructured manner, which can be valuable also outside of scintillation for various fields.

Temperature controlled magnon–photon coupling in a YIG/GGG-superconducting cavity coupled system

To explore potential applications in classical and quantum information transfer, the hybrid systems between yttrium iron garnet (YIG) and cavities have been extensively studied, and four coupling regimes have been defined based on the relative strength between the coupling strength and dissipation rate of each subsystem. Achieving the control of magnon–photon coupling between nano-thick YIG films and cavities remains to be explored. We experimentally measure the microwave transmission spectra of a nano-thick yttrium iron garnet/gadolinium gallium garnet (YIG/GGG) film coupled to a superconducting cavity at different temperatures. The dissipation rate of the superconducting cavity increases significantly with decreasing temperature, which is influenced by the temperature-dependent magnetic susceptibility of the GGG substrate. Accompanied by the temperature-dependent magnon dissipation rate, a continuous transformation of the coupled system in strong coupling, Purcell and weak coupling regimes is achieved.

Interfacial layer effect on the enhancement of gilbert damping in RF magnetron sputtered Y3Fe5O12/Gd3Ga5O12 thin films

We report the magnetization dynamics study in Y3Fe5O12 (YIG) film grown by rf magnetron sputtering techniques. The growth-induced interfacial layer is believed to affect the top YIG layer, interrupting the magnetic properties associated with it drastically. The structural data confirmed the epitaxial and strained growth of YIG on a highly matched GGG (100) substrate. The frequency variation of the FMR signal yields various important parameters, such as the line width (ΔH), effective magnetization (4πMeff), and damping constant (α) at 300 K. The significant increase in 4πMeff to 2187.848 Oe reflects the presence of non-collinear or antiparallel arrangement of magnetic moment in YIG thin-film. Apart from this value of α was reported to be 1.5 × 10−3 which is substantially higher than the values reported in the literature for such higher-quality epitaxial thin films. We anticipate that a detailed analysis of these findings will provide excellent speculation in the field of magnonics, advanced spintronics and terahertz frequency-related applications.

Effect of annealing temperature on the properties of BaFe12O19 thin films deposited on GGG (1 1 1) substrates by pulsed laser deposition

In this work, BaFe12O19 thin films with perpendicular magnetic anisotropy have been deposited on GGG (111) substrates by pulsed laser deposition in an oxygen atmosphere using a KrF excimer laser. The effects of annealing temperature on the microstructural, magnetic, and microwave properties of BaFe12O19 thin films were investigated. It is found that the properties of BaFe12O19 films are very sensitive to the annealing temperature, and excellent films are obtained when the annealing temperature is above 900 °C. X-ray diffraction diagrams show that films annealed at higher temperatures (≥950 °C) have better crystallization and higher perpendicular orientation. Atomic force images show the surface morphology of annealed films above 900 °C to be very smooth, with a minimum roughness of 0.754 nm. Hysteresis loops reveal that the saturation magnetization of the films annealed above 1000 °C is similar to that of bulk barium ferrite, and the maximum value of 4676 Gs is obtained at 1100 ℃. The anisotropy field increases with the increase in annealing temperature, reaching a maximum of 18.0 kOe at 1050 °C. The remanence ratio and saturation magnetization also show an upward trend as the annealing temperature rises. The film annealed at 1100 °C shows a very narrow ferromagnetic resonance linewidth with a width of about 256 Oe at 39 GHz. And the ferromagnetic resonance linewidth of the films decreases as the temperature rises, which means that films annealed at higher temperatures have less microwave loss.

Spin Hall magnetoresistance and the effect of post-annealing temperature in the MOD-grown HoIG

We present the fabrication of ultrathin Ho3Fe5O12 (HoIG) films on 111- oriented-Gd3Ga5O12 (GGG) via the metal-organic decomposition (MOD) method followed by a sequence annealing process. We characterized the crystal structure, surface morphology, and magnetic properties to study the effect of annealing temperature on the quality of MOD-grown HoIG films. For temperatures higher than 800 ⁰C, we observe the infiltration of Iron (Fe) from the HoIG film into the GGG substrate. In particular, the Fe-diffusion is significantly enhanced for a 1000 ⁰C-annealed sample of which crystal structure and magnetic properties are also affected. For temperatures lower than 800 ⁰C, on the other hand, the smooth surface and strong crystallinity cannot be guaranteed. This suggests that an annealing temperature of 800 ⁰C is the optimal condition for the MOD-grown HoIG film. The quality of the sample is further confirmed by measuring the spin Hall magnetoresistance (SMR) of HoIG/Pt, in which we found the unconventional angular dependence and comparable spin mixing conductance similar to the previous reports in other single crystalline IGs.

Strain-modulated spin Hall magnetoresistance in YIG/Pt heterojunctions

This paper reports that the substrate-induced strain effect can be utilized to control spin Hall magnetoresistance (SMR) of YIG/Pt heterojunctions. The YIG films with in-plane compressive strain and tensile strain are respectively prepared on GGG and GSGG substrates by pulsed-laser deposition. The ratio of SMR of YIG/Pt heterojunctions with YIG under the in-plane tensile strain state is 1.6 time larger than that of YIG with the out-of-plane compressive strain state. The spin mixing conductance of YIG/Pt interface increases with the substrate-induced in-plane tensile strain on YIG. The increase of roughness and the reduction of ratio of Fe3+/Fe2+ for YIG surface is responsible for this modulation. This finding provides an interesting prospect for control of SMR by substrate-induced strain effect.

Optimizing the quality of epitaxial Y3Fe5O12 thin films via a two-step post-annealing process

Background: Yttrium iron garnet (Y3Fe5O12, YIG) is a prototype magnetic garnet, which possesses the lowest magnetic damping (α) value so far on the earth among all discovered or synthesized materials. This makes it the best candidate for categories of next generation spintronic devices, possessing great application potentials. Methods: A two-step annealing method, with first annealing carried out at a relative low temperature and second annealing at a relatively higher temperature, had been used for the first time to crystallize room temperature sputtered amorphous Y3Fe5O12 (YIG) films on Gd3Ga5O12 (GGG) substrates. The crystalline structure, surface morphology, static and dynamic magnetic properties of the obtained YIG films were characterized through X-ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) systems, respectively. Results: It was found that the YIG films obtained via this elaborate annealing method, have a much smoother surface, lower coercivity field, and better dynamic magnetic properties, than that of the YIG films annealed by ordinary one-step approach. Particularly, the ferromagnetic resonance (FMR) linewidth of the best two-step annealed 25 nm YIG film is lower than ~7 Oe at frequency of 10 GHz. Conclusions: Our work clarifies that this two-step annealing approach can effectively improve the quality of the obtained epitaxial YIG films on GGG substrates.

Magneto-optical property and magnetic anisotropy of (100) oriented R0.5Bi2.5Fe5O12 (R = Eu, Sm, and Pr) thin films prepared by metal–organic decomposition

Bi-substituted rare-earth iron garnets, R3−xBixFe5O12 (Bi:RIG), where R represents one of the rare-earth elements, exhibit the excellent magneto-optical (MO) properties that increase with Bi content x. In addition, magnetic properties of Bi:RIGs, such as the magnetization, the magnetic anisotropy, and the magnetostriction, could be controlled by choosing rare-earth elements. In this paper, we report on R0.5Bi2.5Fe5O12 (Bi2.5:RIG, R = Pr, Sm, and Eu) thin films on Gd3Ga5O12 (GGG) (100) single crystal substrates prepared by the metal–organic decomposition method. XRD analysis reveals that Bi2.5:RIG thin films are grown along the same orientation with GGG substrates, and their lattice constants are dependent on the ionic radii of the rare-earth ions. MO measurements show that Faraday spectra of the Bi2.5:RIG thin films have a typical spectral structure observed for Bi:RIGs. The magnetic anisotropy constants, the uniaxial magnetic anisotropy energy Ku, and the magnetocrystalline anisotropy energy K1 of Bi2.5:RIG (R = Y, Pr, Nd, Sm, and Eu) thin films are investigated by using the ferromagnetic resonance measurement.

Reproducible low Gilbert damping yttrium iron garnet by magnetron sputtering

Reproducible growth of single-crystalline (111) yttrium iron garnet (YIG) with very low Gilbert damping (α) has been reported by the use of several techniques, and continues to attract the attention of many groups in sprintronics and magnonics. We report on the growth of YIG thin films onto GGG (111) substrates by magnetron sputtering, followed by an ex-situ oxygen flow heat treatment. The magnetic properties were studied by ferromagnetic resonance, and the structural and morphological properties by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. The annealing parameters and thickness dependency on the magnetic properties was systematically investigated. A decrease in α for almost ten times was found preventing the YIG growth at the edges of the substrate by the use of lithography. For YIG 60 nm thick α were measured as (1.72 ± 0.08) × 10−4, Ms = 179 ± 2 emu cm−3, and surface roughness as 0.23 nm. To quantify the growth as being of good quality, we measured the spin current injection via spin pumping to an adjacent bismuth-doped copper layer with spin mixing conductance g↑↓ = 2.16 × 1018 m−2, for a platinum layer g↑↓ = 2.17 × 1018 m−2, with the detection of a 7 μV in the inverse spin Hall effect voltage, quantities which are in good agreement with the best values reported so far.

Evaluation of the magnetization dynamics in various thick YIG films using our proposed measurement technique

This paper describes the evaluation of magnetization dynamics in YIG polycrystalline films with various thicknesses using our proposed measurement technique. The saturation magnetostriction (λs) are approximately less than −1.0×10−6 regardless of the film thickness and are lower than that of bulk polycrystalline YIG, which might be attributed to the structural and/or magnetic inhomogeneities. On the other hand, the in-plane effective damping constant (αeff) decreases approximately from 0.00384±0.00029 to 0.00316±0.00013 with the increase of film thickness, and their values are much higher than those of nano-meter thick and micro-meter thick YIG films deposited on GGG substrates. The reason for this difference may be that the extrinsic damping originating from the magnetic inhomogeneities are enhanced in the film plane. In addition, αeff slightly increases as λs decreases. This tendency is opposite to those of Ni-Fe and Fe-Si polycrystalline films, and the correlation between αeff and λs does not appear. Therefore, these results suggest that magnetic inhomogeneities are mainly influenced to both αeff and λs in the film plane.

Deposition of Crystalline GdIG Samples Using Metal Organic Decomposition Method

Fabrication of high quality ferrimagnetic insulators is an essential step for ultrafast magnonics, which utilizes antiferromagnetic exchange of the ferrimagnetic materials. In this work, we deposit high-quality GdIG thin films on a (111)-oriented GGG substrate using the Metal Organic Decomposition (MOD) method, a simple and high throughput method for depositing thin film materials. We postannealed samples at various temperatures and examined the effect on structural properties such as crystallinity and surface morphology. We found a transition in the growth mode that radically changes the morphology of the film as a function of annealing temperature and obtained an optimal annealing temperature for a uniform thin film with high crystallinity. Optimized GdIG has a high potential for spin wave applications with a low damping parameter in the order of 10−3, which persists down to cryogenic temperatures.

Identification of a new source of magnon relaxation in interface between epitaxial iron garnet ferrite films and GGG substrate

We have investigated the intermediate layer between the gallium-gadolinium garnet substrate and the yttrium-iron garnet epitaxial film. This interlayer is characterized by a large magnetic moment at low temperatures, which leads to an anomalous dependence of the susceptibility and a shift in the magnetic resonance frequency upon cooling. This shift is much larger than might be expected due to magnetization anisotropy, substrate paramagnetic ions, and magnetostriction. We found that this interlayer plays a major role in magnetic relaxation processes in the temperature range below 50 K.

Effect of oxygen growth-pressure on microstructural and magnetic properties of pulse laser deposited epitaxial YIG thin films

We investigated the effect of oxygen growth-pressure on the structural and magnetic properties of epitaxial YIG thin films. YIG films were grown on single crystalline GGG substrates with (111) orientations by pulse laser deposition technique. In-situ oxygen-gas pressure variations in the range of 0.0025–0.15 mbar was adopted to demonstrate the perfect growth. Structural analysis confirmed that the films were single crystalline in nature. Atomic force microscopy analysis indicated that roughness of the films decreases with increase of oxygen pressure. Saturation magnetization was enhanced by a factor of 17% over increase of oxygen pressure. Through angular dependent ferromagnetic resonance (FMR) measurements along film’s in-plane (φ-variation) and out-of-plane (θ-variation) geometries, resonance fields [HrθH,φH] and FMR linewidths [∆HrθH,φH] were obtained. Using theoretical analysis important material parameters such as; saturation magnetization, gyromagnetic ratio, uniaxial anisotropy, cubic anisotropy and Gilbert damping were evaluated. We have obtained lowest Gilbert damping ~4.37×10−5 for 0.15 mbar oxygen pressure deposited YIG film.

Growth of homogeneous-phase YIG grains on Si substrates and their optical properties on a micron scale

Growing homogeneous-phase YIG grains on Si substrates through a low-cost sol-gel route is crucial to the integration of patterned YIG on a Si-based photonic platform. Here, the fabrications of both YIG powders and films are compared for studying their difference in phase transition. A buffered layer of YIP is found necessary for the complete conversion of Y2Fe4O9 phase to YIG phase on Si substrates. Through the optimization of experimental factors, homogeneous-phase YIG grains with micron-scale size and rectangle profile are fabricated on the Si substrate. The narrow and strong Micro-Raman peaks of the as-grown grain reveal the crystal lattice with high perfection while slight shifts of some Raman peaks indicate the residual stress induced by repeated annealing. The magneto-optical property of the YIG grain, characterized on a micron scale by using a home-made system, is found comparable to that of the commercially epitaxial YIG film on a GGG substrate.

Preparation and orientation mechanism analysis of (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> magneto-optical single crystal film with out-of-plane orientation

Liquid-phase epitaxy (LPE) is one of the best techniques for the preparation of single crystal garnet films. However, the specific Faraday rotation angle of Yttrium iron garnet (YIG) is small, and its easy magnetization axis is parallel to the film surface. The YIG requires a large external saturation field, which cannot meet the development needs of magneto-optical devices. It is found that Bi-substituted YIG(Bi:YIG) film has a larger specific Faraday angle. By adjusting the easy magnetization axis of Bi: YIG perpendicular to the film surface, the saturation magnetization of Bi: YIG can be reduced, so that it can work under a small external magnetic field. This meets the development needs of miniaturization and energy saving of magneto-optical device. The saturation magnetization of garnet film can be effectively reduced by substituting Ga<sup>3+</sup> for YIG crystal, mainly for Fe<sup>3+</sup> at the 24d position of its tetrahedron. And the lattice constants of Gd<sub>3</sub>Ga<sub>5</sub>O<sub>12</sub> (GGG) and YIG are 1.2383 nm and 1.2376 nm, respectively. However, the radius of Bi<sup>3+</sup> (10.8 nm) is larger than that of Y<sup>3+</sup> (9.0 nm), the lattice mismatch of garnet film increases with the incorporation of Bi<sup>3+</sup>. In order to neutralize the lattice expansion caused by Bi<sup>3+</sup>, Tm<sup>3+</sup> (8.69 nm) with a radius smaller than that of Y<sup>3+</sup> (9.0 nm) is selected. Based on the theoretical analysis of the magnetocrystalline anisotropy of garnet film, (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> mono-crystalline films with different growth temperatures and different thickness values are grown by LPE on GGG (111) substrates. The experimental results show that when the thickness of epitaxial film is greater than 1 μm, the influence of shape anisotropy on magnetocrystalline anisotropy can be ignored. With the increase of growth temperature, the substitution number of Bi<sup>3+</sup> ions decreases gradually, the lattice constant of epitaxial film decreases gradually, and the lattice mismatch first decreases and then increases. Then, the state of compressive stress gradually changes into that of tensile stress. Compared with growth-induced anisotropy, the stress-induced anisotropy is dominant in the change of magnetocrystalline anisotropy. The Verdet constant of (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> film is 11.8 × 10<sup>4</sup> rad/Tm@1064 nm. The results show that the prepared (BiTm)<sub>3</sub>(GaFe)<sub>5</sub>O<sub>12</sub> mono-crystalline films have great development potential in magneto-optical devices.

Magnetization coupling in a YIG/GGG structure

We studied the magnetization coupling between an yttrium-iron-garnet (YIG) film and a gadolinium-gallium-garnet (GGG) substrate at low temperature using magnetic resonance measurements. We observed both acoustic and optical mode hybridization between the magnetization of the 3-$\ensuremath{\mu}\text{m-thick}$ YIG film, ${M}_{\mathrm{YIG}}$, and the magnetization of the GGG substrate, ${M}_{\mathrm{GGG}}$, corresponding to in-phase and out-of-phase coupling, respectively. This experimental observation can be described by an antiferromagnetic-type interaction between ${M}_{\mathrm{YIG}}$ and ${M}_{\mathrm{GGG}}$ in the Landau-Lifshitz-Gilbert equation. Taking this approach we find that the effective field induced by magnetization coupling can be enhanced by decreasing the temperature or increasing the external field, providing a means to control magnon dynamics in YIG for magnonic device applications.

Sensitivity and Noise of a Magnetic Field Sensor Based on Magnetostatic Spin Wave YIG Device and Its Integrated Electronics

Since few decades, research in the magnonic area, which studies the phenomenon of spin waves propagation in magnetic materials, has grown simultaneously with the emergence of the so-called spintronic and nano-structured magnetic materials. Recent works exposed the interest of such devices for designing magnetic field sensors, considering the dependence of the transmission parameter S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> regarding the external applied magnetic field, for excitation frequency of several GHz. In this paper, we have investigated the ability of spin wave propagation phenomenon to be used as a magnetometer by characterizing its expected performances, particularly the output sensitivity, expressed in unit of V/T. The sensing element is designed from a YIG film (10 mm x 5 mm x 19.4 μm) deposited on GGG substrate. It is placed on a microstrip antenna transducer made of two copper lines, respectivelyto excite and measure the spin waves. The excitation is provided by a sine electromagnetic wave at a fixed frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1.146GHz. The induced spin waves propagate along the main length direction of the YIG material and induce a voltage signal at the output antenna at the carrier frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . When the external DC magnetic field varies, it yields a modulated signal. The dedicated and reduced electronic conditioning circuitry, based on a I/Q quadrature demodulator, allows to extract the field variations information with an output sensitivity of about 20V/T. Considering that the dominating noise sources are those due to the electronic conditioning circuitry, a sensor equivalent magnetic noise √ level of several nT/ Hz in white noise region was obtained.

Magnetoimpedance of Epitaxial Y3Fe5O12 (001) Thin Film in Low-Frequency Regime

The atomically flat interface of the Y3Fe5O12 (YIG) thin film and the Gd3Ga5O12 (GGG) substrate plays a vital role in obtaining the magnetization dynamics of YIG below and above the anisotropy field. Here, magnetoimpedance (MI) is used to investigate the magnetization dynamics in fully epitaxial 45 nm YIG thin films grown on the GGG (001) substrates using a copper strip coil in the MHz-GHz frequency region. The resistance (R) and reactance (X), which are components of impedance (Z), allow us to probe the absorptive and dispersive components of the dynamic permeability, whereas a conventional spectrometer only measures the field derivative of the power absorbed. The distinct excitation modes arising from the resonance in the uniform and dragged magnetization states of YIG are respectively observed above and below the anisotropy field. The magnetodynamics clearly shows the visible dichotomy between two resonant fields below and above the anisotropy field and its motion as a function of the direction of the applied magnetic field. A low value of a damping factor of ∼4.7 - 6.1 × 10-4 is estimated for uniform excitation mode with an anisotropy field of 65 ± 2 Oe. Investigation of below and above anisotropy field-dependent magnetodynamics in the low-frequency mode can be useful in designing the YIG-based resonators, oscillators, filters, and magnonic devices.

Spin excitations in laser-molecular-beam epitaxy-grown nanosized YIG films: towards low relaxation and desirable magnetization profile

We describe the synthesis of nanosized Y3Fe5O12 (YIG) films grown by laser-molecular-beam epitaxy on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NdGG) substrates with (111) orientation and present the results of ferromagnetic resonance (FMR) and spin-wave propagation studies in these heterostructures. It is found that the magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin-wave propagation experiments. For YIG/NdGG and YIG/GGG structures, the FMR linewidth ΔH of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ΔH is explained by typical relaxation processes caused by the presence of Fe2 + ions. From the spin-wave propagation study, it is also found that the relaxation of spin-waves explains only a minor part of the FMR single-peak linewidth in YIG/NdGG structures. On the basis of the obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed.

Magnetization switching induced by magnetic field and electric current in perpendicular TbIG/Pt bilayers

Magnetic insulators (MIs) have attracted great attention because of their low Gilbert damping, long spin transmission length, and no Ohmic loss. In this study, the high quality TbIG films with perpendicular magnetic anisotropy were epitaxially grown on GGG (111) substrates. In TbIG/Pt bilayers, the angular dependence of coercivity is found to obey the Kondorsky model, suggesting the magnetization reversal mechanism of magnetic domain nucleation and expansion. The transverse component of spin Hall magnetoresistance (SMR), which is analogous to the planar Hall resistance in a ferromagnetic metal, is found to be about seven times larger than the SMR-induced anomalous Hall resistance (analogous to the anomalous Hall resistance in a ferromagnetic metal). Moreover, the phase diagrams of the current-induced magnetization switching with different angles and magnitudes of the assisting magnetic field were drawn for the TbIG/Pt bilayers. The current-induced damping-like effective field (HDL) characterized by the harmonic measurements was evaluated to be about 164 Oe/108 A cm−2. By providing a comprehensive investigation of magnetization switching behaviors in MIs, our results will promote the application of ultralow-dissipation MI based spintronic devices.