Gadolinium Gallium Garnet Research Articles

Microwave magnon damping in YIG films at millikelvin temperatures

Magnon systems used in quantum devices require low damping if coherence is to be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG) has low magnon damping at room temperature and is a strong candidate to host microwave magnon excitations in future quantum devices. Monocrystalline YIG films are typically grown on gadolinium gallium garnet (GGG) substrates. In this work, comparative experiments made on YIG waveguides with and without GGG substrates indicate that the material plays a significant role in increasing the damping at low temperatures. Measurements reveal that damping due to temperature-peak processes is dominant above 1 K. Damping behavior that we show can be attributed to coupling to two-level fluctuators (TLFs) is observed below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK, linewidths of ∼1.4 MHz are achievable: lower than those measured at room temperature.

Spin transport in an insulating ferrimagnetic-antiferromagnetic-ferrimagnetic trilayer as a function of temperature

We present a study of the transport properties of thermally generated spin currents in an insulating ferrimagnetic-antiferromagnetic-ferrimagnetic trilayer over a wide range of temperature. Spin currents generated by the spin Seebeck effect (SSE) in a yttrium iron garnet (YIG) YIG/NiO/YIG trilayer on a gadolinium gallium garnet (GGG) substrate were detected using the inverse spin Hall effect (ISHE) in Pt. By studying samples with different NiO thicknesses, the spin diffusion length of NiO was determined to be ∼3.8 nm at room temperature. Surprisingly, a large increase of the SSE signal was observed below 30 K, and the field dependence of the signal closely follows a Brillouin function for an S=7/2 spin. The increase of the SSE signal at low temperatures could thus be associated with the paramagnetic SSE from the GGG substrate. Besides, a broad peak in the SSE response was observed around 100 K. These observations are important in understanding the generation and transport properties of spin currents through magnetic insulators and the role of a paramagnetic substrate in spin current generation.

Ultrathin interfacial layer with suppressed room temperature magnetization in magnesium aluminum ferrite thin films

Low-damping magnetic oxide thin films with small thicknesses are essential for efficient insulator spintronic devices, particularly those driven by spin torque effects. Here, we investigate the depth-resolved compositional and magnetic properties of epitaxial spinel MgAl0.5Fe1.5O4 (MAFO), which has recently been reported as a promising low-damping insulator. We find that ≈11 nm films exhibit optimal Gilbert damping, with a typical damping parameter of 0.001. While defects due to strain relaxation in the bulk of the film contribute to increased damping for large film thickness, the damping increase in thinner films is attributed to the presence of a chemically disordered magnetic dead layer at the film/substrate interface. This interfacial dead layer arises from an Fe-deficient MAFO layer. Notably, this layer is only about one-sixth the thickness of that found at the interface between yttrium iron garnet films and gadolinium gallium garnet substrates, making MAFO an ideal thin-film insulator for spin-torque applications.

Spin-wave diagnostics of the magnetization distribution over the thickness of a ferrite film

High-intensity microwave excitation of short-wavelength exchange spin waves in a normally magnetized epitaxial film of an yttrium iron garnet (YIG) has been found. The waves were excited in a thin diffusion layer at the boundary between the YIG film and a nonmagnetic gadolinium gallium garnet substrate. It propagates into the YIG film. In the pulsed excitation mode, a series of delayed echo pulses of the exchange waves reflected from the opposite surface of the film was observed. The distribution function of the magnetization over the thickness of the ferrite film was calculated based on the measurements of the time delay of the echo pulses. The dispersion characteristics of the detected waves were calculated.

Effect of a Substrate on the Magnetoelectric Effect in Rare-Earth-Doped Bismuth Iron Garnet

The mechanism of relaxation of the electric polarization in thin films of rare-earth-doped bismuth iron garnet on glass and gallium gadolinium garnet substrates is determined in magnetic fields of 0 and 12 kOe in the temperature range of 80–380 K. The change in the sign of the residual electric polarization after switching off the electric field and the magnetic-field-induced shift of the hysteresis loop in the applied magnetic field are found. Linear and quadratic magnetoelectric effects with the tensor components depending on the substrate type are observed. The linear magnetoelectric effect is related to the spin–orbit coupling of electrons at the film–substrate interface, whereas the quadratic one is determined by the exchange–striction mechanism.

The Magnetic Microstructure of YIG / GGG Films: Mossbauer Studies in the External Magnetic Fields

The Mossbauer studies of yttrium iron garnet (YIG) films grown on the gadolinium gallium garnet (GGG) substrate was realized for different films thickness (2.85 and 5.42 mm) at the applied external magnetic field. It is shown that the main changes in the magnetic microstructure of YIG/GGG films are occurred at magnetic field value up to 2.20 kOe. The changes of the hyperfine magnetic fields on the iron nuclei have been investigated and its isotropic component was analyzed. It was determined that the domain structure changes (in particular, the domains width enlarging) under the applied magnetic field increase with the film thickness decreasing.

Enhancing magneto-optical and structural properties of Bi-YIG thin film on glass substrate using poly[vinylpyrrolidone](PVP) assisted MOD method

A bismuth-substituted yttrium iron garnet (Bi-YIG) thin film on a glass substrate with high magneto-optical (MO) performance was fabricated using metal-organic decomposition (MOD). To enhance the MO performance of the as-grown Bi-YIG thin film, different amounts of polyvinylpyrrolidone (PVP) were introduced to a metal nitrate precursor solution as a reducing agent and growth modifier. By using the optimized concentration, we have obtained a Bi-YIG thin film that exhibited good morphology, high crystallinity, and high saturation magnetization. The Faraday rotation (FR) angle of this film reached its highest value of −8.0°/μm, which is close to that of thin films fabricated on gadolinium gallium garnet substrates (−10.5°/μm). Moreover, BixY3−xFe5O12 films with different Bi substitutions were synthesized; these films showed a higher FR angle, of up to −12.0°/μm (Bi2.5Y0.5Fe5O12), in which the peak position of the FR angle resided in the visible range (505–540 nm). This work reveals that high-quality Bi-YIG thin films on glass substrates via MOD are promising for MO device applications.

Morphology, Crystal Structure and Ferromagnetic Resonance Properties of Submicron-Thick Yttrium Iron Garnet Films Prepared by Pulsed Laser Deposition

Submicron-thick yttrium iron garnet films were grown on a gadolinium gallium garnet substrate by pulsed laser deposition. The morphology and crystal structure results show that the submicron-thick film has a flat surface, low surface roughness of ∼ 0.5 ± 0.05 nm and good epitaxy with the (444) plane. Magnetic hysteresis loops also indicate that the submicron-thick film has great soft magnetic properties. However, the ferromagnetic resonance (FMR) spectrum shows that the submicron-thick film has multiple resonance peaks. The angular dependence of the FMR response of the 10-nm-thick, 100-nm-thick and 525-nm-thick films shows that peaks 1 (at low field) and 2 (at high field) observed in the 525-nm-thick film spectrum originate from the internal layer and the outer layer of the films, respectively. Lastly, the angular dependence of the FMR linewidth shows that the lowest FMR linewidth occurred at an angle between the direction of the static field and film normal of 50°.

Effect of substrate defects on LIDT of (BiTm)3(GaFe)5O12 films grown by LPE

Recently, demands for magneto-optical (MO) materials with high laser-induced damage thresholds (LIDT) increased rapidly with the continuous development of high power lasers. In order to study the effect of substrate defects on LIDT of (BiTm)3(GaFe)5O12 films, in this study, (BiTm)3(GaFe)5O12 films without gadolinium gallium garnet (GGG) substrates and (BiTm)3(GaFe)5O12/GGG films were prepared by liquid-phase epitaxial (LPE) and mechanical lapping and polishing method. The optical and magneto-optical properties, crystal structure, LIDT and laser-induced damage morphologies of the prepared films were investigated. Experimental results pointed out that epitaxial (BiTm)3(GaFe)5O12 films have very high crystal and surface quality. A discontinuous defective layer with thickness of about 0–500 nm is located between GGG substrates and epitaxial films. Laser-induced damage tests and damage morphologies demonstrate that the discontinuous defective layers have an important effect on LIDT of epitaxial films, and LIDT of epitaxy films can be significantly improved by removing GGG substrates and discontinuous defective layers.

Growing of Thick Single-Crystalline La-Substituted Yttrium-Iron Garnet Films with Reproducible Parameters

Basic principles of growing the thick (35–60 мm) single-crystalline La-substituted yttrium-iron garnet (Y3−xLaxFe5O12, La :YIG) films with reproducible parameters have been formulated. La :YIG films are grown on gallium-gadolinium garnet (Gd3Ga5O12) substrates from a supercooled melt-solution (MS) consisting of Y2O3, La2O3, and Fe2O3 oxides and the PbO–B2O3 solvent. In order to minimize the implantation of Pb2+ ions into the films, which degrades the film quality, the epitaxy has to be performed at high temperatures and a low MS supercooling. It is found that, in order to maintain a constant growth rate of La :YIG films with reproducible parameters, a large MS mass (10–16 kg) has to be used, and the MS temperature has to be permanently lowered at a rate of 0.042 K/min.

Complement to “Optical and Judd‐Ofelt spectroscopic study of Er3+‐doped strontium gadolinium gallium garnet single‐crystal”

AbstractIn the previous paper “Optical and Judd‐Ofelt spectroscopic study of Er3+‐doped strontium gadolinium gallium garnet single‐crystal” (J Am Ceram Soc. 2019;102:873–878), we have reported optical and Judd‐Ofelt spectroscopic properties of Er3+‐doped strontium gadolinium gallate (SrGdGa3O7) single‐crystal, and the Judd‐Ofelt study was performed on the basis of unpolarized absorption spectrum of the crystal. Present work reports the corrected unpolarized absorption spectrum and Er3+ concentration in the crystal, and hence corrected Judd‐Ofelt spectroscopic properties and cross‐section data. In addition, the polarization effect was considered in the Judd‐Ofelt analysis on the basis of polarization‐resolved absorption spectra. Effective Judd‐Ofelt parameters are presented and discussed in comparison with the results from the unpolarized spectrum, and consistent results have been obtained. This study also considers the effects of some other factors on the Judd‐Ofelt parameters. These include Er3+ concentration and selection of Er3+ absorption bands for the Judd‐Ofelt analysis.

CuPt Alloy Thin Films for Application in Spin Thermoelectrics

Spin thermoelectrics represents a new paradigm of thermoelectricity that has a potential to overcome the fundamental limitation posed by the Wiedmann-Franz law on the efficiency of conventional thermoelectric devices. A typical spin thermoelectric device consists of a bilayer of a magnetic insulator and a high spin-orbit coupling (SOC) metal coated over a non-magnetic substrate. Pt is the most commonly used metal in spin thermoelectric devices due to its strong SOC. In this paper, we found that an alloy of Cu and Pt can perform much better than Pt in spin thermoelectric devices. A series of CuPt alloy films with different Pt concentrations were deposited on yttrium iron garnet (YIG) films coated gadolinium gallium garnet (GGG) substrate. Through spin Seebeck measurements, it was found that the Cu0.4Pt0.6/YIG/GGG device shows almost 3 times higher spin Seebeck voltage compared to Pt/YIG/GGG under identical conditions. The improved performance was attributed to the higher resistivity as well as enhanced spin hall angle of the CuPt layer.

The linear relationship of spin pumping energy in a La:YIG/Pt heterostructure used in a microwave rectifier

ABSTRACTLa3+ doped yttrium iron garnet films have been grown on (111) oriented gadolinium gallium garnet substrates via Liquid phase epitaxy technique as a basic material for ISHE device fabrication. Pt as a material with a large spin hall angle was used as a spin detection layer. We investigated the dependence of the spin pumping effect on the power and frequency of the excitation microwaves in La:YIG/Pt bilayers by measuring the ISHE voltage. We demonstrated that the area under the ISHE curve(SISHE) across a wide power range had a nearly linear correlation with the input microwave power (Pin). The parameter SISHE can be used to describe the spin current energy in a Pt layer which can be a useful parameter for a microwave rectifier.

A large magnetocaloric effect in two hybrid Gd-complexes: the synergy of inorganic and organic ligands towards excellent cryo-magnetic coolants

We report two hybrid Gd-complexes with the maximum entropy changes comparable to commercialized gadolinium gallium garnet Gd3Ga5O12 at a high field (7 T) and low fields (smaller than 3 T).

Tunable Ferromagnetic Strength in Niccolite Structural Heterometallic Formate Framework Based on Orthogonal Magnetic Orbital Interactions.

A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [AI][CrMII(HCO2)6] (AI = NH4H2OI and M = Mn for 1, AI = CH3NH3I and M = Fe for 2, AI = CH3NH2CH3I and M = Co for 3, AI = CH3NH3I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of CrIII (t2g3eg) and MII (t2g3eg2 for MnII, t2g4eg2 for FeII, t2g5eg2 for CoII, t2g6eg2 for NiII) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1-4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between CrIII and MnII ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (-Δ Smmax) up to 43.9 J kg-1 K-1 with Δ H = 7 T and T = 3.5 K, larger than most reported transition metal-based complexes and commercial gadolinium gallium garnet (Gd3Ga5O12) (-Δ Smmax = 38.4 J kg-1 K-1 with Δ H = 7 T). From 1, 2/3, to 4, an enhancement of the magnetic ordering temperature is observable due to the increasing strength of FO interactions between CrIII and MII ions. Our work provides a successful instance to modulate the strength of FO exchange via analyzing the orthogonal magnetic orbitals of heterometallic ions.

Fabrication of yttrium–iron–garnet/Pt multilayers for the longitudinal spin Seebeck effect

For longitudinal spin Seebeck effect (LSSE) devices, a multilayer structure comprising ferromagnetic and nonmagnetic layers is expected to improve their thermoelectric power. In this study, we developed a fabrication method for alternately stacked yttrium–iron–garnet (YIG)/Pt multilayer films on a gadolinium gallium garnet (GGG) (110) substrate, GGG/[YIG(49 nm)/Pt(4 nm)]n (n = 1–5) based on room-temperature sputtering and ex-situ post-annealing methods and we evaluated their structural and LSSE properties. The fabricated [YIG/Pt]n samples show flat YIG/Pt interfaces and almost identical saturation magnetization Ms although they contain polycrystalline YIG layers on Pt layers as well as single-crystalline YIG layers on GGG. In the samples, we observed clear LSSE signals and found that the LSSE thermoelectric power factor (PF) increases monotonically with increasing n; the PF of the [YIG/Pt]5 sample is enhanced by a factor of ∼28 compared to that of [YIG/Pt]1. This work may provide a guideline for developing future multilayer-based LSSE devices.

Surface acoustic waves in dynamic magnonic crystals for microwave signals processing

Surface acoustic waves (SAW) in dynamic magnonic crystals (DMC) are considered for their use to create tunable spin-wave gadgets for processing of microwave signals. To understand the principles of operation of the proposed gadgets, the necessary basic properties of DMC created by a SAW in the structure of “yttrium iron garnet film on a substrate of gallium gadolinium garnet” are given. The prototype of the unique nonreciprocal notch filter working in the range of 3600–4100 MHz at the biasing magnetic field of 640 Oe is fabricated and its main characteristics such as dependences of the frequency and the depth of rejection pits on the frequency and power of the controlling SAW are measured. At the frequency of SAW of 41 MHz and power of 30 mW, the depth of the rejection pit reached 23 dB, the tunable shift of the notch frequency equaled to 7 MHz for a frequency change of SAW by 1 MHz. DMC with SAW may also be used for frequency shifting and modulation of microwave signals. Two configurations of prototypes of frequency shifting devices have been suggested, fabricated and their workability was shown experimentally.

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface

We have clarified the origin of magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700{\deg}C onto gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG / GGG interface is demonstrated by means of composition depth profiling performed by X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and X-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and X-ray reflectometry studies of the YIG / GGG epitaxial system.

Optical and Judd‐Ofelt spectroscopic study of Er3+‐doped strontium gadolinium gallium garnet single‐crystal

AbstractEr3+‐doped strontium gadolinium gallium garnet (SrGdGa3O7) single‐crystal was grown by Czochralski method. The Er3+ concentration in the crystal was determined as 4.2 × 1021 ions/cm3 by inductively coupled plasma atomic absorption spectroscopy. Refractive index of the crystal was measured at the wavelengths of 633, 1311 and 1553 nm by prism coupling technique. The results show that the crystal is a positive uniaxial crystal with a birefringence of ~0.01, and the Sellmeier equation reported previously for the crystal doped with Nd3+ is also valid for the one doped with Er3+. Unpolarized absorption spectrum of the crystal was measured at room temperature and the Er3+ absorption cross‐section spectrum was calibrated from it. The Er3+ spectroscopic properties were studied by Judd‐Ofelt theory. Some fundamental spectroscopic parameters were obtained that include absorption coefficient and cross‐section spectral distributions, electronic transition oscillator strength, Judd‐Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency.