Gadolinium Gallium Garnet Substrates Research Articles

An edge-coupled magnetostatic bandpass filter

The further development of 5G and 6G communication systems introduced new frequency allocations beyond 6 GHz, necessitating the development of compact bandpass filters that can operate over wide gigahertz frequency ranges. Herein, we report on the design, fabrication, and characterization of an edge-coupled magnetostatic forward volume wave bandpass filter (MSFVW). Using micromachining techniques, we fabricate both 2-pole and 4-pole filters from a yttrium iron garnet (YIG) film grown on a gadolinium gallium garnet (GGG) substrate with inductive transducers. By adjusting an out-of-plane magnetic field, we demonstrate linear center frequency tuning for a 4th-order filter from 4.5 GHz to 10.1 GHz while retaining a fractional bandwidth of 0.3%, an insertion loss of 6.94 dB, and a − 35 dB rejection level. We characterize the filter nonlinearity in the passband and stopband with IIP3 measurements of − 4.85 dBm and 25.84 dBm, respectively. In this work, we demonstrate a compact octave tunable narrowband channel-select filter with a significant degree of design flexibility and performance comparable to the state-of-the-art.

Nanometer-thick Ga/Al substituted yttrium iron garnet ultra-thin films by liquid phase epitaxial method

Abstract In microwave and spintronic applications, the Gilbert damping coefficient and ferromagnetic resonance (FMR) line width play a decisive role in the component losses. Yttrium iron garnet (YIG) film is a good candidate due to the extremely small damping factor. 4.8 and 51.3 nm ultra-thin Y3(GaAlFe)5O12 (GaAl-YIG) films are grown on gadolinium gallium garnet (GGG) substrate using liquid phase epitaxial (LPE) technology. The films show a (111) orientation and tensile strain, and the roughness of the film surface is small. The films show a low saturation magnetization because of Ga and Al substituted, and the comparison of magnetization properties with film thickness is analyzed. The FMR line width is tested, and the calculated damping constant of the 51.3 nm film is on the order of 10−4. The structural and magnetization properties analysis demonstrates that LPE technology has the potential to provide nanometer-thick garnet films for low-loss spintronic devices.

Enhancing terahertz magneto-optical effects in wafer-scale RIG single crystal thick films with anti-reflective coatings for improved transmittance

Wafer-scale rare-earth iron garnet (RIG) single crystal thick films were fabricated on 3-in. gadolinium gallium garnet (GGG) substrates using liquid phase epitaxy. The terahertz transmittance of the RIG crystals improved after removing the GGG substrate by polishing. The time-domain spectra at Terahertz (THz) frequencies indicate the existence of a magneto-optical effect in RIG samples. The results indicate that the RIG samples exhibit a high refractive index of ∼4.50 within the 0.1–1.0 THz frequency range, a transmittance of around 40%, and an absorption rate of only 10–50 cm−1. The Faraday rotation angles of the thick single-crystal films of the RIG samples were measured using a THz-TDS system. The RIG has a thickness of ∼330 μm. The Faraday rotation angles of RIG crystals at THz frequencies can reach up to 16° when an external magnetic field of 0.18 T is applied. The Verdet constants of the RIG sample were calculated to be ∼120°/mm/T. To improve the transmittance of the RIG sample, epoxy resin and polymethylpentene (TPX) were used as anti-reflective films. The transmittance of the RIG sample increased by ∼5% for the 80 μm thick epoxy and about 10% for the 320 μm thick TPX. Therefore, this RIG single crystal thick film can achieve a low loss, a high transmittance, and a strong magneto-optical effect in the terahertz region with the cooperation of a reflection-reducing film. It is expected to have wide applications in terahertz magnetic polarization conversion, non-reciprocal phase shifters, and isolators.

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 μm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

Large-scale fabrication of thulium iron garnet film with perpendicular magnetic anisotropy using RF magnetron sputtering

Large-scale fabrication of thulium iron garnet (TmIG) films on gadolinium gallium garnet (GGG) substrates, with a total area of 25 cm2, has been demonstrated by rotating substrate holders during on-axis sputtering. By optimizing the growth parameters based on the pressure and flow rate of the oxygen ratio, a Tm/Fe ratio of 0.65 was obtained, which is close to the stoichiometry of TmIG. The increase in post-annealing temperature has induced the growth of the TmIG structure by the strain of the lattice constant mechanism. At the highest post-annealing temperature, the crystal structure of TmIG (444) and the perpendicular magnetic anisotropy (PMA) were obtained. This result demonstrates the potential method for large-scale fabrication of TmIG film with PMA.

In-plane magnetic properties and anisotropy of scandium substituted thulium iron garnet thin films for fluxgate magnetometer

In-plane easily magnetized scandium substituted thulium iron garnet films(Tm3Fe5-xScxO12) with soft magnetic properties have recently attracted attention for fluxgate magnetometer applications. In this paper, thin Tm3Fe5-xScxO12 films were prepared on gadolinium gallium garnet substrates by liquid phase epitaxial(LPE) method. Microstructural properties, composition, magnetic properties and the in-plane anisotropy of the films were discussed. We found that the films turned from tensile stress to compressive stress as the Sc3+ substitution decreased, and the in-plane anisotropy was mainly caused by stress reducing as Sc3+ declined. By analyzing the in-plane magnetic hysteresis loops, the magnetic performance was the best when x = 0.75. Tm3Fe4.25Sc0.75O12 film had the lowest in-plane coercive field(0.006 Oe) and the highest initial magnetic permeability(378), which was more beneficial to realize fluxgate magnetometers.

Patterning Magnonic Structures via Laser Induced Crystallization of Yittrium Iron Garnet

AbstractThe fabrication and integration of high‐quality structures of Yttrium Iron Garnet (YIG) is critical for magnonics. Films with excellent properties are obtained only on single crystal Gadolinium Gallium Garnet (GGG) substrates using high‐temperature processes. The subsequent realization of magnonic structures via lithography and etching is not straightforward as it requires a tight control of the edge roughness, to avoid magnon scattering, and planarization in case of multilayer devices. In this work a different approach is described based on local laser annealing of amorphous YIG films, avoiding the need for subjecting the entire sample to high thermal budgets and for physical etching. Starting from amorphous and paramagnetic YIG films grown by pulsed laser deposition at room temperature on GGG, a 405 nm laser is used for patterning arbitrary shaped ferrimagnetic structures by local crystallization. In thick films (160 nm) the laser induced surface corrugation prevents the propagation of spin‐wave modes in patterned conduits. For thinner films (80 nm) coherent propagation is observed in 1.2 µm wide conduits displaying an attenuation length of 5 µm that is compatible with a damping coefficient of ≈5 × 10−3. Possible routes to achieve damping coefficients compatible with state‐of‐the art epitaxial YIG films are discussed.

Damping and Interfacial Dzyaloshinskii-Moriya Interaction in Thulium Iron Garnet/Bismuth-Substituted Yttrium Iron Garnet Bilayers.

Thin films of ferrimagnetic iron garnets can exhibit useful magnetic properties, including perpendicular magnetic anisotropy (PMA) and high domain wall velocities. In particular, bismuth-substituted yttrium iron garnet (BiYIG) films grown on garnet substrates have a low Gilbert damping but zero Dzyaloshinskii-Moriya interaction (DMI), whereas thulium iron garnet (TmIG) films have higher damping but a nonzero DMI. We report the damping and DMI of thulium-substituted BiYIG (BiYTmIG) and TmIG|BiYIG bilayer thin films deposited on (111) substituted gadolinium gallium garnet and neodymium gallium garnet (NGG) substrates. The films are epitaxial and exhibit PMA. BiYIG|TmIG bilayers have a damping value that is an order of magnitude lower than that of TmIG, and BiYIG|TmIG|NGG have DMI of 0.0145 ± 0.0011 mJ/m2, similar to that of TmIG|NGG. The bilayer therefore provides a combination of DMI and moderate damping, useful for the development of high-speed spin orbit torque-driven devices.

Enhanced terahertz magneto-optical performance in substrate-free ultra-thick TbErBi:RIG crystal films

A wafer-scale single crystal thick film of rare-earth iron garnet (RIG) has been successfully produced on a 3-in. gadolinium gallium garnet (GGG) substrate using the liquid phase epitaxy method. The RIG crystal's thickness measures ∼550 μm. By removing the GGG substrate through polishing, we improved the terahertz (THz) transmittance of the RIG crystal. In the frequency range of 0.1–1.0 THz, the RIG material exhibits a large refractive index of around 4.50, with a transmittance of ∼60% and an absorption rate of only 10–50 cm−1. Furthermore, we investigated the THz magneto-optical effect in the RIG material through THz time-domain spectroscopy. The observed results demonstrate the presence and significance of the magneto-optical effect in the RIG crystal. To provide further insights, we measured the THz Faraday rotation angle of the 550 μm-thick RIG crystal using the THz-TDS system under an external magnetic field of 0.17 T. The measured Faraday rotation angle reached 22°, and the calculated Verdet constant for the RIG sample was ∼120°/mm/T. Considering these findings, our study highlights the unique properties of this wafer-scale single crystal thick film of RIG, including its low loss, high transmission, and strong magneto-optical effect in the THz range. These characteristics make it a promising candidate for various applications, such as THz magnetic polarization conversion, non-reciprocal phase shifters, and isolators.

Optical and magneto‐optical properties of pulsed laser‐deposited thulium iron garnet thin films

AbstractThis work presents a combined optical and magneto‐optical spectroscopic study of thulium iron garnet (Tm3Fe5O12, TmIG) films on substituted gadolinium gallium garnet (Gd2.6Ca0.4Ga4.1Mg0.25Zr0.65O12, sGGG) substrates. Spectroscopic ellipsometry, transmission spectroscopy, magneto‐optical Kerr effect spectroscopy and Raman spectroscopy results are presented for TmIG films with a thickness in the range from 20 to 300 nm grown on sGGG by pulsed laser deposition. The complex dielectric functions of TmIG and sGGG are determined and compared with previously published results for bulk yttrium iron garnet and GGG, respectively. The magneto‐optical spectroscopy corroborated with Raman spectroscopy sheds light on strain‐induced changes as a function of TmIG film thickness.

Micromachined Tunable Magnetostatic Forward Volume Wave Bandstop Filter

We have successfully designed, fabricated, and characterized a planar monolithic yttrium iron garnet (YIG) Chebyshev bandstop filter on gadolinium gallium garnet (GGG) substrate with tunable frequency, low insertion loss (IL), and high rejection. This filter is created in YIG micromachining technology that allows direct placement of metal transducers on YIG for strong spin-wave coupling. With an out-of-plane 3900-Oe bias field, the bandstop filter exhibits 55-dB maximum stopband rejection at a center frequency of 6 GHz, with 2-dB passband IL and 37.8-dBm passband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ \mathrm{IIP_3} $</tex-math> </inline-formula> . By applying different bias fields, the stopband center frequency is tuned from 4 to 8 GHz while maintaining more than 30-dB rejection. Incorporated with proper design of tunable compact electromagnet, this new filter design can provide attenuation of spurs appearing across the fifth generation (5G) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$</tex-math> </inline-formula> -band spectrum.

Structural and magnetic properties of Y3(GaAlFe)5O12 liquid-phase epitaxy films with low ferromagnetic resonance losses.

Ultra-thin rare earth iron garnet (RIG) films with a narrow ferromagnetic resonance (FMR) line width and a low damping factor have attracted a great deal of attention for microwave and spintronic applications. In this work, 200 nm Y3(GaAlFe)5O12 garnet (GaAl-YIG) films were prepared on gadolinium gallium garnet (GGG) substrates by liquid-phase epitaxy (LPE) with low saturation magnetization. The microstructural properties, chemical composition, and magnetostatic and dynamic magnetization characteristics of the films are discussed in detail. According to the structural analysis, these films exhibit a low surface roughness of less than 0.5 nm. The GaAl-YIG films show an obvious temperature dependence of lattice parameter and strain state, and the film's parameter is perfectly matched with that of the GGG substrate at 810°C. There is a clear variation in the Pb level, which brings about a gradual enhancement of the coercivity and a diminution of the squareness ratio of magnetic hysteresis loops as the growth temperature is reduced. Slight changes in surface roughness, strain condition and content of Pb induce the FMR line width and damping factor to vary on a small scale. The line width is less than 10.17 Oe at 12 GHz and the damping factor is of the order of 10-4. All these properties demonstrate that these ultra-thin GaAl-YIG films are of benefit for the development of devices operated at lower frequencies and in lower fields.

All Acoustical Excitation of Spin Waves in High Overtone Bulk Acoustic Resonator

The hybrid high overtone bulk acoustic wave resonators (HBARs) consisting of a piezoelectric film transducers and gallium gadolinium garnet substrates with yttrium iron garnet films (YIG-GGG-YIG) are used for experimental excitation and detection of acoustically driven spin waves (ADSWs). Two types of HBAR transducers made of Al-ZnO-Al films (differed through the electrodes’ geometry) were deposited onto YIG-GGG-YIG trilayers with different YIG film thicknesses and doping levels and served for excitation of multimode HBAR at gigahertz frequencies. ADSWs were detected by measuring the shifts of resonant HBAR modes in a tangential external magnetic field when the conditions for magnetoelastic resonance (MER) were satisfied. It was shown that the design of the transducer with a continuous bottom electrode provides all acoustical excitation of spin waves (pure ADSWs), suppressing the additional inductive magnetic dynamics excitation due to the electrodes’ geometry. The theoretical study of the HBAR spectrum in a magnetic field showed that the resonance harmonics in the MER region can either almost continuously transfer from one to another, or decay and form an evident magnetoelastic gap. In this case, the shift of resonant frequencies can achieve several intermodal distances. The results obtained are important for applications of HBAR-based devices in spintronics and magnonics.

Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications

We report the structural, magnetic, and interfacial spin transport properties of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron sputtering. High crystallinity was achieved by growing the films on gadolinium gallium garnet substrates either at high temperatures, or at room temperature followed by thermal annealing, above 750 °C in both cases. The films display large perpendicular magnetic anisotropy (PMA) induced by compressive strain, and tunable structural and magnetic properties through growth conditions or the substrate lattice parameter choice. The ferrimagnetic compensation temperature (TM) of selected TbIG films was measured through the temperature-dependent anomalous Hall effect in Pt/TbIG heterostructures. In the studied films, TM was found to be between 190 and 225 K, i.e., approximately 25-60 K lower than the bulk value, which is attributed to the combined action of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with large PMA and highly tunable properties reported here can provide a suitable material platform for a wide range of spintronic experiments and device applications.

Development of a Magnonic-Based Magnetic Sensor: Comparison of Two Different Implementations With YIG Material

In a ferromagnetic material exposed to a strong magnetic field, the spin wave describes the propagation of the phase shift of precessing spins at the same frequency over the time. In recent years, this subject has been of a great interest in the field of instrumentation and data transmission. Although several studies have shown a strong potential of magnonics for the design of a magnetic field sensor, few studies have been interested in the realization of such sensors and are limited to the measurement of scattering parameters. Here, we describe the development of a magnetic field sensor, using the variations in the propagation of the spin wave induced by the external magnetic field variation. We detailed the full implementation of the system, based on magnonics devices along with its associated electronic. The proposed implementation is mainly based on a quadrature I/Q demodulation to produce an output signal whose variations reflect the variations of the external applied magnetic field. The sensing element is designed from a yttrium iron garnet (YIG) film deposited on the gadolinium gallium garnet (GGG) substrate. It is placed on an optimized microstrip antenna transducer made of two copper lines, respectively, to excite and measure the spin waves. With the help of characterization measurements (S-parameters) carried out with a VNA, field sensitivities, expressed in V/T, could be estimated from S-parameters. Two kinds of magnonic devices have been implemented: one using spin-wave reflections at each YIG edge and other one using spacial filtering by YIG material microstructuring. Their performances regarding the magnetic sensitivity are compared. Finally, this first implementation of such a sensor, based on YIG magnonic material, exhibits a magnetic noise level of about 100 pT/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 1 kHz and a usable bandpass of 100 kHz. This is quite promising for a new sensor technology, leaving room for further developments.

Исследование зависимости сдвига линии ферромагнитного резонанса от параметров пьезоэлектриков

In this research, we study the dependence of the shift of the ferromagnetic resonance line in layered structures based on yttrium iron garnet (YIG) on a gadolinium gallium garnet (GGG) substrate, on the magnitude of the external electric field and on the parameters of various piezoelectrics (plumbum zirconate titanate (PZT), Langasite)). The intense development of modern microwave technology leads to the study and creation of new layered structures of materials with different physical properties that can be combined: magnetic and ferroelectric, magnetic and semiconductor, etc. As a result of the study, we obtained the dependences of the shifts of the ferromagnetic resonance line on the parameters of piezoelectrics (mainly, on the magnitude of the dielectric constant) in the layered structures YIG-GGGPZT, YIG-GGG-Langasite. The obtained results show that the ferromagnetic resonance line shift effect can be used to develop new controllable microwave devices, the operating principle of which is based on the electronic tuning of resonance characteristics by means of an electric field and the choice of the type of piezoelectric.

Magnetism and microstructure of co-deposited yttrium iron garnet-barium titanate films

Yttrium iron garnet (YIG) and barium titanate (BTO) were co-deposited on (001)-orientated gadolinium gallium garnet substrates by pulsed laser deposition with composition determined by the ratio of laser shots ablating each target. With increasing shot ratios of YIG/BTO = 2.5/1, 4/1, 20/1, and 30/1, the majority phase in the film changes from textured polycrystalline perovskite to epitaxial garnet. Cross-sectional STEM characterization of the YIG-rich films reveals three distinct sublayers: the bottom layer is a coherent epitaxial garnet layer with higher unit cell volume than that of YIG; the second layer is garnet exhibiting crystalline defects and misorientation; and the upper layer is amorphous. Highly defective regions within the second layer are richer in Ba, suggesting that the microstructure is promoted by the insolubility of Ba in YIG. Temperature-dependent magnetization measurements fitted to a super-exchange dilution model indicate the presence of nonmagnetic Ti and vacancies in both octahedral and tetrahedral sites.

The Effect of Ne+ Ion Implantation on the Crystal, Magnetic, and Domain Structures of Yttrium Iron Garnet Films

The mechanism of the influence of crystal inhomogeneities on the magnetic and domain microstructures of functional materials based on yttrium iron garnet heterostructures is an important subject of investigation due to the aim to predict parameters for manufacturingpurposes. A study of the structural and magnetic characteristics of a set of yttrium iron garnet films grown on gadolinium–gallium garnet substrate is presented. High-resolution X-ray diffractometry, Mössbauer spectroscopy, MFM, as well as ion implantation simulation and X-ray diffraction simulation were used together to determine the features of the effect of Ne+ ion implantation with different dose rates on the samples. The simulation of ion implantation with E = 82 keV showed energy loss profiles of Ne ions with subsequent defect formation up to amorphization of near-surface layers at high doses. Implantation creates two magnetically non-equivalent types of tetrahedrally located Fe3+ ions, which leads to a rotation of the total magnetic moment relative to the film surface and a change in the width of the magnetic domain stripes.

Observation of nonlinear planar Hall effect in magnetic-insulator–topological-insulator heterostructures

Interfacing topological insulators (TIs) with magnetic insulators (MIs) has been widely used to study the interaction between topological surface states and magnetism. Previous transport studies typically interpret the suppression of weak antilocalization or appearance of the anomalous Hall effect as signatures of magnetic proximity effect (MPE) imposed to TIs. Here, we report the observation of nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on MI thulium and yttrium iron garnet (TmIG and YIG) substrates, which is an order of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium gallium garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an extra hysteresis loop around zero field. The magnitude of the NPHE is found to scale inversely with carrier density. We speculate the observed NPHE is related to the MPE-induced exchange gap opening and out-of-plane spin textures in the TI surface states, which may be used as an alternative transport signature of the MPE in MI/TI heterostructures.

Tunable spin-wave delay line based on ferrite and vanadium dioxide

One of the key elements for modern microwave circuits is a delay line, which is widely utilized for the signal generation as well as processing. Spin-wave delay lines based on ferrite films provide a high delay time and small dimensions. Typically, the performance characteristics of such lines are tuned by the variation of an externally applied magnetic field characterized by some drawbacks. The phenomenon of a metal–insulator transition (MIT) in the phase change materials permits to improve the performance characteristics of the spin-wave delay lines. In particular, this concept allows to reduce the power consumption and improve the control speed of a delay time. Aim. Development of a tunable spin-wave delay line based on ferrite and vanadium dioxide films, as well as the study of its performance characteristics. Methods. Experimental investigations were carried out for the delay line composed of the yttrium iron garnet (YIG) and vanadium dioxide (VO2) films. The ferrite waveguide was fabricated from a single-crystal YIG film grown on a gallium gadolinium garnet substrate. A vanadium dioxide film was formed on a silicon dioxide substrate by DC reactive magnetron sputtering. The microwave measurements were carried out using the vector network analyzer R&amp;S®R ZVA40. Results. It was shown that heating of the VO2 film induces a sufficient drop of its resistance that causes the transformation of the spin-wave dispersion characteristic. This leads to the decrease in the group velocity of the propagating waves providing a growth of a delay time. Namely, experimental structure of 5-mm length offers a tunable time delay range from 130 up to 150 ns at the operating frequency of 4.33 GHz. Conclusion. A proof-of-principle for the MIT control of the delay time composed on the YIG-VO2 structure has been presented. It was shown that a switch of VO2 film from the isolating into conducting state produces a 15% change in the delay time. The considered microwave delay lines look favorable for applications as a complimentary part to the traditional approach for general computing and microwave signal processing.