Gadolinium Gallium Garnet Research Articles

Magnetism and site occupancy in epitaxial Y-rich yttrium iron garnet films

Y-rich yttrium iron garnet (Y-YIG) thin films were grown on gadolinium gallium garnet substrates using pulsed laser deposition from a ${\mathrm{YFeO}}_{3}$ target. The films are epitaxial on the substrate, and the unit cell of (001)- and (111)-oriented Y-YIG undergoes a tetragonal or rhombohedral distortion, respectively. The Y-YIG has lower room temperature magnetization but higher low-temperature magnetization than bulk YIG, and its Curie temperature was in the range of 330--400 K, depending on the growth conditions. First-principles calculations predict that ${\mathrm{Y}}_{\mathrm{Fe}}$ antisite defects are more stable in octahedral than tetrahedral Fe sites. Temperature-dependent magnetization measurements together with a superexchange dilution model and composition determined from x-ray photoelectron spectroscopy indicate that nonmagnetic species (${\mathrm{Y}}^{3+}$ and vacancies) are predominantly accommodated in the octahedral sites, but there is a significant occupancy of tetrahedral sites.

Large magnetocaloric effect in EuGd2O4 and EuDy2O4

Magnetization, heat capacity and direct measurements of the magnetocaloric effect show that EuGd2O4 and EuDy2O4 have a remarkably large magnetocaloric effect at cryogenic temperatures, owing to their high magnetic density and low ordering temperatures. The Gd derivative orders antiferromagnetically at TN = 4.6 K, while its magnetocaloric effect largely exceeds that of the reference refrigerant Gadolinium Gallium Garnet (GGG) above 5 K. The Dy derivative undergoes two phase transitions at TC1 = 3.65 K and TC2 = 4.7 K, respectively, which are the result of a peculiar magnetic arrangement: the first Dy sublattice is parallel to the crystallographic c-axis, while the Eu sublattice makes a variable angle from 0o to 45o with the direction of the second Dy sublattice that lies in the ab-plane. EuDy2O4 has a lower magnetocaloric effect than EuGd2O4, yet larger than GGG. Both ordering mechanisms are semi-quantitatively explained within the frame of a mean-field simulation, which takes into account the magnetic anisotropy strength of the participating magnetic ions.

Magnetism and spin transport in platinum/scandium-substituted terbium iron garnet heterostructures

Growth, structural, magnetic, and spin transport properties of epitaxial scandium-substituted terbium iron garnet (TbScIG) thin films on gadolinium gallium garnet [GGG, (111) orientation] substrates are reported as a function of Sc content. The films are epitaxial on GGG without strain relaxation up to a thickness of 90 nm and exhibit perpendicular magnetic anisotropy. Sc, a nonmagnetic cation, occupies up to 40% of the octahedral Fe sites. Increasing Sc lowers the compensation temperature and Curie temperature and increases the room-temperature saturation magnetization from 37 kA/m for ${\mathrm{Tb}}_{2.8}{\mathrm{Fe}}_{5.2}{\mathrm{O}}_{12}$ to 59 kA/m for ${\mathrm{Tb}}_{2.8}{\mathrm{Sc}}_{0.8}{\mathrm{Fe}}_{4.4}{\mathrm{O}}_{12}$. Anomalous Hall effect-like spin Hall magnetoresistance measurements were performed to determine the effect of scandium content on spin mixing conductance of the TbScIG|Pt interface. The spin mixing conductance increased significantly with an increase in Sc content, consistent with a dependence of spin transport on the net Fe magnetization instead of the total magnetization of the garnet.

Optical emission of shocked magnesium oxide single crystals: Heat-conduction and orientation effects

To investigate light emission properties of shocked high-conductivity single crystals during plastic deformation, [100] and [110] magnesium oxide (MgO) single crystals are shock-compressed up to 64 GPa via a planar impact. [111] gadolinium–gallium garnet (GGG) and [100] Y-stabilized zirconate (YSZ) single crystals, respectively, with intermediate and low conductivities are also examined for comparison. Emission spectral radiance and velocity histories are simultaneously measured with a fast, high-sensitivity pyrometer and a Doppler pin system. While velocity histories of [100] MgO, [111] GGG, and [100] YSZ show typical two-wave structures at elastic–plastic transition, abnormal three-wave structures are observed for [110] MgO, consistent with literature reports. Correspondingly, spectral radiance histories of [100] MgO, [111] GGG, and [100] YSZ under each tested stress demonstrate a typical “single-wave” structure, while a “two-wave” structure is observed for [110] MgO shocked to 33–37 GPa. The peak intensities of spectral radiance for both [100] and [110] MgO are much lower than those of GGG and YSZ shocked to similar plastic strains as a result of different heat conductivities. A model, taking into account heat conduction from a shear band into its surrounding bulk areas and two-zone emission, is thus developed and describes well the measurements. Our observations make a concrete connection between shear banding and localized heating/cooling as proposed previously.

Micro-nanoscale Loop-shaped Mircowave Antenna for Exciting Spin Waves on Magnetic Materials

In this paper, loop-shaped microwave antenna in the scale of micro- and nanometer loop-shapedis designed to excite and detect spin waves. We consider that spin waves propagate in the yttrium iron garnet (YIG) films grown on gadolinium gallium garnet (GGG) substrate with lowest damping. Loop-shaped microwave antenna is made of loop-shaped gold, which is used to excite the Co disks grown on YIG film and spin waves propagating in YIG film. Firstly, the high-frequency structure simulator (HFSS) is used to simulate the current, magnetic field distributon and input resistance of the loop-shaped antenna. In addition, the k distribution of the antenna is obtained by using the fast Fourier transform (FFT). The influence of different matching degrees of the antenna on k distribution is analyzed. The kind of antenna can be used to produce different modes of spin waves.

Magnetic Properties and Growth‐Induced Anisotropy in Yttrium Thulium Iron Garnet Thin Films

AbstractRare‐earth iron garnets (REIG) have recently become the materials platform of choice for spintronic studies on ferrimagnetic insulators. However, thus far the materials studied have mainly been REIG with a single rare earth species such as thulium, yttrium, or terbium iron garnets. In this study, magnetometry, ferromagnetic resonance, and magneto‐optical Kerr effect imaging is used to explore the continuous variation of magnetic properties as a function of composition for YxTm3−x iron garnet (YxTm3−xIG) thin films grown by pulsed laser deposition on gadolinium gallium garnet substrates. It is reported that the tunability of the magnetic anisotropy energy, with full control achieved over the type of anisotropy (from perpendicular, to isotropic, to an in‐plane easy axis) on the same substrate. In addition, a nonmonotonic composition‐dependent anisotropy term is reported, which is ascribed to growth‐induced anisotropy similar to what is reported in garnet thin films grown by liquid‐phase epitaxy. Ferromagnetic resonance shows linear variation of the damping and the g‐factor across the composition range, consistent with prior theoretical work. Domain imaging reveals differences in reversal modes, remanant states, and domain sizes in YxTm3−x iron‐garnet thin films as a function of anisotropy.

Generation of few-cycle laser pulses at 2 μm with passively stabilized carrier-envelope phase characterized by f-3f interferometry

We report on generation and characterization of few-cycle laser pulses with the central wavelength of 2 μm at repetition rate of 50 kHz. The source is based on noncollinear parametric amplification and difference frequency generation leading to passively stabilized carrier-envelope phase (CEP). CEP is characterized using f-3f technique based on spectral interference between the fundamental spectrum broadened via self-phase modulation and the third harmonics, which are both generated by tight focusing of the pulses to gallium gadolinium garnet (GGG) crystal. We demonstrate the capability of this technique for CEP measurement and long-term stabilization. Further we show that the pulses can be compressed to a duration of 1.7 optical cycles after spectral broadening in the GGG crystal.

Spin current and spin waves at a platinum/yttrium iron garnet interface: impact of microwave power and temperature

The spectra of ferromagnetic resonance and spin current of the heterostructure consisting of an epitaxial film of yttrium iron garnet Y3Fe5O12 (YIG) grown on a gallium gadolinium garnet (Gd3Ga5O12) substrate and with 10 nm thick platinum (Pt) film on top were studied at frequencies f = 2–18 GHz under applied power in the range of 20 μW–50 mW as well as temperatures T = 77–300 K. The standing spin-wave resonances (SWRs) with both magnetostatic backward volume spin waves and magnetostatic surface spin waves (MSSWs) were detected. The SWR evolution was investigated with change of microwave power. Due to generation of spin current perpendicular to the Pt/YIG interface and the inverse spin Hall effect the charge current on the Pt film was registered and analyzed. The SWR resulted in deviations of spin current spectral lines from a Lorentz line form, indicating that at high microwave power the main contribution is made by MSSW. As the temperature decreases, the amplitude of the spin current decreases, although the width of the spectral line remains the same while the magnetization increases at lower temperatures. A decrease in spin Hall angle with cooling may explain this behavior of the spin current at low temperatures.

Control of magnetization dynamics by substrate orientation in YIG thin films

Yttrium Iron Garnet (YIG) and bismuth (Bi) substituted YIG (Bi0.1Y2.9Fe5O12, BYG) films are grown in-situ on single crystalline Gadolinium Gallium Garnet (GGG) substrates [with (100) and (111) orientations] using pulsed laser deposition (PLD) technique. As the orientation of the Bi-YIG film changes from (100) to (111), the lattice constant is enhanced from 12.384 Å to 12.401 Å due to orientation dependent distribution of Bi3+ ions at dodecahedral sites in the lattice cell. Atomic force microscopy (AFM) images show smooth film surfaces with roughness 0.308 nm in Bi-YIG (111). The change in substrate orientation leads to the modification of Gilbert damping which, in turn, gives rise to the enhancement of ferromagnetic resonance (FMR) line width. The best values of Gilbert damping are found to be (0.54 ± 0.06) × 10−4, for YIG (100) and (6.27 ± 0.33) × 10−4, for Bi-YIG (111) oriented films. Angle variation (ϕ) measurements of the Hr are also performed, that shows a four-fold symmetry for the resonance field in the (100) grown film. In addition, the value of effective magnetization (4πMeff) and extrinsic linewidth (ΔH0) are observed to be dependent on substrate orientation. Hence PLD growth can assist single-crystalline YIG and BYG films with a perfect interface that can be used for spintronics and related device applications.

Assessing the quality of polished brittle optical crystal using quasi-Brewster angle technique

Polishing is a main process in achieving high-quality surfaces of optical components. However, effective assessing technique for rough stage in the polishing process is sparse so that hinders the study on the mechanism and optimization of polishing. In this study, we propose an inspection method for polishing quality based on quasi Brewster angle technology (qBAT). An equivalent medium layer theory and its model are developed to accurately describe the optical reflection characteristics of a rough surface. Hence both rough- and fine-polishing qualities can be evaluated by the qBAT approach. To demonstrate the newly proposed method, laser crystal, gadolinium gallium garnets, is studied by computational simulation and experiments. A high consistence is achieved between theoretical simulation and experimental results, which proves the robustness of the method to the rough surfaces. To our knowledge, it is the first time that the qBAT is developed to evaluate the polishing quality covering rough- and fine-polishing stages. This capability shows great potential in fundamental research and process optimization of polishing brittle-hard materials.

Large Magnetocaloric Effect in Li3K9Gd3(BO3)7 Crystal Featuring Sandwich-Like Three-Dimensional Framework.

A new Gd-based borate crystal, Li3K9Gd3(BO3)7, has been successfully obtained via the high-temperature solution method using Li2O-K2O-B2O3 self-flux. It crystallizes in monoclinic space group P2/n (no. 10) with lattice parameters a = 11.3454(6) Å, b = 9.9881(4) Å, c = 11.4467(7) Å, α = γ = 90 o, β = 114.782(7) o, and Z = 2. Li3K9Gd3(BO3)7 exhibits an intriguing sandwich-like three-dimensional (3D) framework constructed from [Gd-B-O]∞ layers, KOn (n = 6 and 8) polyhedra, and LiO4 tetrahedra, in which [Gd-B-O]∞ layers are built from two types of GdO8 polyhedra and triangular BO3 units. Magnetic measurements showed that Li3K9Gd3(BO3)7 exhibits a large magnetocaloric effect with -ΔSm = 39.3 J kg-1 K-1 at 2.0 K for ΔH = 7 T, which is slightly higher than that of the commercial gadolinium gallium garnet under the same conditions. The powder X-ray diffraction, infrared spectrum, and UV-vis-NIR diffuse reflectance spectrum were also performed to characterize Li3K9Gd3(BO3)7. The electronic band structures, partial density of states, and refractive indices of Li3K9Gd3(BO3)7 were investigated via the first-principle calculations.

Tunable Magnetoacoustic Oscillator with Low Phase Noise

A frequency-tunable low-phase-noise magnetoacoustic resonator is developed on the base of a parallel-plate straight-edge bilayer consisting of an yttrium-iron-garnet (YIG) layer grown on a substrate of a gallium gadolinium garnet (GGG). When a YIG-GGG sample forms an ideal parallel plate, it supports a series of high-quality-factor acoustic modes standing along the plate thickness. Due to the magnetostriction of the YIG layer the ferromagnetic resonance (FMR) mode of the YIG layer can strongly interact with the acoustic thickness modes of the YIG-GGG structure, when the modes' frequencies match. A particular acoustic thickness mode used for the resonance excitations of the hybrid magnetoacoustic oscillations in a YIG-GGG bilayer is chosen by the YIG-layer FMR frequency, which can be tuned by the variation of the external bias magnetic field. A composite scheme of a magnetoacoustic oscillator, which includes a FMR-based resonance preselector, is developed to guarantee satisfaction of the Barkhausen criteria for a single-acoustic-mode oscillation regime. The developed low-phase-noise composite magnetoacoustic oscillator can be tuned from 0.84 to 1 GHz with an increment of about 4.773 MHz (frequency distance between the adjacent acoustic thickness modes in a YIG-GGG parallel plate), and demonstrates the phase noise of $\ensuremath{-}116$ dBc/Hz at the offset frequency of 10 kHz.

Development of White Persistent Phosphors by Manipulating Lanthanide Ions in Gadolinium Gallium Garnets

Lanthanide ions act as excellent luminescence centers and good charge carrier traps. By selecting proper lanthanide ions, persistent phosphors with the desired luminescent color can be developed. In addition, an appropriate host material can give not only better persistent luminescence performance but also an additional function. Herein, bright white persistent phosphors of Pr3+–Tb3+–Eu3+ tridoped paramagnetic Gd3Ga5O12 (GGG) are successfully developed. The GGG phosphors singly doped with Pr3+, Tb3+, and Eu3+ show reddish‐white (3PJ–3HJ), blue (5DJ–7FJ), and red (5D0–7FJ) photoluminescence, respectively, by UV excitation. On the other hand, the GGG samples codoped with Pr3+–Eu3+ and with Tb3+–Eu3+ show only Pr3+ reddish‐white persistent luminescence and Tb3+ blue persistent luminescence, respectively. Based on the thermoluminescence glow curves, it is found that the Eu3+ ion acts only as an electron trap in the persistent luminescence mechanism and the trapped electrons are released at around 325 K. The cool‐white persistent luminescence is achieved by combining Pr3+ and Tb3+ persistent luminescence centers in the GGG:Pr3+–Tb3+–Eu3+ phosphors. It is demonstrated that the white persistent phosphor powder in water can be dragged around by a permanent magnet due to the paramagnetic property of GGG.

Preferred‐oriented polycrystalline Y3Fe5O12 films grown on quartz with low microwave loss

AbstractYttrium iron garnet (YIG) is an ideal magnetic insulator for room temperature microwave and spintronic applications. The growth of high‐quality YIG films on substrates other than isostructural Gadolinium gallium garnet (GGG) is a primary requirement to integrate with current semiconductor electronics. Here, we are presenting the growth of highly oriented YIG films on amorphous quartz substrates using pulsed laser deposition. Structural characterization suggests the growth of pure polycrystalline garnet phase with preferred (100) orientation. The 430‐nm thick YIG film shows a saturation magnetization (4πMS) of 1620 (92% of the bulk value of YIG) with a very small coercive field of 6 Oe and a minimum value for ferromagnetic resonance linewidth of 78 Oe for the magnetic field applied perpendicular to the film plane. Estimated damping constant shows reasonably low value, beneficial for realizing the applications integrated with semiconductor technology. Importantly, the formation of YIG with preferred orientation could unveil enormous opportunities in the preparation of textured or single crystal materials on amorphous substrates.

Coexistence of the electric polarization and conductive current in the bismuth–neodymium ferrite garnet films

The Nd1Bi2Fe5O12/Nd2Bi1Fe4Ga1O12 polycrystalline films on the glass substrate and the Nd0.5Bi2.5Fe5O12 epitaxial films on the single-crystal gadolinium gallium garnet substrate have been investigated by impedance and dielectric spectroscopy. The inductive contribution to the impedance and two relaxation channels related to ferroelectric domains and migration polarization have been established. The magnetocapacitance and magnetoimpedance have been determined. The conductive and polarization currents and the phase difference between them for the films of two types have been determined. The critical temperatures of the polarization disappearance and hysteresis I–V have been found. A model of the polarization caused by the piezoelectric effect and flexoelectric interaction has been proposed. I–V hysteresis is explained by the presence of ferroelectric domains near the interface and is associated with the hysteresis of the electric polarization.

Отрицательное магнитосопротивление в структуре n-InSb/ЖИГ

It is shown that for the n-InSb/YIG/GGG (YIG - yttrium iron garnet, GGG - gallium-gadolinium garnet) structure in the tangent to the substrate plane geometry of magnetization (H <10 kOe) at a temperature T≈300 K the magnetoresistance of about 1% is negative, while for n-InSb/GGG structure, in the same magnetization geometry, the magnetoresistance is positive (an increase in electrical resistance in a magnetic field). The negative magnetoresistance effect in the InSb/YIG/GGG structure is due to the influence of the YIG magnetization on the conduction electrons of InSb (proximity effect) and the magnitude of the effect is determined by the value of YIG magnetization and parameters of InSb films.

Ultra-low temperature adiabatic demagnetization refrigerator for sub-Kelvin region

<sec>With the development of space observation, quantum technology and other frontier scientific research fields, the demand for ultra-low temperature refrigeration in sub-Kelvin region is increasing. Compared with dilution refrigeration and sorption refrigeration, adiabatic demagnetization refrigeration (ADR) has the outstanding advantages of high efficiency, compact, gravity independence and accessibility of working materials, which make ADR a promising technology for sub-Kelvin cooling.</sec><sec>A single-stage ultro-low temperature adiabatic demagnetization refrigerator is designed and developed. The thermodynamic principle and quantitative analysis are presented, from the macroscopic and microcosmic view, and operating results show good agreement with the theoretical value.</sec><sec>This refrigerator is precooled to 3 K by a GM-type refrigerator, with 252 g gadolinium gallium garnet (monocrystalline) used as a working medium. The maximum magnetic field of 4 T is provided by a superconducting coil. Flexible heat connection is used between the pre-cooler and ADR, so heat generated by vibration decreases. From (3 K, 4 T), the lowest temperature can reach 0.47 K by adiabatic demagnetization, which is consistent with the result drawn from the entropy data. In a constant-temperature-control mode, the demagnetization rate is controlled by a feedback loop, so the temperature can be held in the presence of a load. A cooling capacity of 2.7 J is provided at 1 K, with temperature fluctuation being lower than 0.5 mK, and the second thermodynamic efficiency of adiabatic demagnetization refrigeration is 57%. at 0.8 K, the cooling capacity is 1.2 J.</sec><sec>Future work on improving the performance includes the improving of the on-off ratio of the heat switch, so, the irreversible loss caused by the heat transfer temperature difference in conduction state can be reduced. Improving the heat transfer performance of the salt pill, the heat can be ejected in a shorter period.</sec><sec>This refrigerating machine is the first Chinese adiabatic demagnetization refrigeration system that can be operated in circulation, which is expected to be the 1<sup>st</sup> stage of a three-stage adiabatic demagnetization refrigeration system in a 50 mK temperature zone. This study lays a foundation for further developing continuous multistage adiabatic demagnetization refrigeration at ultra-low temperature.</sec>

Dynamic Magnonic Crystals for Measuring the Dispersion of Bulk Magnetostatic Spin Waves Caused by Magnetic Anisotropy in YIG Films

A dynamic magnonic crystal created by a surface acoustic wave that propagates in a GGG–YIG structure (gallium–gadolinium garnet–yttrium–iron garnet) is used to measure the dispersion of bulk magnetostatic waves due to the magnetic anisotropy in the YIG film. Such waves, which are called anisotropic-dipole magnetostatic waves (ADMSWs), can propagate together with surface spin waves in YIG films that are placed in a tangential magnetic field. It is shown experimentally that ADMSWs with a positive dispersion law occur in films that are grown by the liquid-phase epitaxy technique and not subjected to additional processing,. In the films that were subjected to additional processing the ADMSW dispersion law is negative when applying a piezoelectric zinc oxide film or bombarded with boron ions.

Epitaxial growth of Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> films with perpendicular magnetic anisotropy and spin transport properties in Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>/Pt heterostructures

Rare-earth iron garnet films with perpendicular magnetic anisotropy could open new perspectives for spintronics. Holmium iron garnet (Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>, HoIG) films with thickness ranging from 2 to 100 nm are epitaxially grown on (111) orientated gadolinium gallium garnet single crystal substrate doped with yttrium and scandium (Gd<sub>0.63</sub>Y<sub>2.37</sub>Sc<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub>, GYSGG) by ultra-high vacuum magnetron sputtering. A 3-nm Pt film is further deposited on each of the HoIG films. The magnetic anisotropy and magneto-transport properties of heterostructures at room temperature are investigated. It is shown that the HoIG film as thin as 2 nm (less than two unit cells in thickness) exhibits the ferromagnetic properties at room temperature, and perpendicular magnetic anisotropy is achieved in the 2-60 nm thick films, and a maximum effective perpendicular anisotropy field reaches 350 mT due to the strain induced magnetoelastic anisotropy. The HoIG/Pt heterostructure shows significant anomalous Hall effect (AHE) and appreciable spin-Hall magnetoresistance (SMR) and/or anisotropic magnetoresistance (AMR). Remarkably, the AHE starts to decline gradually when the HoIG thickness is less than 4 nm, but the magnetoresistance decreases rapidly with the HoIG layer becoming less than 7 nm in thickness. The fact that the AHE in the heterostructure is less sensitive to the HoIG thickness suggests that the interface effect is more dominant in the AHE mechanism, whereas the bulk magnetic properties of the HoIG plays a more important role for the observed magnetoresistance. In addition, the spin Seebeck effect decreases exponentially with the decrease of HoIG thickness till the ultrathin limit, which was previously validated in the micrometer-thick YIG/Pt stacks in the frame of thermally excited magnon accumulation and propagation. The present results show that the nanometer HoIG/Pt heterostructure with tunable perpendicular magnetic anisotropy and efficient interfacial spin exchange interaction could be a promising candidate for insulating magnet based spintronic devices.

Soft photon study at NICA’s facilities

For over three decades there has been no comprehensive understanding of the mechanism of soft photon (energy smaller than 50 MeV) formation. Experimental data indicate an excess of their yield in hadron and nuclear interactions in comparison with calculations performed theoretically. In JINR, in connection with the building of a new accelerator complex NICA, it has become possible to carry out such studies in pp, pA and AA interactions at energies up to 25 A GeV. We prepared the extensive physical program for soft photons that covers the wide region of investigations in high energy physics. To carry out this program our group develops the conception of an electromagnetic calorimeter on type “shashlik” based on gadolinium-gallium garnet (GaGG) crystals, which have a significantly lower threshold for the registration of photons. The first tests of electromagnetic calorimeters manufactured at the Joint Institute for Nuclear Research on the basis of the GaGG crystals and a composite of tungsten and copper are reported.