Gallium Substituted Yttrium Iron Garnet Research Articles

Nonlinear erasing of propagating spin-wave pulses in thin-film Ga:YIG

Nonlinear phenomena are crucial for magnon-based information processing, but the nonlinear interaction between two spin-wave signals requires their spatiotemporal overlap, which can be challenging for directional processing devices. Our study focuses on a gallium-substituted yttrium iron garnet film, which exhibits an exchange-dominated dispersion relation and, thus, provides a particularly broad range of group velocities compared to pure YIG. Using time- and space-resolved Brillouin light scattering spectroscopy, we demonstrate the excitation of time-separated spin-wave pulses at different frequencies from the same source, where the delayed pulse catches up with the previously excited pulse and outruns it due to its higher group velocity. By varying the excitation power of the faster pulse, the outcome can be finely tuned from a linear superposition to a nonlinear interaction of both pulses, resulting in a full attenuation of the slower pulse. Therefore, our findings demonstrate the all-magnonic erasing process of a propagating magnonic signal, which enables the realization of complex temporal logic operations with potential application, e.g., in inhibitory neuromorphic functionalities.

Nonreciprocal propagation in optical fibers

Nonreciprocal propagation in the structures compatible with optical fiber waveguides presents practical interest. The present work treats the problem of nonreciprocal propagation in nonabsorbing cylindrically layered structures at axial magnetization characterized by magneto-optic electrical permittivity, , and magnetic permeability, , tensors, using transverse circularly polarized representation. The solutions to the vector Helmholtz Eqs. restricted to the terms linear in the off-diagonal elements of and are expressed analytically. The results are applied to a magneto-optic circular cylindrical waveguide and illustrated on fiber waveguides with an yttrium iron garnet (YIG) core and a cladding formed by gallium substituted yttrium iron garnet (GaYIG) at the optical communication wavelength of 1.55 μm. The propagation distance in the waveguide for a azimuth rotation of a transverse linearly polarized incident wave on the waveguide axis required in isolators is about 100 μm.

Rigorous broadband study of the intrinsic ferromagnetic linewidth of monocrystalline garnet spheres

This work demonstrates the first application of direct broadband (1 GHz–30 GHz) quality (Q) factor measurements of the uniform precession mode in magnetised garnet spheres for the accurate determination of the room-temperature intrinsic ferromagnetic linewidth (ΔH). The spheres were enclosed in a subwavelength cavity, so that the measured Q-factor depended mainly on their magnetic losses and the conduction losses of the cavity walls. The contribution of the latter is assessed by means of the recently proposed magnetic plasmon resonance model and has been found to be negligible. A total of 10 samples made from commercially available pure yttrium iron garnet (YIG) and gallium-substituted YIG have been measured, differing in diameter and/or saturation magnetisation Ms. The dependence of the intrinsic ΔH on the internal magnetic field is found to have near-perfect linear dependence, which cannot be said about the typically studied extrinsic ΔH even at high frequencies. It is found that the difference between the two linewidths, which becomes significant at low frequencies, can be attributed to a geometric effect. Due to its fundamental nature, this work is applicable not only to magnetic material characterization, but also to the study of the origins of losses in magnetic materials.

Magnetooptics in Cylindrical Structures

Understanding magnetooptics in cylindrical structures presents interest in the development of magnetic sensor and nonreciprocal devices compatible with optical fibers. The present work studies wave propagation in dielectric circular cylindrical structures characterized by magnetic permeability and electric permittivity tensors at axial magnetization. The Helmholtz equations deduced from the Maxwell equations in transverse circularly polarized representation provide electric and magnetic fields. With the restriction to terms linear in off-diagonal tensor elements, these can be expressed analytically. The results are applied to magnetooptic (MO) circular cylindrical waveguides with a step refractive index profile. The nonreciprocal propagation is illustrated on waveguides with an yttrium iron garnet (YIG) core and a lower refractive index cladding formed by gallium substituted yttrium iron garnet (GaYIG) at the optical communication wavelength. The propagation distance required for the isolator operation is about one hundred micrometers. The approach may be applied to other structures of cylindrical symmetry in the range from microwave to optical frequencies.

Application of the smith chart in the analysis of the relaxation properties of magnetostatic oscillations and spin waves in ferrite films

The relaxation properties of three main types of magnetostatic oscillations in a magnetostatic film resonator and nonlinear processes (parametric excitation of spin waves in the first and second bands in the presence of the tangential magnetization of the gallium-substituted yttrium-iron garnet film and foldover in the regime of normal magnetization) are studied in the frequency range 0.8–4.5 GHz. An original method is proposed for the determination of thresholds of the parametric excitation of spin waves using the deformations of Smith chart caused by variations in the measurement power level. The method is used in the highaccuracy analysis of the frequency dependences of threshold power in the presence of tangential magnetization in the regimes of resonances of both surface and backward volume magnetostatic waves. The frequencyfield dependences of the absorption spectra of three main types of magnetostatic oscillations in the linear regime are used to determine the saturation magnetization, anisotropy fields, and unloaded Q factors of resonator at each mode and to calculate the relaxation parameters of the corresponding magnetostatic oscillations. The experimentally measured threshold pump powers are used to calculate the relaxation line widths of the parametrically excited spin waves with the aid of the improved theory of parametric processes that takes into account both cubic and uniaxial anisotropy of the film.

Preparation of Magneto-Optic Single-Mode Buried Channel Waveguides of Lanthanum- and Gallium-Substituted Yttrium Iron Garnet

Magneto-optic single-mode buried channel waveguides are prepared using lanthanum- and gallium-substituted yttrium iron garnet [(La, Ga):YIG] liquid-phase-epitaxial film. The film growth conditions, film properties and the core ridge fabrication method are described. The refractive index of the film is controlled with the film growth temperature. The core ridge size is well controlled using ion beam etching. The obtained waveguides provide low loss coupling with a silica-based waveguide, which is a platform waveguide for a hybrid optical integrated circuit. Magneto-optic mode conversion is observed in a weak applied magnetic field, and the conversion efficiency R max and isolation ratio are evaluated. The relationship between R max and the stress-induced birefringence is discussed.

Submicroampere-per-root-hertz current sensor based on the Faraday effect in Ga:YIG

We demonstrate an optical current sensor that is based on the Faraday effect in gallium-substituted yttrium iron garnet and has a measured sensitivity of ∼3°/A, a noise-equivalent current of ~220nA/Hz, and a −3-dB bandwidth of ∼2.6 MHz. The bandwidth–sensitivity product is a factor of ∼10 greater than that of an all-silica-fiber current sensor with the same diameter.

Magneto-optic magnetic field sensor with 1.4 pT/√(Hz) minimum detectable field at 1 kHz

The Letter demonstrates that the sensitivity of magneto-optic magnetic field sensors employing iron garnets can be increased by approximately two orders of magnitude by applying flux concentration. A minimum detectable field of 1.4 pT/√(Hz) was measured when a cylindrical gallium-substituted yttrium iron garnet crystal was combined with two conically tapered nickel–zinc ferrite cylinders.

Influence of Growth Temperature on the Magnetic and Optical Properties of Liquid-Phase-Epitaxial(LPE)-Grown Lanthanum- and Gallium-Substituted Yttrium Iron Garnet ((La, Ga):YIG) Films and Their Application to Waveguides

We measure the growth temperature dependence of the magnetic and optical properties of lanthanum- and gallium-substituted yttrium iron garnet films deposited on gadolinium gallium garnet substrates by the liquid-phase-epitaxial-growth method for use as integrated optical waveguides. The magnetization of the film can be saturated in the film plane by a weak external-magnetic field (<45 Oe). The refractive index is controlled in a range of 2.192 to 2.204 by the growth temperature, which ranges from 893 to 835°C. Rib waveguides with low propagation loss (2.3 dB/cm at 1.55 µm wavelength evaluated by measuring the contrast in Fabry-Perot cavity resonance signals) are also fabricated.

Measurements of Faraday effect in iron garnet optical waveguide at near infrared wavelengths

The Faraday rotation constants in a magneto-optic channel waveguide whose magnetization aligns along the direction of propagation are measured by a novel method developed by the authors. The tested sample is a lanthanum and gallium substituted yttrium iron garnet optical channel waveguide prepared by the liquid phase epitaxial and the ion milling techniques. The proposed method is more practical than the previously reported one because of determination of the parameters with one time measurement. In the previous method we needed to know the phase constant difference between the orthogonally polarized waves to determine the Faraday coefficient. Using the presented technique we successfully measure the magneto-optic coefficients in the iron garnet waveguide at the near infrared wavelengths: 1.15, 1.3, and 1.55 μm. We confirm the validity of the proposed method by comparing with other methods: the previously reported method and the Faraday modulation method conventionally used for measuring the Faraday rotation. We also demonstrate the waveguide isolator operation.

Improvements in the differential phase shift of magneto-optic waveguides by loading with high refractive index overlayers

Experimental results are presented for a nonreciprocal phase shift of vertically polarized waves in four-layer magneto-optic rib waveguides. The structure consists of a high refractive index nonmagnetic layer of titanium oxide on top of a magneto-optic film (a lanthanum and gallium substituted yttrium iron garnet film on a gadolinium gallium garnet substrate) to improve differential phase characteristics. The difference of phase constants for waves traveling in opposite directions is evaluated by observing the variation in the polarization coupled out of a straight waveguide when simultaneously exciting both horizontally and vertically polarized waves with equal amplitudes and phases. The phase shift difference varies with the thickness of the nonmagnetic film, and is larger than that of a previous three-layer waveguide in the overlayer thickness range 0.15–0.45 μm. The maximum phase shift obtained is 2.5 times as large as that of uncoated waveguides.

INFLUENCE OF EPITAXIAL GROWTH RATE ON THE OPTICAL LOSS OF GdxY3_xGayFe5_yO12 MONO AND MULTILAYER FOR AN INTEGRATED SINGLE MODE OPTICAL ISOLATOR

A single mode integrated magnetooptical isolator requires a propagating media having the fol-lowing properties: low propagation loss, a thickness within the range of the core diameter of single mode optical fibers and a magnetization in the plane of the guide. In the near infrared region (λ = 1.1 μm - 1.6 μm), these requirements can be obtained through the use of gadolinium gallium substituted yttrium iron garnet (YIG) films grown by liquid phase epitaxy. At 1.15 μm, calculations show that a single mode optical isolator is the result of a double substituted structure such as GdO.45Y2.55Ga0.8Fe4.2O12/GdO.45Y2.55GaO.9Fe4.1O12/Gd3Ga5O12.To master the growth process of these layers, we have investigated the var1at1on of the optical loss of single and double YIG films versus growth rate. The results fit a parabolic curve. SIMS analysis were performed on these substrates and we discovered that (Pb-2Pt) exhibit an important role as decreasing with optical loss.

Magnetostatic wave devices for UHF band applications

Magnetostatic surface wave (MSSW) devices made with pure and gallium-substituted yttrium-iron garnet (Ga:La-YIG) films are described. These devices include nondispersive and dispersive delay lines, band-pass filters, oscillators, and resonators. By controlling the magnitude of the bias magnetic field and the temperature of operation, it is possible to tune these devices over a wide frequency range extending from 0.3 to 4 GHz and from 3 to 18 GHz using Ga:La-YIG and pure YIG films, respectively.

Influence of Growth Temperature on the Optical Properties of (YBi)3(FeGa)5O12 Film Waveguides

We report measurements of the optical properties of bismuth and gallium substituted yttrium iron garnet films deposited on GGG substrates by the LPE method for use as integrated optical waveguides. Emphasis is placed on the effect of the growth temperature. As the degree of supercooling was increased from 0.02 to 0.1 for a melt whose saturation temperature was 985°C, the refractive index of the film varied from 2.17 to 2.23 and the Faraday rotation varied from 200 to 800 degree/cm at a wavelength of 1.15 µm. However, the mode propagation loss was constant at nearly 10 dB/cm regardless of the growth temperature.

Homogeneity of YGaIG single crystal grown by the FZ method

Single crystals of gallium-substituted yttrium iron garnet (YGaIG) having several compositions were grown by the floating zone melting technique and the distribution of the magnetic properties and Ga contents in the Y 3 Fe 5-x Ga x O 12 system along cross sections parallel and perpendicular to the growth direction were investigated. The preparation of specimens was made on compositions Y 3 Fe 5-x Ga x O 12 , x=0.9,1.0 and 1.2. The pollycrystalline specimen rods, 10mm in diameter and 100mm in length, were crystallized using an apparatus of infrared radiation convergence type. Distribution of saturation magnetization (4πM s ) were measured using a magnetic balance. The measurements on ferromagnetic resonance line width (ΔH) were carried out by coupling 0.66mm spheres with transmission line at 4GHz. The results for specimens having 4\piM_{s}\simeq600 Gauss showed that (4πM s ) distribution at the core portion along the direction of crystal growth were ±6.9%, whereas within a cut plane perpendicular to the growth direction (4πM s ) distribution were ±2.4%. ΔH at the central part was from 0.6-1.0 Oersted. Analysis for gallium was carried out by X-ray microanalyzer and the distribution along the direction of crystal growth was found to be within ±0.34 mo1% against meanvalue.

Computer Simulation of Temperature and Field Dependences of Sublattice Magnetizations and Spin-Flip Transition in Gallium-Substituted Yttrium Iron Garnet

On the basis of the molecular field model, sublattice magnetizations in gallium-substituted yttrium iron garnet Y 3 Ga x Fe 5- x O 12 are calculated over a wide range of x , temperature and applied magnetic field with a computer program. Comparing the calculated temperature dependence of spontaneous magnetization, the critical fields of the spin-flip transition at high magnetic fields and the ferrimagnetic Curie temperature, with experimental data, the super-exchange coefficients in YIG and Y 3 Ga x Fe 5- x O 12 were evaluated.

Relaxation processes in polycrystalline substituted garnets with low ferrimagnetic resonance linewidth

The broadening of the ferrimagnetic resonance (FMR) linewidth by two-magnon scattering processes has been studied on various extremely dense substituted garnets with different In or Zr substitutions for anisotropy field reduction. The observed frequency dependent linewidths ranging between 0.6 and 30 Oe have been completely resolved into anisotropy and porosity-induced scattering processes and intrinsic losses. Excellent agreement was found with Schlömann's anisotropy line broadening theory which was applied to determine the unknown anisotropy fields of the investigated polycrystalline garnets. The contradiction of the experimental findings for the porosity-induced scattering contributions with theoretical predictions is discussed together with the spin wave dispersions properties, and a suitable perturbation model for scattering to low and do high k-states of the spin wave manifold is proposed. Extremely low residual porosities of 0.04% have been found for several garnet compositions. The observed intrinsic losses are nearly identical to that of single crystal gallium substituted yttrium iron garnet (YIG) with the same 4π M s value. Several substituted garnets showed additional losses with an approximate 1/ H 1 dependence. The origin of the associated relaxation process could not be interpreted unequivocally.

Anisotropy and magnetostriction of gallium-substituted yttrium iron garnet

The anisotropy and magnetostriction constants of gallium-substituted yttrium iron garnet single crystals of composition Y3Fe5−tGatO12 with 0≤t≤1.5 have been investigated by means of ferrimagnetic resonance in the temperature range 4.2≤T≤500 K. From the concentration dependence at T =4.2 K the single-ion contribution of the tetrahedral and octahedral anisotropy was found to be Kd = −0.0019 cm−1 and Ka = −0.012 cm−1, respectively. In the range t&amp;lt;1 of linear concentration dependence of the magnetostriction constants at T=4.2 K, a variation Δλ100/t = −1.3×10−6 and Δλ111/t = +3.0×10−6 was found.

Saturation magnetization of gallium-substituted yttrium iron garnet

The saturation magnetization of gallium-substituted yttrium iron garnet single crystals of composition Y3[Fe2−x Gax](Fe3−y Gay) O12 with 0≤x+y≤1.5 has been investigated in the temperature range 4.2≤T≤Tc. The magnetization values are below most data of previous investigations on this system. From the fit of the molecular field theory to the experimental results at T=4.2 K the fraction of the tetrahedral gallium ions ft=y/(x+y) could be deduced and are found to range between 1 and 0.91 for 0≤x+y≤1.5. The compensation temperature occurring for x+y&amp;gt;1 has been studied as a function of the gallium distribution.

Über die züchtung von galliumsubstituierten yttrium-eisen-granat-einkristallen aus schmelzflüssiger lösing bei konstanter temperatur

A method is described which allows large gallium substituted yttrium iron garnet single crystals to be grown. This method applies nearly isothermal growth of a seed in a melt with a temperature gradient. Because of good mixing of the melt by accelerated crucible rotation in the presence of a polycrystalline nutrient a very low variation of the gallium content in the crystal is achieved.