Yttrium Iron Garnet Material Research Articles

Conduction in yttrium iron garnets with nickel dopant: Potential for sensor applications

Doped yttrium iron garnet materials exhibit semiconducting behavior and have potential applications in resistive-based sensors, including thermoresistive and gas sensors. In this study, we synthesized Ni-doped yttrium iron garnet samples using the sol-gel method combined with heat treatment. The crystal structure, morphology, and Ni incorporation into the crystal lattice were investigated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy. The saturation magnetization of the samples in the ground state was measured in a Physical Property Measurement System (PPMS) at 5 K. The experimental magnetic moments deviate significantly from the values calculated based on the cation distribution models, suggesting the occupation of Ni2+ and Fe2+ at the octahedral and tetrahedral sites, respectively, with the latter due to oxygen vacancies. We investigated the resistivity, magnetoresistance effect, and hydrogen sensing properties to elucidate the conduction mechanism. At room temperature, the resistivity of the samples decreased sharply as the oxygen vacancy concentration increased, from ∼108 Ωcm in sample x = 0 to ∼106 Ωcm in sample x = 0.08. The resistance of the samples increased when exposed to hydrogen gas, supporting the prediction from the magnetization data that the samples exhibit n-type semiconductor characteristics. The samples showed good sensitivity to H2 gas. At 250°C, sample x = 0.08 exhibits a response of S =11.5, the response time (τres. ∼8 s), and recovery time (τrec. ∼22 s) at 100 ppm hydrogen concentration.

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.

Microstructure and properties of YIG ferrite joint brazed by Fe2O3-doped bismuth composite glass

Bismuth composite glasses doped with Fe 2 O 3 nanoparticles were utilized to braze yttrium iron garnet (YIG) ferrite. The effect of Fe 2 O 3 doping on the thermal property and structure of the composite glasses was studied. The microstructure, mechanical and dielectric properties of YIG/YIG joint were systematically investigated as well. The Fe 2 O 3 doping promoted the crystallization of Bi 2 SiO 5 and the conversion of [BO 4 ] units to [BO 3 ] units. [BO 3 ]/[BO 4 ] in the glass matrix reacted with Y 3+ and Fe 3+ diffusing from YIG base material to form Fe 2 O 3 blocks and lamellar YBO 3 . The gray YBO 3 changed from lamellar phase to needle-like phase with the brazing temperature increasing. The concentration of Fe 3+ increased along with the dissolution of Fe 2 O 3 nanoparticles, resulting in the extensive formation of Fe 2 O 3 nuclei. Consequently, the amount of the Fe 2 O 3 blocks increased with the Fe 2 O 3 doping increasing. The shear strength could reach 68.4 MPa via the combined strengthening of block Fe 2 O 3 and gray YBO 3 phases. The dielectric constant of YIG/YIG joint decreased with the Fe 2 O 3 doping and brazing temperature increasing due to the growth of Fe 2 O 3 and YBO 3 phases. The dielectric loss tangent of the YIG/YIG joint was close to that of the original YIG material with the frequency increasing.

Modeling Reflection-Free One-Way Edge Modes Using Foldy-Lax Multiple Scattering Theory

The Foldy-Lax multiple scattering theory is applied to compute the reflection-free topological one-way edge modes induced by wave interactions with periodic gyromagnetic scatterers. The electromagnetic field response arising from a point source at the interface of two photonic crystals, one comprised of gyromagnetic scatterers, - yttrium-iron-garnet (YIG) scatterers, and the other of alumina scatterers, is studied. The T-matrices of a single cylindrical scatterer of circular cross-section, of both YIG and alumina materials, are derived and utilized to formulate the Foldy-Lax multiple scattering equations. The fields inside and outside the scatterers are derived. Field results of both single-scatterer scattering and multiple-scatterer scattering are compared with results from the method of moments (MoM) and from COMSOL simulations. The comparisons confirm the accuracy of the proposed method and show that the Foldy-Lax multiple-scattering theory is far more efficient than MoM and COMSOL. The proposed approach can be a useful tool for topological wave device analysis and design.

Space-wave isolator based on remanence at microwave frequencies

A platy isolator for plane waves at microwave frequencies is proposed and investigated theoretically. The isolator is a layered structure which consists of a dielectric layer sandwiched by two yttrium-iron-garnet (YIG) layers with opposite remanences. In this isolator structure, there exists a nonreciprocal transverse resonance within the band gap of the YIG materials. The guiding mode related to the transverse resonance exhibits one-way propagation and simultaneously possesses a dispersion band within the light cone in air. Therefore, this nonreciprocal transverse resonance can be excited in the isolator by plane waves incident from air. By using the transfer matrix method, it is shown that high isolation and efficient transmission can be achieved for the proposed isolator without external magnetic field.

Differences in the magnon diffusion length for electrically and thermally driven magnon currents in Y3Fe5O12

Recent demonstration of efficient transport and manipulation of spin information by magnon currents have opened exciting prospects for processing information in devices. Magnon currents can be driven both electrically and thermally, even in magnetic insulators, by applying charge currents in an adjacent metal layer. Earlier reports in thin yttrium iron garnet (YIG) films suggested that the diffusion length of magnons is independent on the biasing method, but different values were obtained in thicker films. Here, we study the magnon diffusion length for electrically and thermally driven magnon currents in the linear regime in a 2-$\mu$m-thick YIG film as a function of temperature and magnetic field. Our results show a decrease of the magnon diffusion length with magnetic field for both biasing methods and at all temperatures from 5 to 300 K, indicating that sub-thermal magnons dominate the long-range transport. Moreover, we demonstrate that the value of the magnon diffusion length depends on the driving mechanism, suggesting that different non-equilibrium magnon distributions are biased for each method. Finally, we demonstrate that the magnon diffusion length for thermally driven magnon currents is independent of the YIG thickness and material growth conditions, confirming that this quantity is an intrinsic parameter of YIG.

From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents.

Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate and excitation of a magnon supercurrent, propelled by a phase gradient in the condensate wave function, can be observed at room temperature by means of the Brillouin light scattering spectroscopy in an yttrium iron garnet material. We study these phenomena in a wide range of external magnetic fields in order to understand their properties when externally pumped magnons are transferred towards the condensed state via two distinct channels: a multistage Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step kinetic instability process. Our main result is that opening the kinetic instability channel leads to the formation of a much denser magnon condensate and to a stronger magnon supercurrent compared to the cascade mechanism alone.

Theory of the spin-Seebeck effect at a topological-insulator/ferromagnetic-insulator interface

The spin-Seebeck effect refers to voltage signals induced in metals by thermally driven spin currents in adjacent magnetic systems. We present a theory of the spin-Seebeck signal in the case where the conductor that supports the voltage signal is the topologically protected two-dimensional surface-state system at the interface between a ferromagnetic insulator (FI) and a topological insulator (TI). Our theory uses a Dirac model for the TI surface-states and assumes Heisenberg exchange coupling between the TI quasiparticles and the FI magnetization. The spin-Seebeck voltage is induced by the TI surface states scattering off the nonequilibrium magnon population at the surface of the semi-infinite thermally driven FI. Our theory is readily generalized to spin-Seebeck voltages in any two-dimensional conductor that is exchange-coupled to the surface of a FI. Surface-state carrier-density-dependent signal strengths calculated using Bi$_2$Te$_3$ and yttrium iron garnet material parameters are consistent with recent experiments.

Structure dependence of magnetic properties in yttrium iron garnet by metal-organic decomposition method**Project supported by the National Natural Science Foundation of China (Grant Nos. 11004095, 11104134, 61271077, 50977042, and 10904061).

The yttrium iron garnet (YIG) samples are prepared at different temperatures from 900 °C to 1300 °C by the metal-organic decomposition (MOD) method. The chemical composition and crystal structure of the samples are studied by scanning electron microscope (SEM), XRD, and Mössbauer spectrometer. It is shown that the ratio of ferric ions on two types of sites, the octahedral and the tetrahedral, is increased with the sintering temperature. At 1300 °C, the pure garnet phase has been obtained, in which the ferric ions ratio is 2:3 leading to the minimum magnetic coercivity and maximum saturation magnetization. These results provide a route to synthesize pure YIG materials as the basic materials used in various spintronics applications.

Dual H- and E-Field Tunable Multiferroic Bandpass Filter at ${\rm K}_{U}$-Band Using Partially Magnetized Spinel Ferrites

A compact dual H- and E-field tunable multiferroic bandpass filters with low magnetic fields using partially magnetized nickel ferrites were designed, fabricated and characterized. Compared to widely used yttrium iron garnet material with a low saturation magnetostriction, nickel ferrite with a much larger saturation magnetostriction was used in this work, which led to higher frequency tunability under electric field. The multiferroic tunable bandpass filters with a NiFe2O4 ferrite/lead magnesium niobate-lead titanate heterostructure at Ku-band, exhibits an H-field tunable of 5.7% under less than 150 Oe bias magnetic field, and an E-field tunable operating frequency range of 270 MHz (2.1%). These dual H- and E-field tunable bandpass filters using partially magnetized spinel ferrites with low magnetic fields lead to Ku-band compact tunable bandpass filters with low power consumption.

Effect of deposition temperature on the properties of sputtered YIG films grown on quartz

Yttrium Iron Garnet (YIG), Y 3Fe 5O 12, is an oxide material that has potential applications in the magneto-optical recording media and microwave device industries. These materials, when synthesized in thin film form, usually require post-deposition annealing in order to enhance their physical properties. Furthermore, integration of YIG based optical components requires the synthesis of high quality YIG material on quartz, a process that may be problematic due to poor adhesion and lattice mismatch. Thus, we have conducted a study on the effect of deposition temperature (from 25 to 800 °C) and post-deposition annealing (at 740 °C) on the crystalline quality and chemical composition of YIG thin films, grown by radio-frequency magnetron sputtering, on quartz substrates. X-ray diffraction (XRD) shows that as-grown layers are amorphous, and subsequent annealing is necessary to induce film crystallization. Rutherford backscattering spectrometry analyses were also conducted and the chemical composition of the films was found to depend on initial deposition temperature and is affected by post-deposition anneals. Comparison of the XRD and RBS results point out to the existence of an optimal deposition temperature at about 700 °C for the formation of high crystalline quality and stoichiometric YIG thin films. Magnetic measurements were found to correlate to the XRD and RBS analyses.

A microstrip tunable negative refractive index metamaterial and phase shifter

A tunable negative refractive index metamaterial and miniature phase shifter have been designed and fabricated in a microstrip configuration for applications in radio frequency integrated circuits. The metamaterial consists of plasmonic copper wires and yttrium iron garnet slabs having a low insertion loss of 5dB at the center of the transmission band. The yttrium iron garnet material enables the magnetic field tuning of the negative refractive index in a dynamic frequency band from 7.0to11.0GHz. The insertion phase can be tuned by 45° continuously by varying the bias field from 3.8to4.6kOe at 9.0GHz.

The magnetic and dielectric properties of microwave sintered yttrium iron garnet (YIG)

Yttrium iron garnet (YIG) material is widely used in microwave devices. Experiments show that microwave sintering (MS) treated YIG materials possess excellent properties with a saturation magnetization of 14.60 emu/g and coercive force 34.82 Oe. In the frequency range of 1 MHz–1.8 GHz, the relative dielectric constant is from 6.5 to 7.0, the line-width is 105 Oe, dielectric loss less than 0.09 and magnetic loss less than 0.7. Furthermore, the sintering time and temperature were significantly reduced from 20 h and 1300 °C for the conventional sintering (CS) process to 2 h and 900 °C for MS technique, respectively.

The low field microwave effective linewidth in polycrystalline ferrites

High precision measurements on the low and high field effective linewidth ΔHeff at 10GHz have been made on ultradense (UD) and conventionally sintered (CS) polycrystalline yttrium iron garnet (YIG) materials. The high field data confirm previous results on the role of two magnon scattering to low wave number (k) electromagnetic Larmor branch spin waves that lie below the light line. The low field data reveal two important contributions to the effective linewidth. For a field regime from the low k edge of the usual dipole exchange spin wave band down to the point in field (H=HX) where above-the-light-line electromagnetic branch Larmor (EML-HI) spin waves appear, ΔHeff is connected with scattering to relatively high k dipole exchange Larmor (DEL) spin waves. The coupling to these modes comes from grain boundaries in the YIG materials. A grain boundary scattering theory gives reasonable agreement with the data. While the high field effective linewidth due to pseudo in-manifold scattering is larger for the CS samples compared to that for the UD samples, the high k DEL scattering is larger for the UD samples compared to that for the CS samples. This is due to the dominant role of the grain boundaries in the low field ΔHeff. For fields below HX, additional scattering appears for the EML-HI modes. The abrupt appearance of an additional ΔHeff component for H&amp;lt;HX provides direct experimental evidence for the presence of such modes in the spin wave dispersion. Part of the loss contribution for H&amp;lt;HX may be due to subthreshold nonlinear effects.

Effect of the pulling rate on the quality of cerium-substituted YIG single-crystal fibers by LHPG

CeO 2 was added into yttrium iron garnet materials (YIG). Samples with a nominal composition of Y 3− x Ce x Fe 5O 12 (Ce:YIG), with x=0–0.4, were grown in air by the laser-heated pedestal growth technique. It is well known that it is difficult to grow pure YIG single-crystal fibers, due to the oscillatory instability of the melt and to the incongruent melting of the compound. In this work CeO 2 was added during the growth of YIG, which caused the composition and the flow in the melt to change. The growth conditions for producing good-quality Ce:YIG single crystal needs to be suitably adjusted in comparison with YIG growth. In the experimental results, it can be seen that the addition of CeO 2 into YIG increases the period of the oscillatory flow in the melt. Moreover, the greater the amount of CeO 2 added, slower is the pulling rate needed to grow good-quality single-crystal fibers. When a faster pulling rate is used to grow Ce:YIG material, more significant amount of foreign phases and cellular structures will form in the core region than in the peripheral region of the grown crystal fibers. This is thought to be due to the fact that the solute concentration and the experimental segregation coefficient along the convex shape of the growth interface in the melt were non-uniform.

Influence of the addition of CeO 2 on the microstructure and the magnetic properties of yttrium iron garnet ceramic

CeO 2 was added into yttrium iron garnet materials (YIG). Samples, with a nominal composition of Y 3− x Ce x Fe 5O 12 (Ce:YIG), with x = 0 - 0.6 , were prepared by a solid-state sintering method. Based on the experimental results, it can be seen that Ce:YIG ceramic with the necessary densification could be fabricated using a lower sintering temperature than that required for pure YIG ceramic. Furthermore, the solubility limit of Ce 3+ ions in this Ce-substituted YIG ceramic, in an ordinary atmosphere, was approximately x = 0.2 . When the Ce 3+ doping content exceeded the solution limit for Ce:YIG ceramic, a foreign CeO 2 phase was residual in the ceramic, which led to impurity of the materials. An excessive addition of CeO 2 ( x = 0.3 , 0.4, 0.6) degrades the remanent magnetization ( B r) and the saturation magnetization, opposite to what occurrs with a small addition of CeO 2 ( x = 0.1 , 0.2). This because the magnetic moment of Ce 3+, when substituted for non-magnetic moment of Y 3+, leads to a slightly enhanced B r and saturation magnetization; non-magnetic inclusion of CeO 2 inside the material however could degrade these characteristics. Nevertheless, the coercivity ( H c) of the Ce-content samples, using the optimized sintering temperature, increased as the addition increased, due to the decrease in grain size. Consequently, a smaller addition of CeO 2 into the YIG material not only lowers the sintering temperature, to achieve a higher density ceramic, but also slightly enhances B r and the saturation magnetization.

Low temperature sintering of microwave magnetic garnet materials

Addition of 2Ca–V or Bi-species into the Yttrium Iron garnet (YIG) materials markedly lowers the sintering temperature necessary for densifying the materials. Sintering temperature ( T s) needed for achieving a density larger than 97% theoretical density decreases form 1450°C×6 h for pure YIG to 1250°C×6 h for 0.6 (2Ca–V)-doped YIG, (Y 1.8Ca 1.2)(Fe 4.4V 0.6)O 12 and to 1020°C×6 h for 1.0 Bi-doped YIG, (Y 2Bi)Fe 5O 12, the Bi species addition not only reduces more markedly the sintering temperature necessary for achieving high density YIG materials, but also degrades loss extensively the magnetic and microwave properties of the materials. As compared with the 2Ca–V incorporation, the magnetic properties of these YIG-series materials vary with the sintering condition pronouncedly even for the samples with the same high density, which is ascribed to the change in granular structure with sintering temperature. Moreover, the linewidth of magnetic resonance peak (△ H) is insignificantly degraded due to Bi- incorporation.